Dot product

Task

Create a function/use an in-built function, to compute the dot product, also known as the scalar product of two vectors.

If possible, make the vectors of arbitrary length.

As an example, compute the dot product of the vectors:

[1, 3, -5] and

[4, -2, -1]

If implementing the dot product of two vectors directly:

each vector must be the same length
multiply corresponding terms from each vector
sum the products (to produce the answer)

Related task

Vector products

8th

Output:

ACL2

<lang Lisp>(defun dotp (v u)

  (if (or (endp v) (endp u))
      0
      (+ (* (first v) (first u))
         (dotp (rest v) (rest u)))))</lang>

> (dotp '(1 3 -5) '(4 -2 -1))
3

<lang ActionScript>function dotProduct(v1:Vector.<Number>, v2:Vector.<Number>):Number { if(v1.length != v2.length) return NaN; var sum:Number = 0; for(var i:uint = 0; i < v1.length; i++) sum += v1[i]*v2[i]; return sum; } trace(dotProduct(Vector.<Number>([1,3,-5]),Vector.<Number>([4,-2,-1])));</lang>

Ada

<lang Ada>with Ada.Text_IO; use Ada.Text_IO; procedure dot_product is type vect is array(Positive range <>) of Integer; v1 : vect := (1,3,-5); v2 : vect := (4,-2,-1);

function dotprod(a: vect; b: vect) return Integer is sum : Integer := 0; begin if not (a'Length=b'Length) then raise Constraint_Error; end if; for p in a'Range loop sum := sum + a(p)*b(p); end loop; return sum; end dotprod;

begin put_line(Integer'Image(dotprod(v1,v2))); end dot_product;</lang>

Output:

Aime

<lang aime>real dp(list a, list b) {

   real p, v;
   integer i;

   p = 0;
   for (i, v in a) {
       p += v * b[i];
   }

p;

}

integer main(void) {

   o_(dp(list(1r, 3r, -5r), list(4r, -2r, -1r)), "\n");

0;

}</lang>

Output:

ALGOL 68

Translation of: C++

Works with: ALGOL 68 version Standard - with prelude inserted manually

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386

<lang algol68>MODE DOTFIELD = REAL; MODE DOTVEC = [1:0]DOTFIELD;

The "Spread Sheet" way of doing a dot product:

 o Assume bounds are equal, and start at 1 
 o Ignore round off error

PRIO SSDOT = 7; OP SSDOT = (DOTVEC a,b)DOTFIELD: (

 DOTFIELD sum := 0;
 FOR i TO UPB a DO sum +:= a[i]*b[i] OD;
 sum

);

An improved dot-product version:

 o Handles sparse vectors
 o Improves summation by gathering round off error
   with no additional multiplication - or LONG - operations.

OP * = (DOTVEC a,b)DOTFIELD: (

 DOTFIELD sum := 0, round off error:= 0;
 FOR i

Assume bounds may not be equal, empty members are zero (sparse) #

   FROM LWB (LWB a > LWB b | a | b )
   TO UPB (UPB a < UPB b | a | b ) 
 DO
   DOTFIELD org = sum, prod = a[i]*b[i];
   sum +:= prod;
   round off error +:= sum - org - prod
 OD;
 sum - round off error

);

Test: #

DOTVEC a=(1,3,-5), b=(4,-2,-1);

print(("a SSDOT b = ",fixed(a SSDOT b,0,real width), new line)); print(("a * b = ",fixed(a * b,0,real width), new line))</lang>

Output:

a SSDOT b = 3.000000000000000
a   *   b = 3.000000000000000

ALGOL W

<lang algolw>begin

   % computes the dot product of two equal length integer vectors            %
   % (single dimension arrays ) the length of the vectors must be specified  %
   % in length.                                                              %
   integer procedure integerDotProduct( integer array a ( * )
                                      ; integer array b ( * )
                                      ; integer value length
                                      ) ;
   begin
       integer product;
       product := 0;
       for i := 1 until length do product := product + ( a(i) * b(i) );
       product
   end integerDotProduct ;

   % declare two vectors of length 3                                         %
   integer array v1, v2 ( 1 :: 3 );
   % initialise the vectors                                                  %
   v1(1) :=  1; v1(2) :=  3; v1(3) := -5;
   v2(1) :=  4; v2(2) := -2; v2(3) := -1;
   % output the dot product                                                  %
   write( integerDotProduct( v1, v2, 3 ) )

end. </lang>

APL

<lang APL>1 3 ¯5 +.× 4 ¯2 ¯1</lang> Output:

AppleScript

Translation of: JavaScript

( functional version )

<lang AppleScript>-- DOT PRODUCT ---------------------------------------------------------------

-- dotProduct :: [Number] -> [Number] -> Number on dotProduct(xs, ys)

   script product
       on |λ|(a, b)
           a * b
       end |λ|
   end script
   
   if length of xs = length of ys then
       sum(zipWith(product, xs, ys))
   else
       missing value -- arrays of differing dimension
   end if

end dotProduct

-- TEST ---------------------------------------------------------------------- on run

   dotProduct([1, 3, -5], [4, -2, -1])
   
   --> 3

end run

-- GENERIC FUNCTIONS ---------------------------------------------------------

-- foldl :: (a -> b -> a) -> a -> [b] -> a on foldl(f, startValue, xs)

   tell mReturn(f)
       set v to startValue
       set lng to length of xs
       repeat with i from 1 to lng
           set v to |λ|(v, item i of xs, i, xs)
       end repeat
       return v
   end tell

end foldl

-- min :: Ord a => a -> a -> a on min(x, y)

   if y < x then
       y
   else
       x
   end if

end min

-- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Script on mReturn(f)

   if class of f is script then
       f
   else
       script
           property |λ| : f
       end script
   end if

end mReturn

-- sum :: [Number] -> Number on sum(xs)

   script add
       on |λ|(a, b)
           a + b
       end |λ|
   end script
   
   foldl(add, 0, xs)

end sum

-- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] on zipWith(f, xs, ys)

   set lng to min(length of xs, length of ys)
   set lst to {}
   tell mReturn(f)
       repeat with i from 1 to lng
           set end of lst to |λ|(item i of xs, item i of ys)
       end repeat
       return lst
   end tell

end zipWith</lang>

Output:

AutoHotkey

<lang AutoHotkey>Vet1 := "1,3,-5" Vet2 := "4 , -2 , -1" MsgBox % DotProduct( Vet1 , Vet2 )

---------------------------

DotProduct( VectorA , VectorB ) {

 Sum := 0
 StringSplit, ArrayA, VectorA, `,, %A_Space%
 StringSplit, ArrayB, VectorB, `,, %A_Space%
 If ( ArrayA0 <> ArrayB0 )
   Return ERROR
 While ( A_Index <= ArrayA0 )
   Sum += ArrayA%A_Index% * ArrayB%A_Index%
 Return Sum

}</lang>

AWK

syntax: GAWK -f DOT_PRODUCT.AWK

BEGIN {

   v1 = "1,3,-5"
   v2 = "4,-2,-1"
   if (split(v1,v1arr,",") != split(v2,v2arr,",")) {
     print("error: vectors are of unequal lengths")
     exit(1)
   }
   printf("%g\n",dot_product(v1arr,v2arr))
   exit(0)

} function dot_product(v1,v2, i,sum) {

   for (i in v1) {
     sum += v1[i] * v2[i]
   }
   return(sum)

} </lang>

Output:

BASIC

Applesoft BASIC

Calculates the dot product of two random vectors of length N. <lang basic>

100 :
110  REM  DOT PRODUCT
120 :
130  REM  INITIALIZE VECTORS OF LENGTH N
140  N = 3
150  DIM V1(N): DIM V2(N)
160  FOR I = 1 TO N
170  V1(I) =  INT ( RND (1) * 20 - 9.5)
180  V2(I) =  INT ( RND (1) * 20 - 9.5)
190  NEXT I
300 :
310  REM  CALCULATE THE DOT PRODUCT
320 :
330  FOR I = 1 TO N:DP = DP + V1(I) * V2(I): NEXT I
400 :
410  REM  DISPLAY RESULT
420 :
430  PRINT "[";: FOR I = 1 TO N: PRINT " ";V1(I);: NEXT I
440  PRINT "] . [";: FOR I = 1 TO N: PRINT " ";V2(I);: NEXT I
450  PRINT "] = ";DP

</lang>

Output:

]RUN
[ 7 2 -2] . [ 7 -5 8] = 23
]RUN
[ -3 -4 -8] . [ -8 7 6] = -52

BBC BASIC

BBC BASIC has a built-in dot-product operator: <lang bbcbasic> DIM vec1(2), vec2(2), dot(0)

     vec1() = 1, 3, -5
     vec2() = 4, -2, -1
     
     dot() = vec1() . vec2()
     PRINT "Result is "; dot(0)</lang>

Output:

Result is 3

bc

<lang bc>/* Calculate the dot product of two vectors a and b (represented as

* arrays) of size n.
*/

define d(a[], b[], n) {

   auto d, i

   for (i = 0; i < n; i++) {
       d += a[i] * b[i]
   }
   return(d)

}

a[0] = 1 a[1] = 3 a[2] = -5 b[0] = 4 b[1] = -2 b[2] = -1 d(a[], b[], 3)</lang>

Output:

Befunge 93

<lang befunge> v Space for variables v Space for vector1 v Space for vector2 v http://rosettacode.org/wiki/Dot_product

                                           >00pv

>>55+":htgneL",,,,,,,,&:0` | v,,,,,,,"Length can't be negative."+55< >,,,,,,,,,,,,,,,,,,,@ |!`-10<

                                     >0.@

v,")".g00,,,,,,,,,,,,,,"Vector a(size " < 0v01g00,")".g00,,,,,,,,,,,,,,"Vector b"< 0pvp2g01&p01-1g01< " g>> 10g0`| @.g30<( 1 >03g:-03p>00g1-` |s 0 vp00-1g00p30+g30*g2-1g00g1-1g00 v # z vp1g01&p01-1g01<> ^ e > 10g0` | vp01-1g01.g1<

>00g1-10p>10g:01-` | " > ^
</lang>

Output:
Length:
3 Vector a(size 3 )1 3 -5 1 3 -5 Vector b(size 3 )4 -2 -1
3
Bracmat
<lang bracmat> ( dot
= a A z Z . !arg:(%?a ?z.%?A ?Z) & !a*!A+dot$(!z.!Z) | 0 )
& out$(dot$(1 3 -5.4 -2 -1));</lang>

Output:
3
C
<lang c>#include <stdio.h>
include <stdlib.h>
int dot_product(int *, int *, size_t);
int main(void) {
int a[3] = {1, 3, -5}; int b[3] = {4, -2, -1};
printf("%d\n", dot_product(a, b, sizeof(a) / sizeof(a[0])));
return EXIT_SUCCESS;
}
int dot_product(int *a, int *b, size_t n) {
int sum = 0; size_t i;
for (i = 0; i < n; i++) { sum += a[i] * b[i]; }
return sum;
}</lang>

Output:
3
C#
<lang csharp>static void Main(string[] args) { Console.WriteLine(DotProduct(new decimal[] { 1, 3, -5 }, new decimal[] { 4, -2, -1 })); Console.Read(); }
private static decimal DotProduct(decimal[] vec1, decimal[] vec2) { if (vec1 == null) return 0;
if (vec2 == null) return 0;
if (vec1.Length != vec2.Length) return 0;
decimal tVal = 0; for (int x = 0; x < vec1.Length; x++) { tVal += vec1[x] * vec2[x]; }
return tVal; }</lang>

Output:
3
Alternative using Linq (C# 4)
Works with: C# version 4
<lang csharp>public static decimal DotProduct(decimal[] a, decimal[] b) {
return a.Zip(b, (x, y) => x * y).Sum();
}</lang>
C++
<lang cpp>#include <iostream>
include <numeric>
int main() {
int a[] = { 1, 3, -5 }; int b[] = { 4, -2, -1 };
std::cout << std::inner_product(a, a + sizeof(a) / sizeof(a[0]), b, 0) << std::endl;
return 0;
}</lang>

Output:
3
Alternative using std::valarray
<lang cpp>
include <valarray>

include <iostream>
int main() {
std::valarray<double> xs = {1,3,-5}; std::valarray<double> ys = {4,-2,-1};
double result = (xs * ys).sum();
std::cout << result << '\n'; return 0;
}</lang>

Output:
3
Clojure
Works with: Clojure version 1.1
Preconditions are new in 1.1. The actual code also works in older Clojure versions. <lang clojure>(defn dot-product [& matrix]
{:pre [(apply == (map count matrix))]} (apply + (apply map * matrix)))
(defn dot-product2 [x y]
(->> (interleave x y) (partition 2 2) (map #(apply * %)) (reduce +)))
(defn dot-product3
"Dot product of vectors. Tested on version 1.8.0." [v1 v2] {:pre [(= (count v1) (count v2))]} (reduce + (map * v1 v2)))
Example Usage
(println (dot-product [1 3 -5] [4 -2 -1])) (println (dot-product2 [1 3 -5] [4 -2 -1])) (println (dot-product3 [1 3 -5] [4 -2 -1])) </lang>
CoffeeScript
<lang coffeescript>dot_product = (ary1, ary2) ->
if ary1.length != ary2.length throw "can't find dot product: arrays have different lengths" dotprod = 0 for v, i in ary1 dotprod += v * ary2[i] dotprod
console.log dot_product([ 1, 3, -5 ], [ 4, -2, -1 ]) # 3 try
console.log dot_product([ 1, 3, -5 ], [ 4, -2, -1, 0 ]) # exception
catch e
console.log e</lang>

Output:
> coffee foo.coffee
3
can't find dot product: arrays have different lengths
Common Lisp
<lang lisp>(defun dot-product (a b)
(apply #'+ (mapcar #'* (coerce a 'list) (coerce b 'list))))</lang>
This works with any size vector, and (as usual for Common Lisp) all numeric types (rationals, bignums, complex numbers, etc.).
Maybe it is better to do it without coercing. Then we got a cleaner code. <lang lisp>(defun dot-prod (a b)
(reduce #'+ (map 'simple-vector #'* a b)))</lang>
Component Pascal
Works with: BlackBox Component Builder
<lang oberon2> MODULE DotProduct; IMPORT StdLog;
PROCEDURE Calculate*(x,y: ARRAY OF INTEGER): INTEGER; VAR i,sum: INTEGER; BEGIN sum := 0; FOR i:= 0 TO LEN(x) - 1 DO INC(sum,x[i] * y[i]); END; RETURN sum END Calculate;
PROCEDURE Test*; VAR i,sum: INTEGER; v1,v2: ARRAY 3 OF INTEGER; BEGIN v1[0] := 1;v1[1] := 3;v1[2] := -5; v2[0] := 4;v2[1] := -2;v2[2] := -1;
StdLog.Int(Calculate(v1,v2));StdLog.Ln END Test;
END DotProduct. </lang> Execute: ^Q DotProduct.Test

Output:
3
D
<lang d>void main() {
import std.stdio, std.numeric;
[1.0, 3.0, -5.0].dotProduct([4.0, -2.0, -1.0]).writeln;
}</lang>

Output:
3
Using an array operation: <lang d>void main() {
import std.stdio, std.algorithm;
double[3] a = [1.0, 3.0, -5.0]; double[3] b = [4.0, -2.0, -1.0]; double[3] c = a[] * b[]; c[].sum.writeln;
}</lang>
Dart
<lang dart>num dot(List<num> A, List<num> B){
if (A.length != B.length){ throw new Exception('Vectors must be of equal size'); } num result = 0; for (int i = 0; i < A.length; i++){ result += A[i] * B[i]; } return result;
}
void main(){
var l = [1,3,-5]; var k = [4,-2,-1]; print(dot(l,k));
}</lang>

Output:
3
Delphi
Works with: Lazarus
<lang delphi>program Project1;
{$APPTYPE CONSOLE}
type
doublearray = array of Double;
function DotProduct(const A, B : doublearray): Double; var I: integer; begin
assert (Length(A) = Length(B), 'Input arrays must be the same length'); Result := 0; for I := 0 to Length(A) - 1 do Result := Result + (A[I] * B[I]);
end;
var
x,y: doublearray;
begin
SetLength(x, 3); SetLength(y, 3); x[0] := 1; x[1] := 3; x[2] := -5; y[0] := 4; y[1] :=-2; y[2] := -1; WriteLn(DotProduct(x,y)); ReadLn;
end.</lang>

Output:
3.00000000000000E+0000
Note: Delphi does not like arrays being declared in procedure headings, so it is necessary to declare it beforehand. To use integers, modify doublearray to be an array of integer.
Déjà Vu
<lang dejavu>dot a b: if /= len a len b: Raise value-error "dot product needs two vectors with the same length"
0 while a: + * pop-from a pop-from b
!. dot [ 1 3 -5 ] [ 4 -2 -1 ]</lang>

