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Task.

Discovered by Leonhard Euler around 1730, it is the most ubiquitous mathematical constant after pi and e, but appears more arcane than these.

Denoted gamma (γ), it measures the amount by which the partial sums of the harmonic series (the simplest diverging series) differ from the logarithmic function (its approximating integral): lim _{n → ∞} (1 + 1/2 + 1/3 + … + 1/n − log(n)).

The definition of γ converges too slowly to be numerically useful, but in 1735 Euler himself applied his recently discovered summation formula to compute ‘the notable number’ accurate to 15 places. For a single-precision implementation this is still the most economic algorithm.

In 1961, the young Donald Knuth used Euler's method to evaluate γ to 1271 places. Knuth found that the computation of the Bernoulli numbers required in the Euler-Maclaurin formula was the most time-consuming part of the procedure.

The next year Dura Sweeney computed 3566 places, using a formula based on the expansion of the exponential integral which didn't need Bernoulli numbers. It's a bit-hungry method though: 2d digits of working precision obtain d correct places only.

This was remedied in 1988 by David Bailey; meanwhile Richard Brent and Ed McMillan had published an even more efficient algorithm based on Bessel function identities and found 30100 places in 20 hours time.

Nowadays the old records have far been exceeded: over 6·10¹¹ decimal places are already known. These massive computations suggest that γ is neither rational nor algebraic, but this is yet to be proven.

References.

[1] Gourdon and Sebah, The Euler constant γ. (for all formulas)

[2] Euler's original journal article translated from the latin (p. 9)

Burlesque

Subject to double rounding error, evaluates 33 partial terms in a series

33ro{JroJJJL[\/JL[\/nr\/{-1}\/.*FLJL[ro?^?*\/JL[{2}\/.*FL\/?^?*\/{1.+}m[J{lg}m[\/?/?*++\/1 3.0./\/?^.*}m[++-2 3 2lg.*./.*2lg2./.+

Output:

0.5772156649015326

C

Single precision

/*********************************************
Subject: Comparing five methods for
         computing Euler's constant 0.5772...
tested : tcc-0.9.27
--------------------------------------------*/
#include <math.h>
#include <stdio.h>

#define eps 1e-6

int main(void) {
double a, b, h, n2, r, u, v;
int k, k2, m, n;

printf("From the definition, err. 3e-10\n");

n = 400;

h = 1;
for (k = 2; k <= n; k++) {
   h += 1.0 / k;
}
//faster convergence: Negoi, 1997
a = log(n +.5 + 1.0 / (24*n));

printf("Hn    %.16f\n", h);
printf("gamma %.16f\nk = %d\n\n", h - a, n);


printf("Sweeney, 1963, err. idem\n");

n = 21;

double s[] = {0, n};
r = n;
k = 1;
do {
   k += 1;
   r *= (double) n / k;
   s[k & 1] += r / k;
} while (r > eps);

printf("gamma %.16f\nk = %d\n\n", s[1] - s[0] - log(n), k);


printf("Bailey, 1988\n");

n = 5;

a = 1;
h = 1;
n2 = pow(2,n);
r = 1;
k = 1;
do {
   k += 1;
   r *= n2 / k;
   h += 1.0 / k;
   b = a; a += r * h;
} while (fabs(b - a) > eps);
a *= n2 / exp(n2);

printf("gamma %.16f\nk = %d\n\n", a - n * log(2), k);


printf("Brent-McMillan, 1980\n");

n = 13;

a = -log(n);
b = 1;
u = a;
v = b;
n2 = n * n;
k2 = 0;
k = 0;
do {
   k2 += 2*k + 1;
   k += 1;
   a *= n2 / k;
   b *= n2 / k2;
   a = (a + b) / k;
   u += a;
   v += b;
} while (fabs(a) > eps);

printf("gamma %.16f\nk = %d\n\n", u / v, k);


printf("How Euler did it in 1735\n");
//Bernoulli numbers with even indices
double B2[] = {1.0,1.0/6,-1.0/30,1.0/42,-1.0/30,\
 5.0/66,-691.0/2730,7.0/6,-3617.0/510,43867.0/798};
m = 7;
if (m > 9) return(0);

n = 10;

//n-th harmonic number
h = 1;
for (k = 2; k <= n; k++) {
   h += 1.0 / k;
}
printf("Hn    %.16f\n", h);

h -= log(n);
printf("  -ln %.16f\n", h);

//expansion C = -digamma(1)
a = -1.0 / (2*n);
n2 = n * n;
r = 1;
for (k = 1; k <= m; k++) {
   r *= n2;
   a += B2[k] / (2*k * r);
}

printf("err  %.16f\ngamma %.16f\nk = %d", a, h + a, n + m);

printf("\n\nC  =  0.57721566490153286...\n");
}

output:

From the definition, err. 3e-10
Hn    6.5699296911765055
gamma 0.5772156645765731
k = 400

Sweeney, 1963, err. idem
gamma 0.5772156645636311
k = 68

Bailey, 1988
gamma 0.5772156649015341
k = 89

Brent-McMillan, 1980
gamma 0.5772156649015329
k = 40

How Euler did it in 1735
Hn    2.9289682539682538
  -ln 0.6263831609742079
err  -0.0491674960726754
gamma 0.5772156649015325
k = 17

C  =  0.57721566490153286...

Multi precision

From first principles

/**************************************************
Subject: Computation of Euler's constant 0.5772...
         with the Brent-McMillan algorithm B1,
         Math. Comp. 34 (1980), 305-312
tested : tcc-0.9.27 with gmp 6.2.0
-------------------------------------------------*/
#include <gmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

//multi-precision float pointers
mpf_ptr u, v, k2;

//precision parameters
unsigned long e10, e2;
long e;
double f;

//log(x/y) with the Taylor series for atanh(x-y/x+y)
void ln (mpf_ptr s, unsigned long x, unsigned long y) {
mpf_ptr d = u, q = v;
unsigned long k;
   //Möbius transformation
   k = x; x -= y; y += k;

   if (x != 1) {
      printf ("ln: illegal argument x - y != 1");
      exit;
   }

   //s = 1 / (x + y)
   mpf_set_ui (s, y);
   mpf_ui_div (s, 1, s);
   //k2 = s * s
   mpf_mul (k2, s, s);
   mpf_set (d, s);

   k = 1;
   do {
      k += 2;
      //d *= k2
      mpf_mul (d, d, k2);
      //q = d / k
      mpf_div_ui (q, d, k);
      //s += q
      mpf_add (s, s, q);

      f = mpf_get_d_2exp (&e, q);
   } while (abs(e) < e2);

   //s *= 2
   mpf_mul_2exp (s, s, 1);
}

int main (void) {
mpf_ptr a = malloc(sizeof(__mpf_struct));
mpf_ptr b = malloc(sizeof(__mpf_struct));
u = malloc(sizeof(__mpf_struct));
v = malloc(sizeof(__mpf_struct));
k2 = malloc(sizeof(__mpf_struct));
//unsigned long integers
unsigned long k, n, n2, r, s, t;

clock_t tim = clock();

// n = 2^i * 3^j * 5^k

// log(n) = r * log(16/15) + s * log(25/24) + t * log(81/80)

// solve linear system for r, s, t
//  4 -3 -4| i
// -1 -1  4| j
// -1  2 -1| k

//examples
t = 1;
switch (t) {
case 1 :
   n = 60;
   r = 41;
   s = 30;
   t = 18;
//100 digits
break;
case 2 :
   n = 4800;
   r = 85;
   s = 62;
   t = 37;
//8000 digits, 0.6 s
break;
case 3 :
   n = 9375;
   r = 91;
   s = 68;
   t = 40;
//15625 digits, 2.5 s
break;
default :
   n = 18750;
   r = 98;
   s = 73;
   t = 43;
//31250 digits, 12 s. @2.00GHz
}

//decimal precision
e10 = n / .6;
//binary precision
e2 = (1 + e10) / .30103;

//initialize mpf's
mpf_set_default_prec (e2);
mpf_inits (a, b, u, v, k2, (mpf_ptr)0);

//Compute log terms

ln (b, 16, 15);

//a = r * b
mpf_mul_ui (a, b, r);

ln (b, 25, 24);

//a += s * b
mpf_mul_ui (u, b, s);
mpf_add (a, a, u);

ln (b, 81, 80);

//a += t * b
mpf_mul_ui (u, b, t);
mpf_add (a, a, u);