Output:
3
DWScript
For arbitrary length vectors, using a precondition to check vector length: <lang delphi>function DotProduct(a, b : array of Float) : Float; require
a.Length = b.Length;
var
i : Integer;
begin
Result := 0; for i := 0 to a.High do Result += a[i]*b[i];
end;
PrintLn(DotProduct([1,3,-5], [4,-2,-1]));</lang> Using built-in 4D Vector type: <lang delphi>var a := Vector(1, 3, -5, 0); var b := Vector(4, -2, -1, 0);
PrintLn(a * b);</lang>

Ouput in both cases:

3
EchoLisp
<lang lisp> (define a #(1 3 -5)) (define b #(4 -2 -1))
function definition
(define ( ⊗ a b) (for/sum ((x a)(y b)) (* x y))) (⊗ a b) → 3
library
(lib 'math) (dot-product a b) → 3 </lang>
Eiffel
<lang Eiffel>class APPLICATION
create make
feature {NONE} -- Initialization
make -- Run application. do print(dot_product(<<1, 3, -5>>, <<4, -2, -1>>).out) end
feature -- Access
dot_product (a, b: ARRAY[INTEGER]): INTEGER -- Dot product of vectors `a' and `b'. require a.lower = b.lower a.upper = b.upper local i: INTEGER do from i := a.lower until i > a.upper loop Result := Result + a[i] * b[i] i := i + 1 end end end</lang>

Ouput:

3
Ela
Translation of: Haskell
<lang ela>open list
dotp a b | length a == length b = sum (zipWith (*) a b)
| else = fail "Vector sizes must match."
dotp [1,3,-5] [4,-2,-1]</lang>

Output:
3
Elena
ELENA 4.x : <lang elena>import extensions; import system'routines;
extension op {
method dotProduct(int[] array) = self.zipBy(array, (x,y => x * y)).summarize();
}
public program() {
console.printLine(new int[]{1, 3, -5}.dotProduct(new int[]{4, -2, -1}))
}</lang>

Output:
3
Elixir
Translation of: Erlang
<lang elixir>defmodule Vector do
def dot_product(a,b) when length(a)==length(b), do: dot_product(a,b,0) def dot_product(_,_) do raise ArgumentError, message: "Vectors must have the same length." end defp dot_product([],[],product), do: product defp dot_product([h1|t1], [h2|t2], product), do: dot_product(t1, t2, product+h1*h2)
end
IO.puts Vector.dot_product([1,3,-5],[4,-2,-1])</lang>

Output:
3
Emacs Lisp
<lang Emacs Lisp> (defun dot-product (v1 v2)
(setq res 0) (dotimes (i (length v1)) (setq res (+ (* (elt v1 i) (elt v2 i) ) res) )) res)
(progn
(insert (format "%d\n" (dot-product [1 2 3] [1 2 3]) )) (insert (format "%d\n" (dot-product '(1 2 3) '(1 2 3) ))))
</lang> Output:
14 14
Erlang
<lang erlang>dotProduct(A,B) when length(A) == length(B) -> dotProduct(A,B,0); dotProduct(_,_) -> erlang:error('Vectors must have the same length.').
dotProduct([H1|T1],[H2|T2],P) -> dotProduct(T1,T2,P+H1*H2); dotProduct([],[],P) -> P.
dotProduct([1,3,-5],[4,-2,-1]).</lang>

Output:
3
Euphoria
<lang Euphoria>function dotprod(sequence a, sequence b)
atom sum a *= b sum = 0 for n = 1 to length(a) do sum += a[n] end for return sum
end function
? dotprod({1,3,-5},{4,-2,-1})</lang>

Output:
3
<lang Euphoria>-- Here is an alternative method, -- using the standard Euphoria Version 4+ Math Library include std/math.e sequence a = {1,3,-5}, b = {4,-2,-1} -- Make them any length you want ? sum(a * b)</lang>

Output:
3
F#
<lang fsharp>let dot_product (a:array<'a>) (b:array<'a>) =
if Array.length a <> Array.length b then failwith "invalid argument: vectors must have the same lengths" Array.fold2 (fun acc i j -> acc + (i * j)) 0 a b</lang>
> dot_product [| 1; 3; -5 |] [| 4; -2; -1 |] ;; val it : int = 3
Factor
The built-in word v. is used to compute the dot product. It doesn't enforce that the vectors are of the same length, so here's a wrapper. <lang factor>USING: kernel math.vectors sequences ;
dot-product ( u v -- w )
2dup [ length ] bi@ = [ v. ] [ "Vector lengths must be equal" throw ] if ;</lang>
( scratchpad ) { 1 3 -5 } { 4 -2 -1 } dot-product . 3
FALSE
<lang false>[[\1-$0=~][$d;2*1+\-ø\$d;2+\-ø@*@+]#]p: 3d: {Vectors' length} 1 3 5_ 4 2_ 1_ d;$1+ø@*p;!%. {Output: 3}</lang>
Fantom
Dot product of lists of Int: <lang fantom>class DotProduct {
static Int dotProduct (Int[] a, Int[] b) { Int result := 0 [a.size,b.size].min.times |i| { result += a[i] * b[i] } return result }
public static Void main () { Int[] x := [1,2,3,4] Int[] y := [2,3,4]
echo ("Dot product of $x and $y is ${dotProduct(x, y)}") }
}</lang>
Fōrmulæ
In this page you can see the solution of this task.
Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text (more info). Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for transportation effects more than visualization and edition.
The option to show Fōrmulæ programs and their results is showing images. Unfortunately images cannot be uploaded in Rosetta Code.
Forth
<lang forth>: vector create cells allot ;
th cells + ;
3 constant /vector /vector vector a /vector vector b
dotproduct ( a1 a2 -- n)
0 tuck ?do -rot over i th @ over i th @ * >r rot r> + loop nip nip

vector! cells over + swap ?do i ! 1 cells +loop ;
-5 3 1 a /vector vector! -1 -2 4 b /vector vector!
a b /vector dotproduct . 3 ok</lang>
Fortran
<lang fortran>program test_dot_product
write (*, '(i0)') dot_product ([1, 3, -5], [4, -2, -1])
end program test_dot_product</lang>

Output:
3
The intrinsic function Dot_Product(X,Y) accepts various precisions of integer, floating-point and complex arrays (for which it is Sum(Conjg(x)*y)) and even logical, for which it is Any(x .AND. y) returning zero if either array is of length zero, or false for logical types.
FunL
<lang funl>import lists.zipWith
def dot( a, b )
| a.length() == b.length() = sum( zipWith((*), a, b) ) | otherwise = error( "Vector sizes must match" )
println( dot([1, 3, -5], [4, -2, -1]) )</lang>

Output:
3
GAP
<lang gap># Built-in
[1, 3, -5]*[4, -2, -1];
3</lang>
Go
Implementation
<lang go>package main
import (
"errors" "fmt" "log"
)
var (
v1 = []int{1, 3, -5} v2 = []int{4, -2, -1}
)
func dot(x, y []int) (r int, err error) {
if len(x) != len(y) { return 0, errors.New("incompatible lengths") } for i, xi := range x { r += xi * y[i] } return
}
func main() {
d, err := dot([]int{1, 3, -5}, []int{4, -2, -1}) if err != nil { log.Fatal(err) } fmt.Println(d)
}</lang>

Output:
3
Library gonum/floats
<lang go>package main
import (
"fmt"
"github.com/gonum/floats"
)
var (
v1 = []float64{1, 3, -5} v2 = []float64{4, -2, -1}
)
func main() {
fmt.Println(floats.Dot(v1, v2))
}</lang>

Output:
3
Groovy
Solution: <lang groovy>def dotProduct = { x, y ->
assert x && y && x.size() == y.size() [x, y].transpose().collect{ xx, yy -> xx * yy }.sum()
}</lang> Test: <lang groovy>println dotProduct([1, 3, -5], [4, -2, -1])</lang>

Output:
3
Haskell
<lang haskell>dotp :: Num a => [a] -> [a] -> a dotp a b | length a == length b = sum (zipWith (*) a b)
| otherwise = error "Vector sizes must match"
main = print $ dotp [1, 3, -5] [4, -2, -1] -- prints 3</lang>
Or, using the Maybe monad to avoid exceptions and keep things composable: <lang haskell>dotp
:: Num a => [a] -> [a] -> Maybe a
dotp a b
| length a == length b = Just $ sum (zipWith (*) a b) | otherwise = Nothing
main :: IO () main = mbPrint $ dotp [1, 3, -5] [4, -2, -1] -- prints 3
mbPrint
:: Show a => Maybe a -> IO ()
mbPrint (Just x) = print x mbPrint n = print n</lang>
Hy
<lang clojure>(defn dotp [a b]
(assert (= (len a) (len b))) (sum (genexpr (* aterm bterm) [(, aterm bterm) (zip a b)])))
(assert (= 3 (dotp [1 3 -5] [4 -2 -1])))</lang>
Icon and Unicon
The procedure below computes the dot product of two vectors of arbitrary length or generates a run time error if its arguments are the wrong type or shape. <lang Icon>procedure main() write("a dot b := ",dotproduct([1, 3, -5],[4, -2, -1])) end
procedure dotproduct(a,b) #: return dot product of vectors a & b or error if *a ~= *b & type(a) == type(b) == "list" then runerr(205,a) # invalid value every (dp := 0) +:= a[i := 1 to *a] * b[i] return dp end</lang>
IDL
<lang IDL> a = [1, 3, -5] b = [4, -2, -1] c = a#TRANSPOSE(b) c = TOTAL(a*b,/PRESERVE_TYPE) </lang>
Idris
<lang idris>module Main
import Data.Vect
dotProduct : (Num a) => Vect n a -> Vect n a -> a dotProduct = (sum .) . zipWith (*)
main : IO () main = printLn $ dotProduct [1,2,3] [1,2,3] </lang>
J
<lang j> 1 3 _5 +/ . * 4 _2 _1 3
dotp=: +/ . * NB. Or defined as a verb (function) 1 3 _5 dotp 4 _2 _1
3</lang> Note also: The verbs built using the conjunction . generally apply to matricies and arrays of higher dimensions and can be built with verbs (functions) other than sum ( +/ ) and product ( * ).
Spelling issue: The conjunction . needs to be preceded by a space. This is because J's spelling rules say that if the character '.' is preceded by any other character, it is included in the same parser token that included that other character. In other words, 1.23e4, '...' and /. are each examples of "parser tokens".
Java
<lang java>public class DotProduct {
public static void main(String[] args) { double[] a = {1, 3, -5}; double[] b = {4, -2, -1};
System.out.println(dotProd(a,b)); }
public static double dotProd(double[] a, double[] b){ if(a.length != b.length){ throw new IllegalArgumentException("The dimensions have to be equal!"); } double sum = 0; for(int i = 0; i < a.length; i++){ sum += a[i] * b[i]; } return sum; } }</lang>

Output:
3.0
JavaScript
ES5
<lang javascript>function dot_product(ary1, ary2) {
if (ary1.length != ary2.length) throw "can't find dot product: arrays have different lengths"; var dotprod = 0; for (var i = 0; i < ary1.length; i++) dotprod += ary1[i] * ary2[i]; return dotprod;
}
print(dot_product([1,3,-5],[4,-2,-1])); // ==> 3 print(dot_product([1,3,-5],[4,-2,-1,0])); // ==> exception</lang>
We could also use map and reduce in lieu of iteration,
<lang javascript>function dotp(x,y) {
function dotp_sum(a,b) { return a + b; } function dotp_times(a,i) { return x[i] * y[i]; } if (x.length != y.length) throw "can't find dot product: arrays have different lengths"; return x.map(dotp_times).reduce(dotp_sum,0);
}
dotp([1,3,-5],[4,-2,-1]); // ==> 3 dotp([1,3,-5],[4,-2,-1,0]); // ==> exception</lang>
ES6
Composing functional primitives into a dotProduct() which returns undefined (rather than an error) when the array lengths are unmatched.
<lang JavaScript>(() => {
'use strict';
// dotProduct :: [Int] -> [Int] -> Int const dotProduct = (xs, ys) => { const sum = xs => xs ? xs.reduce((a, b) => a + b, 0) : undefined;
return xs.length === ys.length ? ( sum(zipWith((a, b) => a * b, xs, ys)) ) : undefined; }
// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] const zipWith = (f, xs, ys) => { const ny = ys.length; return (xs.length <= ny ? xs : xs.slice(0, ny)) .map((x, i) => f(x, ys[i])); }
return dotProduct([1, 3, -5], [4, -2, -1]);
})();</lang>

Output:
<lang JavaScript>3</lang>
jq
The dot-product of two arrays, x and y, can be computed using dot(x;y) defined as follows: <lang jq> def dot(x; y):
reduce range(0;x|length) as $i (0; . + x[$i] * y[$i]);
</lang>
Suppose however that we are given an array of objects, each of which has an "x" field and a "y" field, and that we wish to compute SIGMA( x * y ) where the sum is taken over the array, and where x and y denote the values in the "x" and "y" fields respectively.
This can most usefully be accomplished in jq with the aid of SIGMA(f) defined as follows:<lang jq>def SIGMA( f ): reduce .[] as $o (0; . + ($o | f )) ;</lang> Given the array of objects as input, the dot-product is then simply SIGMA( .x * .y ).
Example:<lang jq>dot( [1, 3, -5]; [4, -2, -1]) # => 3
[ {"x": 1, "y": 4}, {"x": 3, "y": -2}, {"x": -5, "y": -1} ]
| SIGMA( .x * .y ) # => 3</lang>
Julia
Dot products and many other linear-algebra functions are built-in functions in Julia (and are largely implemented by calling functions from LAPACK). <lang julia>x = [1, 3, -5] y = [4, -2, -1] z = dot(x, y) z = x'*y</lang>
K
<lang K> +/1 3 -5 * 4 -2 -1 3
1 3 -5 _dot 4 -2 -1
3</lang>
Kotlin
Works with: Kotlin version 1.0+
<lang scala>fun dot(v1: Array<Double>, v2: Array<Double>) =
v1.zip(v2).map { it.first * it.second }.reduce { a, b -> a + b }
fun main(args: Array<String>) {
dot(arrayOf(1.0, 3.0, -5.0), arrayOf(4.0, -2.0, -1.0)).let { println(it) }
}</lang>

Output:
3.0
LFE
<lang lisp>(defun dot-product (a b)
(: lists foldl #'+/2 0 (: lists zipwith #'*/2 a b)))
</lang>
Liberty BASIC
<lang lb>vectorA$ = "1, 3, -5" vectorB$ = "4, -2, -1" print "DotProduct of ";vectorA$;" and "; vectorB$;" is "; print DotProduct(vectorA$, vectorB$)
'arbitrary length vectorA$ = "3, 14, 15, 9, 26" vectorB$ = "2, 71, 18, 28, 1" print "DotProduct of ";vectorA$;" and "; vectorB$;" is "; print DotProduct(vectorA$, vectorB$)
end
function DotProduct(a$, b$)
DotProduct = 0 i = 1 while 1 x$=word$( a$, i, ",") y$=word$( b$, i, ",") if x$="" or y$="" then exit function DotProduct = DotProduct + val(x$)*val(y$) i = i+1 wend
end function </lang>
Logo
<lang logo>to dotprod :a :b
output apply "sum (map "product :a :b)
end
show dotprod [1 3 -5] [4 -2 -1] ; 3</lang>
Logtalk
<lang logtalk>dot_product(A, B, Sum) :-
dot_product(A, B, 0, Sum).
dot_product([], [], Sum, Sum). dot_product([A| As], [B| Bs], Acc, Sum) :-
Acc2 is Acc + A*B, dot_product(As, Bs, Acc2, Sum).</lang>
Lua
<lang lua>function dotprod(a, b)
local ret = 0 for i = 1, #a do ret = ret + a[i] * b[i] end return ret
end
print(dotprod({1, 3, -5}, {4, -2, 1}))</lang>
M2000 Interpreter
<lang M2000 Interpreter> Module dot_product {
A=(1,3,-5) B=(4,-2,-1) Function Dot(a, b) { if len(a)<>len(b) Then Error "not same length" if len(a)=0 then Error "empty vectors" Let a1=each(a), b1=each(b), sum=0 While a1, b1 {sum+=array(a1)*array(b1)} =sum } Print Dot(A, B) Print Dot((1,3,-5), (4,-2,-1))
} Module dot_product </lang>

Maple
Between Arrays, Vectors, or Matrices you can use the dot operator: <lang Maple><1,2,3> . <4,5,6></lang> <lang Maple>Array([1,2,3]) . Array([4,5,6])</lang>
Between any of the above or lists, you can use the LinearAlgebra[DotProduct] function: <lang Maple>LinearAlgebra( <1,2,3>, <4,5,6> )</lang> <lang Maple>LinearAlgebra( Array([1,2,3]), Array([4,5,6]) )</lang> <lang Maple>LinearAlgebra([1,2,3], [4,5,6] )</lang>
Mathematica / Wolfram Language
<lang Mathematica>{1,3,-5}.{4,-2,-1}</lang>
MATLAB
The dot product operation is a built-in function that operates on vectors of arbitrary length. <lang matlab>A = [1 3 -5] B = [4 -2 -1] C = dot(A,B)</lang> For the Octave implimentation: <lang matlab>function C = DotPro(A,B)
C = sum( A.*B );
end</lang>
Maxima
<lang maxima>[1, 3, -5] . [4, -2, -1]; /* 3 */</lang>
Mercury
This will cause a software_error/1 exception if the lists are of different lengths. <lang mercury>:- module dot_product.
- interface.
- import_module io.