//gmp_printf ("log(%lu) %.*Ff\n", n, e10, a);

//B&M, algorithm B1

//a = -a, b = 1
mpf_neg (a, a);
mpf_set_ui (b, 1);
mpf_set (u, a);
mpf_set (v, b);

k = 0;
n2 = n * n;
//k2 = k * k
mpf_set_ui (k2, 0);
do {
   //k2 += 2k + 1
   mpf_add_ui (k2, k2, (k << 1) + 1);
   k += 1;

   //b = b * n2 / k2
   mpf_div (b, b, k2);
   mpf_mul_ui (b, b, n2);
   //a = (a * n2 / k + b) / k
   mpf_div_ui (a, a, k);
   mpf_mul_ui (a, a, n2);
   mpf_add (a, a, b);
   mpf_div_ui (a, a, k);

   //u += a, v += b
   mpf_add (u, u, a);
   mpf_add (v, v, b);

   f = mpf_get_d_2exp (&e, a);
} while (abs(e) < e2);

mpf_div (u, u, v);
gmp_printf ("gamma %.*Ff (maxerr. 1e-%lu)\n", e10, u, e10);

gmp_printf ("k = %lu\n\n", k);

tim = clock() - tim;
printf("time: %.7f s\n",((double)tim)/CLOCKS_PER_SEC);
}

output:

gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-100)
k = 255

The easy way

/*******************************************
Subject: Euler's constant 0.5772...
tested : tcc-0.9.27 with mpfr 4.1.0
------------------------------------------*/
#include <gmp.h>
#include <mpfr.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main (void) {
mpfr_ptr a = malloc(sizeof(__mpfr_struct));
unsigned long e2, e10;
clock_t tim = clock();

//decimal precision
e10 = 100;

//binary precision
e2 = (1 + e10) / .30103;
mpfr_init2 (a, e2);

mpfr_const_euler (a, MPFR_RNDN);
mpfr_printf ("gamma %.*Rf\n\n", e10, a);

tim = clock() - tim;
gmp_printf ("time: %.7f s\n",((double)tim)/CLOCKS_PER_SEC);
}

FreeBASIC

Single precision

'**********************************************
'Subject: Comparing five methods for
'         computing Euler's constant 0.5772...
'tested : FreeBasic 1.08.1
'----------------------------------------------
const eps = 1e-6
dim as double a, b, h, n2, r, u, v
dim as integer k, k2, m, n

? "From the definition, err. 3e-10"

n = 400

h = 1
for k = 2 to n
   h += 1 / k
next k
'faster convergence: Negoi, 1997
a = log(n +.5 + 1 / (24*n))

? "Hn   "; h
? "gamma"; h - a; !"\nk ="; n
?


? "Sweeney, 1963, err. idem"

n = 21

dim as double s(1) = {0, n}
r = n
k = 1
do
   k += 1
   r *= n / k
   s(k and 1) += r / k
loop until r < eps

? "gamma"; s(1) - s(0) - log(n); !"\nk ="; k
?


? "Bailey, 1988"

n = 5

a = 1
h = 1
n2 = 2^n
r = 1
k = 1
do
   k += 1
   r *= n2 / k
   h += 1 / k
   b = a: a += r * h
loop until abs(b - a) < eps
a *= n2 / exp(n2)

? "gamma"; a - n * log(2); !"\nk ="; k
?


? "Brent-McMillan, 1980"

n = 13

a = -log(n)
b = 1
u = a
v = b
n2 = n * n
k2 = 0
k = 0
do
   k2 += 2*k + 1
   k += 1
   a *= n2 / k
   b *= n2 / k2
   a = (a + b) / k
   u += a
   v += b
loop until abs(a) < eps

? "gamma"; u / v; !"\nk ="; k
?


? "How Euler did it in 1735"
'Bernoulli numbers with even indices
dim as double B2(9) = {1,1/6,-1/30,1/42,_
 -1/30,5/66,-691/2730,7/6,-3617/510,43867/798}
m = 7
if m > 9 then end

n = 10

'n-th harmonic number
h = 1
for k = 2 to n
   h += 1 / k
next k
? "Hn   "; h

h -= log(n)
? "  -ln"; h

'expansion C = -digamma(1)
a = -1 / (2*n)
n2 = n * n
r = 1
for k = 1 to m
   r *= n2
   a += B2(k) / (2*k * r)
next k

? "err  "; a; !"\ngamma"; h + a; !"\nk ="; n + m
?
? "C  =  0.57721566490153286..."
end

output:

From the definition, err. 3e-10
Hn    6.569929691176506
gamma 0.5772156645765731
k = 400

Sweeney, 1963, err. idem
gamma 0.5772156645636311
k = 68

Bailey, 1988
gamma 0.5772156649015341
k = 89

Brent-McMillan, 1980
gamma 0.5772156649015329
k = 40

How Euler did it in 1735
Hn    2.928968253968254
  -ln 0.6263831609742079
err  -0.04916749607267539
gamma 0.5772156649015325
k = 17

C  =  0.57721566490153286...

Multi precision

From first principles

'***************************************************
'Subject: Computation of Euler's constant 0.5772...
'         with the Brent-McMillan algorithm B1,
'         Math. Comp. 34 (1980), 305-312
'tested : FreeBasic 1.08.1 with gmp 6.2.0
'---------------------------------------------------
#include "gmp.bi"

'multi-precision float pointers
Dim as mpf_ptr a, b
Dim shared as mpf_ptr k2, u, v
'unsigned long integers
Dim as ulong k, n, n2, r, s, t
'precision parameters
Dim shared as ulong e10, e2
Dim shared e as clong
Dim shared f as double
Dim as double tim = TIMER
CLS

a = allocate(len(__mpf_struct))
b = allocate(len(__mpf_struct))
u = allocate(len(__mpf_struct))
v = allocate(len(__mpf_struct))
k2 = allocate(len(__mpf_struct))

'log(x/y) with the Taylor series for atanh(x-y/x+y)
Sub ln (byval s as mpf_ptr, byval x as ulong, byval y as ulong)
Dim as mpf_ptr d = u, q = v
Dim k as ulong
   'Möbius transformation
   k = x: x -= y: y += k

   If x <> 1 Then
      Print "ln: illegal argument x - y <> 1"
      End
   End If

   's = 1 / (x + y)
   mpf_set_ui (s, y)
   mpf_ui_div (s, 1, s)
   'k2 = s * s
   mpf_mul (k2, s, s)
   mpf_set (d, s)

   k = 1
   Do
      k += 2
      'd *= k2
      mpf_mul (d, d, k2)
      'q = d / k
      mpf_div_ui (q, d, k)
      's += q
      mpf_add (s, s, q)

      f = mpf_get_d_2exp (@e, q)
   Loop until abs(e) > e2

   's *= 2
   mpf_mul_2exp (s, s, 1)
End Sub

'Main

'n = 2^i * 3^j * 5^k

'log(n) = r * log(16/15) + s * log(25/24) + t * log(81/80)

'solve linear system for r, s, t
' 4 -3 -4| i
'-1 -1  4| j
'-1  2 -1| k

'examples
t = 1
select case t
case 1
   n = 60
   r = 41
   s = 30
   t = 18
'100 digits
case 2
   n = 4800
   r = 85
   s = 62
   t = 37
'8000 digits, 0.6 s
case 3
   n = 9375
   r = 91
   s = 68
   t = 40
'15625 digits, 2.5 s
case else
   n = 18750
   r = 98
   s = 73
   t = 43
'31250 digits, 12 s. @2.00GHz
end select

'decimal precision
e10 = n / .6
'binary precision
e2 = (1 + e10) / .30103

'initialize mpf's
mpf_set_default_prec (e2)
mpf_inits (a, b, u, v, k2, Cptr(mpf_ptr, 0))

'Compute log terms

ln b, 16, 15

'a = r * b
mpf_mul_ui (a, b, r)

ln b, 25, 24

'a += s * b
mpf_mul_ui (u, b, s)
mpf_add (a, a, u)

ln b, 81, 80

'a += t * b
mpf_mul_ui (u, b, t)
mpf_add (a, a, u)

''gmp_printf (!"log(%lu) %.*Ff\n", n, e10, a)