- pred main(io::di, io::uo) is det.
- implementation.

- import_module int, list.
main(!IO) :-
io.write_int([1, 3, -5] `dot_product` [4, -2, -1], !IO), io.nl(!IO).
- func dot_product(list(int), list(int)) = int.
dot_product(As, Bs) =
list.foldl_corresponding((func(A, B, Acc) = Acc + A * B), As, Bs, 0).</lang>
МК-61/52
<lang>С/П * ИП0 + П0 С/П БП 00</lang>
Input: В/О x₁ С/П x₂ С/П y₁ С/П y₂ С/П ...
Modula-2
<lang modula2>MODULE DotProduct; FROM RealStr IMPORT RealToStr; FROM Terminal IMPORT WriteString,WriteLn,ReadChar;
TYPE Vector =
RECORD x,y,z : REAL END;
PROCEDURE DotProduct(u,v : Vector) : REAL; BEGIN
RETURN u.x*v.x + u.y*v.y + u.z*v.z
END DotProduct;
VAR
buf : ARRAY[0..63] OF CHAR; dp : REAL;
BEGIN
dp := DotProduct(Vector{1.0,3.0,-5.0},Vector{4.0,-2.0,-1.0}); RealToStr(dp, buf); WriteString(buf); WriteLn;
ReadChar
END DotProduct.</lang>
MUMPS
<lang MUMPS>DOTPROD(A,B)
;Returns the dot product of two vectors. Vectors are assumed to be stored as caret-delimited strings of numbers. ;If the vectors are not of equal length, a null string is returned. QUIT:$LENGTH(A,"^")'=$LENGTH(B,"^") "" NEW I,SUM SET SUM=0 FOR I=1:1:$LENGTH(A,"^") SET SUM=SUM+($PIECE(A,"^",I)*$PIECE(B,"^",I)) KILL I QUIT SUM</lang>
Nemerle
This will cause an exception if the arrays are different lengths. <lang Nemerle>using System; using System.Console; using Nemerle.Collections.NCollectionsExtensions;
module DotProduct {
DotProduct(x : array[int], y : array[int]) : int { $[(a * b)|(a, b) in ZipLazy(x, y)].FoldLeft(0, _+_); } Main() : void { def arr1 = array[1, 3, -5]; def arr2 = array[4, -2, -1]; WriteLine(DotProduct(arr1, arr2)); }
}</lang>
NetRexx
<lang NetRexx>/* NetRexx */ options replace format comments java crossref savelog symbols binary
whatsTheVectorVictor = [[double 1.0, 3.0, -5.0], [double 4.0, -2.0, -1.0]] dotProduct = Rexx dotProduct(whatsTheVectorVictor) say dotProduct.format(null, 2)
return
method dotProduct(vec1 = double[], vec2 = double[]) public constant returns double signals IllegalArgumentException
if vec1.length \= vec2.length then signal IllegalArgumentException('Vectors must be the same length')
scalarProduct = double 0.0 loop e_ = 0 to vec1.length - 1 scalarProduct = vec1[e_] * vec2[e_] + scalarProduct end e_
return scalarProduct
method dotProduct(vecs = double[,]) public constant returns double signals IllegalArgumentException
return dotProduct(vecs[0], vecs[1])</lang>
newLISP
<lang newLISP>(define (dot-product x y)
(apply + (map * x y)))
(println (dot-product '(1 3 -5) '(4 -2 -1)))</lang>
Nim
<lang nim># Compile time error when a and b are differently sized arrays
Runtime error when a and b are differently sized seqs
proc dotp[T](a,b: T): int =
assert a.len == b.len for i in a.low..a.high: result += a[i] * b[i]
echo dotp([1,3,-5], [4,-2,-1]) echo dotp(@[1,2,3],@[4,5,6])</lang>
Oberon-2
Works with: oo2c version 2
<lang oberon2> MODULE DotProduct; IMPORT
Out := NPCT:Console;
VAR
x,y: ARRAY 3 OF LONGINT;
PROCEDURE DotProduct(a,b: ARRAY OF LONGINT): LONGINT; VAR
resp, i: LONGINT;
BEGIN
ASSERT(LEN(a) = LEN(b)); resp := 0; FOR i := 0 TO LEN(x) - 1 DO INC(resp,x[i]*y[i]) END; RETURN resp
END DotProduct;
BEGIN
x[0] := 1;y[0] := 4; x[1] := 3;y[1] := -2; x[2] := -5;y[2] := -1; Out.Int(DotProduct(x,y),0);Out.Ln
END DotProduct. </lang>

Output:
3
Objective-C
<lang objc>#import <stdio.h>
import <stdint.h>

import <stdlib.h>

import <string.h>

import <Foundation/Foundation.h>
// this class exists to return a result between two // vectors: if vectors have different "size", valid // must be NO @interface VResult : NSObject {
@private double value; BOOL valid;
} +(instancetype)new: (double)v isValid: (BOOL)y; -(instancetype)init: (double)v isValid: (BOOL)y; -(BOOL)isValid; -(double)value; @end
@implementation VResult +(instancetype)new: (double)v isValid: (BOOL)y {
return [[self alloc] init: v isValid: y];
} -(instancetype)init: (double)v isValid: (BOOL)y {
if ((self == [super init])) { value = v; valid = y; } return self;
} -(BOOL)isValid { return valid; } -(double)value { return value; } @end

@interface RCVector : NSObject {
@private double *vec; uint32_t size;
} +(instancetype)newWithArray: (double *)v ofLength: (uint32_t)l; -(instancetype)initWithArray: (double *)v ofLength: (uint32_t)l; -(VResult *)dotProductWith: (RCVector *)v; -(uint32_t)size; -(double *)array; -(void)free; @end
@implementation RCVector +(instancetype)newWithArray: (double *)v ofLength: (uint32_t)l {
return [[self alloc] initWithArray: v ofLength: l];
} -(instancetype)initWithArray: (double *)v ofLength: (uint32_t)l {
if ((self = [super init])) { size = l; vec = malloc(sizeof(double) * l); if ( vec == NULL ) return nil; memcpy(vec, v, sizeof(double)*l); } return self;
} -(void)dealloc {
free(vec);
} -(uint32_t)size { return size; } -(double *)array { return vec; } -(VResult *)dotProductWith: (RCVector *)v {
double r = 0.0; uint32_t i, s; double *v1; if ( [self size] != [v size] ) return [VResult new: r isValid: NO]; s = [self size]; v1 = [v array]; for(i = 0; i < s; i++) { r += vec[i] * v1[i]; } return [VResult new: r isValid: YES];
} @end
double val1[] = { 1, 3, -5 }; double val2[] = { 4,-2, -1 };
int main() {
@autoreleasepool { RCVector *v1 = [RCVector newWithArray: val1 ofLength: sizeof(val1)/sizeof(double)]; RCVector *v2 = [RCVector newWithArray: val2 ofLength: sizeof(val1)/sizeof(double)]; VResult *r = [v1 dotProductWith: v2]; if ( [r isValid] ) { printf("%lf\n", [r value]); } else { fprintf(stderr, "length of vectors differ\n"); } } return 0;
}</lang>
Objeck
<lang objeck>bundle Default {
class DotProduct { function : Main(args : String[]) ~ Nil { DotProduct([1, 3, -5], [4, -2, -1])->PrintLine(); } function : DotProduct(array_a : Int[], array_b : Int[]) ~ Int { if(array_a = Nil) { return 0; }; if(array_b = Nil) { return 0; }; if(array_a->Size() <> array_b->Size()) { return 0; }; val := 0; for(x := 0; x < array_a->Size(); x += 1;) { val += (array_a[x] * array_b[x]); }; return val; } }
}</lang>
OCaml
With lists: <lang ocaml>let dot = List.fold_left2 (fun z x y -> z +. x *. y) 0.
(*
dot [1.0; 3.0; -5.0] [4.0; -2.0; -1.0];;
- : float = 3.
)</lang>
With arrays: <lang ocaml>let dot v u =
if Array.length v <> Array.length u then invalid_arg "Different array lengths"; let times v u = Array.mapi (fun i v_i -> v_i *. u.(i)) v in Array.fold_left (+.) 0. (times v u)
(*
dot [| 1.0; 3.0; -5.0 |] [| 4.0; -2.0; -1.0 |];;
- : float = 3.
)</lang>
Octave
See Dot product#MATLAB for an implementation. If we have a row-vector and a column-vector, we can use simply *. <lang octave>a = [1, 3, -5] b = [4, -2, -1] % or [4; -2; -1] and avoid transposition with ' disp( a * b' ) % ' means transpose</lang>
Oforth
<lang Oforth>: dotProduct zipWith(#*) sum ;</lang>