'B&M, algorithm B1

'a = -a, b = 1
mpf_neg (a, a)
mpf_set_ui (b, 1)
mpf_set (u, a)
mpf_set (v, b)

k = 0
n2 = n * n
'k2 = k * k
mpf_set_ui (k2, 0)
do
   'k2 += 2k + 1
   mpf_add_ui (k2, k2, (k shl 1) + 1)
   k += 1

   'b = b * n2 / k2
   mpf_div (b, b, k2)
   mpf_mul_ui (b, b, n2)
   'a = (a * n2 / k + b) / k
   mpf_div_ui (a, a, k)
   mpf_mul_ui (a, a, n2)
   mpf_add (a, a, b)
   mpf_div_ui (a, a, k)

   'u += a, v += b
   mpf_add (u, u, a)
   mpf_add (v, v, b)

   f = mpf_get_d_2exp (@e, a)
Loop until abs(e) > e2

mpf_div (u, u, v)
gmp_printf (!"gamma %.*Ff (maxerr. 1e-%lu)\n", e10, u, e10)

gmp_printf (!"k = %lu\n\n", k)

gmp_printf (!"time: %.7f s\n", TIMER - tim)
end

output:

gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-100)
k = 255

The easy way

' ******************************************
'Subject: Euler's constant 0.5772...
'tested : FreeBasic 1.08.1 with mpfr 4.1.0
'-------------------------------------------
#include "gmp.bi"
#include "mpfr.bi"

dim as mpfr_ptr a = allocate(len(__mpfr_struct))
dim as ulong e2, e10
dim as double tim = TIMER

'decimal precision
e10 = 100

'binary precision
e2 = (1 + e10) / .30103
mpfr_init2 (a, e2)

mpfr_const_euler (a, MPFR_RNDN)
mpfr_printf (!"gamma %.*Rf\n\n", e10, a)

gmp_printf (!"time: %.7f s\n", TIMER - tim)
end

jq

Translated from C (Bailey, 1988)

Works with: jq

Works with gojq, the Go implementation of jq

# Bailey, 1988
def bailey($n; $eps):
  pow(2; $n) as $n2
  | {a :1, b: 0, h: 1, r: 1, k: 1}
  | until( (.b - .a)|fabs <= $eps;
      .k += 1
      | .r *= ($n2 / .k)
      | .h += (1.0 / .k)
      | .b = .a
      | .a += (.r * .h) )
  | (.a * $n2 / ($n2|exp) ) - ($n * (2|log)) ;

Output:

bailey(5; 1E-6)
0.5772156649015341

Julia

Translation of: PARI/GP

display(MathConstants.γ)  # γ = 0.5772156649015...

Mathematica/Wolfram Language

N[EulerGamma, 1000]

Output:

0.57721566490153286060651209008240243104215933593992359880576723488486772677766467093694706329174674
9514631447249807082480960504014486542836224173997644923536253500333742937337737673942792595258247094
9160087352039481656708532331517766115286211995015079847937450857057400299213547861466940296043254215
1905877553526733139925401296742051375413954911168510280798423487758720503843109399736137255306088933
1267600172479537836759271351577226102734929139407984301034177717780881549570661075010161916633401522
7893586796549725203621287922655595366962817638879272680132431010476505963703947394957638906572967929
6010090151251959509222435014093498712282479497471956469763185066761290638110518241974448678363808617
4945516989279230187739107294578155431600500218284409605377243420328547836701517739439870030237033951
8328690001558193988042707411542227819716523011073565833967348717650491941812300040654693142999297779
569303100503086303418569803231083691640025892970890985486825777364288253954925873629596133298574739302

Nim

import std/math

const n = 1e6
var result = 1.0

for i in 2..int(n):
  result += 1/i

echo result - ln(n)

Output:

0.5772161649007153

PARI/GP

built-in:

\l "euler_const.log"
\p 100
print("gamma ", Euler);
\q

Perl

#!/usr/bin/perl

use strict; # https://en.wikipedia.org/wiki/Euler%27s_constant
use warnings;
use List::Util qw( sum );

print sum( map 1 / $_, 1 .. 1e6) - log 1e6, "\n";

Output:

0.577216164900715

Phix

part 1 (max 12dp)

Translation of Perl, with the same accuracy limitation

-- demo\rosetta\Eulers_constant.exw
with javascript_semantics
constant C = sum(sq_div(1,tagset(1e6)))-log(1e6)
printf(1,"gamma %.12f  (max 12d.p. of accuracy)\n",C)