Output:
>[ 1, 3, -5] [ 4, -2, -1 ] dotProduct . 3
Ol
<lang scheme> (define (dot-product a b)
(apply + (map * a b)))
(print (dot-product '(1 3 -5) '(4 -2 -1)))
==> 3
</lang>
Oz
Vectors are represented as lists in this example. <lang oz>declare
fun {DotProduct Xs Ys} {Length Xs} = {Length Ys} %% assert {List.foldL {List.zip Xs Ys Number.'*'} Number.'+' 0} end
in
{Show {DotProduct [1 3 ~5] [4 ~2 ~1]}}</lang>
PARI/GP
<lang parigp>dot(u,v)={
sum(i=1,#u,u[i]*v[i])
};</lang>
Pascal
See Delphi
Perl
<lang perl>sub dotprod {
my($vec_a, $vec_b) = @_; die "they must have the same size\n" unless @$vec_a == @$vec_b; my $sum = 0; $sum += $vec_a->[$_] * $vec_b->[$_] for 0..$#$vec_a; return $sum;
}
my @vec_a = (1,3,-5); my @vec_b = (4,-2,-1);
print dotprod(\@vec_a,\@vec_b), "\n"; # 3</lang>
Perl 6
Works with: Rakudo version 2010.07
We use the square-bracket meta-operator to turn the infix operator + into a reducing list operator, and the guillemet meta-operator to vectorize the infix operator *. Length validation is automatic in this form. <lang perl6>say [+] (1, 3, -5) »*« (4, -2, -1);</lang>
Phix
<lang Phix>?sum(sq_mul({1,3,-5},{4,-2,-1}))</lang>

Output:
3
PHP
<lang php><?php function dot_product($v1, $v2) {
if (count($v1) != count($v2)) throw new Exception('Arrays have different lengths'); return array_sum(array_map('bcmul', $v1, $v2));
}
echo dot_product(array(1, 3, -5), array(4, -2, -1)), "\n"; ?></lang>
PicoLisp
<lang PicoLisp>(de dotProduct (A B)
(sum * A B) )
(dotProduct (1 3 -5) (4 -2 -1))</lang>

Output:
-> 3
PL/I
<lang PL/I>get (n); begin;
declare (A(n), B(n)) float; declare dot_product float;
get list (A); get list (B); dot_product = sum(a*b); put (dot_product);
end;</lang>
PostScript
<lang postscript>/dotproduct{ /x exch def /y exch def /sum 0 def /i 0 def x length y length eq %Check if both arrays have the same length { x length{ /sum x i get y i get mul sum add def /i i 1 add def }repeat sum == } { -1 == }ifelse }def</lang>
PowerShell
<lang PowerShell> function dotproduct( $a, $b) {
$a | foreach -Begin {$i = $res = 0} -Process { $res += $_*$b[$i++] } -End{$res}
} dotproduct (1..2) (1..2) dotproduct (1..10) (11..20) </lang> Output:
5 935
Prolog
Works with SWI-Prolog. <lang Prolog>dot_product(L1, L2, N) :- maplist(mult, L1, L2, P), sumlist(P, N).
mult(A,B,C) :- C is A*B.</lang> Example :
?- dot_product([1,3,-5], [4,-2,-1], N). N = 3.
PureBasic
<lang PureBasic>Procedure dotProduct(Array a(1),Array b(1))
Protected i, sum, length = ArraySize(a())
If ArraySize(a()) = ArraySize(b()) For i = 0 To length sum + a(i) * b(i) Next EndIf
ProcedureReturn sum
EndProcedure
If OpenConsole()
Dim a(2) Dim b(2) a(0) = 1 : a(1) = 3 : a(2) = -5 b(0) = 4 : b(1) = -2 : b(2) = -1 PrintN(Str(dotProduct(a(),b()))) Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input() CloseConsole()
EndIf</lang>
Python
<lang python>def dotp(a,b):
assert len(a) == len(b), 'Vector sizes must match' return sum(aterm * bterm for aterm,bterm in zip(a, b))
if __name__ == '__main__':
a, b = [1, 3, -5], [4, -2, -1] assert dotp(a,b) == 3</lang>
R
Here are several ways to do the task. <lang R>x <- c(1, 3, -5) y <- c(4, -2, -1)
sum(x*y) # compute products, then do the sum x %*% y # inner product
loop implementation
dotp <- function(x, y) { n <- length(x) if(length(y) != n) stop("invalid argument") s <- 0 for(i in 1:n) s <- s + x[i]*y[i] s }
dotp(x, y)</lang>
Racket
<lang Racket>
lang racket
(define (dot-product l r) (for/sum ([x l] [y r]) (* x y)))
(dot-product '(1 3 -5) '(4 -2 -1))
dot-product works on sequences such as vectors

(dot-product #(1 2 3) #(4 5 6)) </lang>
Rascal
<lang Rascal>import List;
public int dotProduct(list[int] L, list[int] M){ result = 0; if(size(L) == size(M)) { while(size(L) >= 1) { result += (head(L) * head(M)); L = tail(L); M = tail(M); } return result; } else { throw "vector sizes must match"; } }</lang>
Alternative solution
If a matrix is represented by a relation of <x-coordinate, y-coordinate, value>, then function below can be used to find the Dot product. <lang Rascal>import Prelude;
public real matrixDotproduct(rel[real x, real y, real v] column1, rel[real x, real y, real v] column2){ return (0.0 | it + v1*v2 | <x1,y1,v1> <- column1, <x2,y2,v2> <- column2, y1==y2); }
//a matrix, given by a relation of x-coordinate, y-coordinate, value. public rel[real x, real y, real v] matrixA = { <0.0,0.0,12.0>, <0.0,1.0, 6.0>, <0.0,2.0,-4.0>, <1.0,0.0,-51.0>, <1.0,1.0,167.0>, <1.0,2.0,24.0>, <2.0,0.0,4.0>, <2.0,1.0,-68.0>, <2.0,2.0,-41.0> };</lang>
REBOL
<lang REBOL>REBOL []
a: [1 3 -5] b: [4 -2 -1]
dot-product: function [v1 v2] [sum] [
if (length? v1) != (length? v2) [ make error! "error: vector sizes must match" ] sum: 0 repeat i length? v1 [ sum: sum + ((pick v1 i) * (pick v2 i)) ]
]
dot-product a b</lang>
REXX
no error checking
<lang rexx>/*REXX program computes the dot product of two equal size vectors (of any size).*/
vectorA = ' 1 3 -5 ' /*populate vector A with some numbers*/ vectorB = ' 4 -2 -1 ' /* " " B " " " */
say 'vector A = ' vectorA /*display the elements in the vector A.*/ say 'vector B = ' vectorB /* " " " " " " B.*/ p=.Prod(vectorA, vectorB) /*invoke function & compute dot product*/ say /*display a blank line for readability.*/ say 'dot product = ' p /*display the dot product to terminal. */ exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ .Prod: procedure; parse arg A,B /*this function compute the dot product*/
$=0 /*initialize the sum to 0 (zero). */ do j=1 for words(A) /*multiply each number in the vectors. */ $=$+word(A,j) * word(B,j) /* ··· and add the product to the sum.*/ end /*j*/ return $ /*return the sum to function's invoker.*/</lang>
output using the default (internal) inputs:
vector A = 1 3 -5 vector B = 4 -2 -1 dot product = 3
with error checking
<lang rexx>/*REXX program computes the dot product of two equal size vectors (of any size).*/
vectorA = ' 1 3 -5 ' /*populate vector A with some numbers*/ vectorB = ' 4 -2 -1 ' /* " " B " " " */
say 'vector A = ' vectorA /*display the elements in the vector A.*/ say 'vector B = ' vectorB /* " " " " " " B.*/ p=.prod(vectorA, vectorB) /*invoke function & compute dot product*/ say /*display a blank line for readability.*/ say 'dot product = ' p /*display the dot product to terminal. */ exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ .prod: procedure; parse arg A,B /*this function compute the dot product*/
lenA = words(A); @.1= 'A' /*the number of numbers in vector A. */ lenB = words(B); @.2= 'B' /* " " " " " " B. */ /*Also, define 2 literals to hold names*/ if lenA\==lenB then do; say "***error*** vectors aren't the same size:" /*oops*/ say ' vector A length = ' lenA say ' vector B length = ' lenB exit 13 /*exit pgm with bad─boy return code 13.*/ end $=0 /*initialize the sum to 0 (zero). */ do j=1 for lenA /*multiply each number in the vectors. */ #.1=word(A,j) /*use array to hold 2 numbers at a time*/ #.2=word(B,j) do k=1 for 2; if datatype(#.k,'N') then iterate say "***error*** vector " @.k ' element' j, " isn't numeric: " n.k; exit 13 end /*k*/ $=$ + #.1 * #.2 /* ··· and add the product to the sum.*/ end /*j*/ return $ /*return the sum to function's invoker.*/</lang>
output is the same as the 1^st REXX version.

Ring
<lang ring> aVector = [2, 3, 5] bVector = [4, 2, 1] sum = 0 see dotProduct(aVector, bVector)
func dotProduct cVector, dVector
for n = 1 to len(aVector) sum = sum + cVector[n] * dVector[n] next return sum
</lang>
RLaB
In its simplest form dot product is a composition of two functions: element-by-element multiplication '.*' followed by sumation of an array. Consider an example: <lang RLaB>x = rand(1,10); y = rand(1,10); s = sum( x .* y );</lang> Warning: element-by-element multiplication is matrix optimized. As the interpretation of the matrix optimization is quite general, and unique to RLaB, any two matrices can be so multiplied irrespective of their dimensions. It is up to user to check whether in his/her case the matrix optimization needs to be restricted, and then to implement restrictions in his/her code.
Ruby
With the standard library, require 'matrix' and call Vector#inner_product. <lang ruby>irb(main):001:0> require 'matrix' => true irb(main):002:0> Vector[1, 3, -5].inner_product Vector[4, -2, -1] => 3</lang> Or implement dot product. <lang ruby>class Array
def dot_product(other) raise "not the same size!" if self.length != other.length self.zip(other).inject(0) {|dp, (a, b)| dp += a*b} end
end
p [1, 3, -5].dot_product [4, -2, -1] # => 3</lang>

Run BASIC
<lang runbasic>v1$ = "1, 3, -5" v2$ = "4, -2, -1"
print "DotProduct of ";v1$;" and "; v2$;" is ";dotProduct(v1$,v2$) end
function dotProduct(a$, b$)
while word$(a$,i + 1,",") <> "" i = i + 1 v1$=word$(a$,i,",") v2$=word$(b$,i,",") dotProduct = dotProduct + val(v1$) * val(v2$) wend
end function</lang>
Rust
Implemented as a simple function with check for equal length of vectors. <lang rust>// alternatively, fn dot_product(a: &Vec<u32>, b: &Vec<u32>) // but using slices is more general and rustic fn dot_product(a: &[i32], b: &[i32]) -> Option<i32> {
if a.len() != b.len() { return None } Some( a.iter() .zip( b.iter() ) .fold(0, |sum, (el_a, el_b)| sum + el_a*el_b) )
}

fn main() {
let v1 = vec![1, 3, -5]; let v2 = vec![4, -2, -1];
println!("{}", dot_product(&v1, &v2).unwrap());
}</lang>

Alternatively as a very generic function which works for any two types that can be multiplied to result in a third type which can be added with itself. Works with any argument convertible to an Iterator of known length (ExactSizeIterator).
Uses an unstable feature. <lang rust>#![feature(zero_one)] // <-- unstable feature use std::ops::{Add, Mul}; use std::num::Zero;
fn dot_product<T1, T2, U, I1, I2>(lhs: I1, rhs: I2) -> Option
where T1: Mul<T2, Output = U>, U: Add<U, Output = U> + Zero, I1: IntoIterator<Item = T1>, I2: IntoIterator<Item = T2>, I1::IntoIter: ExactSizeIterator, I2::IntoIter: ExactSizeIterator,
{
let (iter_lhs, iter_rhs) = (lhs.into_iter(), rhs.into_iter()); match (iter_lhs.len(), iter_rhs.len()) { (0, _) | (_, 0) => None, (a,b) if a != b => None, (_,_) => Some( iter_lhs.zip(iter_rhs) .fold(U::zero(), |sum, (a, b)| sum + (a * b)) ) }
}

fn main() {
let v1 = vec![1, 3, -5]; let v2 = vec![4, -2, -1];
println!("{}", dot_product(&v1, &v2).unwrap());
}</lang>

S-lang
<lang S-lang>print(sum([1, 3, -5] * [4, -2, -1]));</lang>

Output:
3.0
[sum() returns a double from integer arrays]
Sather
Built-in class VEC "implements" euclidean (geometric) vectors. <lang sather>class MAIN is
main is x ::= #VEC(|1.0, 3.0, -5.0|); y ::= #VEC(|4.0, -2.0, -1.0|); #OUT + x.dot(y) + "\n"; end;
end;</lang>
Scala
Library: Scala

<lang scala>class Dot[T](v1: Seq[T])(implicit n: Numeric[T]) {

import n._ // import * operator def dot(v2: Seq[T]) = { require(v1.size == v2.size) (v1 zip v2).map{ Function.tupled(_ * _)}.sum }
}
object Main extends App {
implicit def toDot[T: Numeric](v1: Seq[T]) = new Dot(v1)
val v1 = List(1, 3, -5) val v2 = List(4, -2, -1) println(v1 dot v2)
}</lang>
Seed7
<lang seed7>$ include "seed7_05.s7i";
$ syntax expr: .().dot.() is -> 6; # priority of dot operator
const func integer: (in array integer: a) dot (in array integer: b) is func
result var integer: sum is 0; local var integer: index is 0; begin if length(a) <> length(b) then raise RANGE_ERROR; else for index range 1 to length(a) do sum +:= a[index] * b[index]; end for; end if; end func;
const proc: main is func
begin writeln([](1, 3, -5) dot [](4, -2, -1)); end func;</lang>
Sidef
<lang ruby>func dot_product(a, b) {
(a »*« b)«+»;
}; say dot_product([1,3,-5], [4,-2,-1]); # => 3</lang>
Scheme
Works with: Scheme version R $^{5}$ RS
<lang scheme>(define (dot-product a b)
(apply + (map * a b)))
(display (dot-product '(1 3 -5) '(4 -2 -1))) (newline)</lang>

Output:
3
Scilab
<lang Scilab>A = [1 3 -5] B = [4 -2 -1] C = sum(A.*B)</lang>
Slate
<lang slate>v@(Vector traits) <dot> w@(Vector traits) "Dot-product." [
(0 below: (v size min: w size)) inject: 0 into: [| :sum :index | sum + ((v at: index) * (w at: index))]
].</lang>
Smalltalk
Works with: GNU Smalltalk
<lang smalltalk>Array extend [
* anotherArray [ |acc| acc := 0. self with: anotherArray collect: [ :a :b | acc := acc + ( a * b ) ]. ^acc ]
]
( #(1 3 -5) * #(4 -2 -1 ) ) printNl.</lang>
SNOBOL4
<lang snobol4> define("dotp(a,b)sum,i") :(dotp_end) dotp i = 1; sum = 0 loop sum = sum + (a * b)
i = i + 1 ?a :s(loop) dotp = sum :(return)
dotp_end
a = array(3); a<1> = 1; a<2> = 3; a<3> = -5; b = array(3); b<1> = 4; b<2> = -2; b<3> = -1; output = dotp(a,b)
end</lang>
SPARK
Works with SPARK GPL 2010 and GPS GPL 2010.
By defining numeric subtypes with suitable ranges we can prove statically that there will be no run-time errors. (The Simplifier leaves 2 VCs unproven, but these are clearly provable by inspection.)
The precondition enforces equality of the ranges of the two vectors. <lang ada>with Spark_IO; --# inherit Spark_IO; --# main_program; procedure Dot_Product_Main --# global in out Spark_IO.Outputs; --# derives Spark_IO.Outputs from *; is
Limit : constant := 1000; type V_Elem is range -Limit .. Limit; V_Size : constant := 100; type V_Index is range 1 .. V_Size; type Vector is array(V_Index range <>) of V_Elem;
type V_Prod is range -(Limit**2)*V_Size .. (Limit**2)*V_Size; --# assert V_Prod'Base is Integer;
subtype Index3 is V_Index range 1 .. 3; subtype Vector3 is Vector(Index3); Vect1 : constant Vector3 := Vector3'(1, 3, -5); Vect2 : constant Vector3 := Vector3'(4, -2, -1);
function Dot_Product(V1, V2 : Vector) return V_Prod --# pre V1'First = V2'First --# and V1'Last = V2'Last; is Sum : V_Prod := 0; begin for I in V_Index range V1'Range --# assert Sum in -(Limit**2)*V_Prod(I-1) .. (Limit**2)*V_Prod(I-1); loop Sum := Sum + V_Prod(V1(I)) * V_Prod(V2(I)); end loop; return Sum; end Dot_Product;
begin
Spark_IO.Put_Integer(File => Spark_IO.Standard_Output, Item => Integer(Dot_Product(Vect1, Vect2)), Width => 6, Base => 10);
end Dot_Product_Main;</lang>

Output:
3
SQL
ANSI sql does not support functions and is missing some other concepts that would be needed for a general case implementation of inner product (column names and tables would need to be first class in SQL -- capable of being passed to functions).
However, inner product is fairly simple to specify in SQL.
Given two tables A and B where A has key columns i and j and B has key columns j and k and both have value columns N, the inner product of A and B would be: <lang sql>select i, k, sum(A.N*B.N) as N
from A inner join B on A.j=B.j group by i, k</lang>
Standard ML
With lists: <lang sml>val dot = ListPair.foldlEq Real.*+ 0.0
(* - dot ([1.0, 3.0, ~5.0], [4.0, ~2.0, ~1.0]); val it = 3.0 : real
)</lang>
With vectors: <lang sml>fun dot (v, u) = (
if Vector.length v <> Vector.length u then raise ListPair.UnequalLengths else (); Vector.foldli (fn (i, v_i, z) => v_i * Vector.sub (u, i) + z) 0.0 v )
(* - dot (#[1.0, 3.0, ~5.0], #[4.0, ~2.0, ~1.0]); val it = 3.0 : real
)</lang>
Stata
With row vectors:
<lang stata>matrix a=1,3,-5 matrix b=4,-2,-1 matrix c=a*b' di el("c",1,1)</lang>
With column vectors:
<lang stata>matrix a=1\3\-5 matrix b=4\-2\-1 matrix c=a'*b di el("c",1,1)</lang>
Mata
With row vectors:
<lang stata>a=1,3,-5 b=4,-2,-1 a*b'</lang>
With column vectors:
<lang stata>a=1\3\-5 b=4\-2\-1 a'*b</lang>
In both cases, one cas also write
<lang stata>sum(a:*b)</lang>
Swift
Works with: Swift version 1.2+
<lang swift>func dot(v1: [Double], v2: [Double]) -> Double {
return reduce(lazy(zip(v1, v2)).map(*), 0, +)
}
println(dot([1, 3, -5], [4, -2, -1]))</lang>

Output:
3.0
Tcl
Library: Tcllib (Package: math::linearalgebra)
<lang tcl>package require math::linearalgebra
set a {1 3 -5} set b {4 -2 -1} set dotp [::math::linearalgebra::dotproduct $a $b] proc pp vec {return \[[join $vec ,]\]} puts "[pp $a] \u2219 [pp $b] = $dotp"</lang>

Output:
[1,3,-5] ∙ [4,-2,-1] = 3.0
TI-83 BASIC
To perform a matrix dot product on TI-83, the trick is to use lists (and not to use matrices). <lang ti83b>sum({1,3,–5}*{4,–2,–1})</lang>

Output:
3
TI-89 BASIC
dotP([1, 3, –5], [4, –2, –1])

Output:
3
Ursala
A standard library function for dot products of floating point numbers exists, but a new one can be defined for integers as shown using the map operator (*) with the zip suffix (p) to construct a "zipwith" operator (*p), which operates on the integer product function. A catchable exception is thrown if the list lengths are unequal. This function is then composed (+) with a cumulative summation function, which is constructed from the binary sum function, and the reduction operator (:-) with 0 specified for the vacuous sum. <lang Ursala>#import int
dot = sum:-0+ product*p
cast %z
test = dot(<1,3,-5>,<4,-2,-1>)</lang>

Output:
3
VBScript
<lang vb> WScript.Echo DotProduct("1,3,-5","4,-2,-1")
Function DotProduct(vector1,vector2) arrv1 = Split(vector1,",") arrv2 = Split(vector2,",") If UBound(arrv1) <> UBound(arrv2) Then WScript.Echo "The vectors are not of the same length." Exit Function End If DotProduct = 0 For i = 0 To UBound(arrv1) DotProduct = DotProduct + (arrv1(i) * arrv2(i)) Next End Function </lang>

Output:
3
Visual Basic .NET
Translation of: C#
<lang vbnet>Module Module1
Function DotProduct(a As Decimal(), b As Decimal()) As Decimal Return a.Zip(b, Function(x, y) x * y).Sum() End Function
Sub Main() Console.WriteLine(DotProduct({1, 3, -5}, {4, -2, -1})) Console.ReadLine() End Sub
End Module</lang>

Output:
3
Wart
<lang python>def (dot_product x y)
(sum+map (*) x y)</lang>
+ is punned (overloaded) here; when applied to functions it denotes composition. Also, (*) is used to skip infix expansion.

Output:
(dot_product '(1 3 -5) '(4 -2 -1)) => 3
X86 Assembly
Using FASM. Targets x64 Microsoft Windows. <lang asm>format PE64 console entry start
include 'win64a.inc'
section '.text' code readable executable
start: stdcall dotProduct, vA, vB invoke printf, msg_num, rax stdcall dotProduct, vA, vC invoke printf, msg_num, rax invoke ExitProcess, 0 proc dotProduct vectorA, vectorB mov rax, [rcx] cmp rax, [rdx] je .calculate invoke printf, msg_sizeMismatch mov rax, 0 ret .calculate: mov r8, rcx add r8, 8 mov r9, rdx add r9, 8 mov rcx, rax mov rax, 0 mov rdx, 0 .next: mov rbx, [r9] imul rbx, [r8] add rax, rbx add r8, 8 add r9, 8 loop .next ret endp
section '.data' data readable
msg_num db "%d", 0x0D, 0x0A, 0 msg_sizeMismatch db "Size mismatch; can't calculate.", 0x0D, 0x0A, 0 struc Vector [symbols] { common .length dq (.end - .symbols) / 8 .symbols dq symbols .end: } vA Vector 1, 3, -5 vB Vector 4, -2, -1 vC Vector 7, 2, 9, 0
section '.idata' import data readable writeable
library kernel32, 'KERNEL32.DLL',\ msvcrt, 'MSVCRT.DLL'
include 'api/kernel32.inc'
import msvcrt,\ printf, 'printf'</lang>

Output:

<lang>3

Size mismatch; can't calculate. 0</lang>
XPL0
<lang XPL0>include c:\cxpl\codes;
func DotProd(U, V, L); int U, V, L; int S, I; [S:= 0; for I:= 0 to L-1 do S:= S + U(I)*V(I); return S; ];
[IntOut(0, DotProd([1, 3, -5], [4, -2, -1], 3)); CrLf(0); ]</lang>

Output:
3
Yabasic
<lang Yabasic> sub sq_mul(a(), b(), c()) local n, i
n = arraysize(a(), 1)
for i = 1 to n c(i) = a(i) * b(i) next i end sub
sub sq_sum(a()) local n, i, r
n = arraysize(a(), 1)
for i = 1 to n r = r + a(i) next i return r end sub
dim a(3), b(3), c(3)
a(1) = 1 : a(2) = 3 : a(3) = -5 b(1) = 4 : b(2) = -2 : b(3) = -1 sq_mul(a(), b(), c())
print sq_sum(c()) </lang>
zkl
<lang zkl>fcn dotp(a,b){Utils.zipWith('*,a,b).sum()}</lang> zipWith stops at the shortest of the lists

Output:
dotp(T(1,3,-5),T(4,-2,-1,666)) //-->3
If exact length is a requirement <lang zkl>fcn dotp2(a,b){if(a.len()!=b.len())throw(Exception.ValueError);
Utils.zipWith('*,a,b).sum()
}</lang>
ZX Spectrum Basic
<lang zxbasic>10 DIM a(3): LET a(1)=1: LET a(2)=3: LET a(3)=-5 20 DIM b(3): LET b(1)=4: LET b(2)=-2: LET b(3)=-1 30 LET sum=0 40 FOR i=1 TO 3: LET sum=sum+a(i)*b(i): NEXT i 50 PRINT sum</lang>