Output:

gamma 0.577216164901  (max 12d.p. of accuracy)

part 2 (first principles)

Translation of C, from first principles.

without js  -- no mpfr_get_d_2exp() in mpfr.js as yet
requires("1.0.2") -- mpfr_get_d_2exp(), mpfr_addmul_si()
include mpfr.e
mpfr u, v, k2;
integer e, e10, e2
atom f
 
//log(x/y) with the Taylor series for atanh(x-y/x+y)
procedure ln(mpfr s, integer x, y)
    mpfr d = u, q = v;
    assert((x-y)==1) 
    mpfr_set_si(s, x+y)
    mpfr_si_div(s, 1, s)            // s = 1 / (x + y)
    mpfr_mul(k2, s, s)              // k2 = s * s
    mpfr_set(d, s)
    integer k = 1
    while true do
        k += 2;
        mpfr_mul(d, d, k2)          // d *= k2
        mpfr_div_si(q, d, k)        // q = d / k
        mpfr_add(s, s, q)           // s += q
        {f,e} = mpfr_get_d_2exp(q)
        if abs(e)>=e2 then exit end if
    end while 
    mpfr_mul_si(s, s, 2)            //s *= 2
end procedure
 
mpfr a, b
integer k, 
        n = 60,     -- (required precision in decimal dp *6/10)
        n2, 
        r = 41,
        s = 30,
        t = 18;

// n = 2^i * 3^j * 5^k
 
// log(n) = r * log(16/15) + s * log(25/24) + t * log(81/80)
 
// solve linear system for r, s, t
//  4 -3 -4| i
// -1 -1  4| j
// -1  2 -1| k
 
//decimal precision
e10 = floor(n/0.6)
//binary precision
e2 = floor((1 + e10) / 0.30103)
 
mpfr_set_default_precision(e2)
{a, b, u, v, k2} = mpfr_inits(5)
 
//Compute log terms
ln(b, 16, 15)  mpfr_mul_si(a, b, r)     // a = r * b
ln(b, 25, 24)  mpfr_addmul_si(a, b, s)  // a += s * b
ln(b, 81, 80)  mpfr_addmul_si(a, b, t)  // a += t * b

mpfr_neg(a, a)          // a = -a
mpfr_set_si(b, 1)       // b = 1
mpfr_set (u, a)
mpfr_set (v, b)
 
k = 0;
n2 = n * n;
mpfr_set_si(k2, 0)      // k2 = k * k (as below)
while true do
    mpfr_add_si(k2, k2, k*2+1)      // k2 += 2k + 1
    k += 1;
 
    mpfr_div(b, b, k2)
    mpfr_mul_si(b, b, n2)           // b = b * n2 / k2
   
    mpfr_div_si(a, a, k)
    mpfr_mul_si(a, a, n2)
    mpfr_add (a, a, b)
    mpfr_div_si(a, a, k)            // a = (a * n2 / k + b) / k
 
    mpfr_add(u, u, a)               // u += a
    mpfr_add(v, v, b)               // v += b
 
    {f,e} = mpfr_get_d_2exp (a)
    if abs(e)>=e2 then exit end if
end while
 
mpfr_div(u, u, v)
string su = mpfr_get_fixed(u,e10)
printf(1,"gamma %s (maxerr. 1e-%d)\n", {su, e10})

Output:

gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467494 (maxerr. 1e-100)

part 3 (the easy way)

without js  -- no mpfr_const_euler() in mpfr.js as yet
requires("1.0.1") -- mpfr_const_euler()
include mpfr.e
mpfr gamma = mpfr_init(0,-100)
mpfr_const_euler(gamma)
printf(1,"gamma %s (mpfr_const_euler)\n",{mpfr_get_fixed(gamma,100)})

(matches part 2 except for the 100th decimal place)

Output:

gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (mpfr_const_euler)

Picat

List comprehension

main =>
  Gamma = 0.57721566490153286060651209008240,
  println(Gamma),
  foreach(N in 1..8)
     G = e(10**N),
     println([n=N,g=G,diff=G-Gamma])
  end.

e(N) = [1.0/I : I in 1..N].sum-log(N).

Output:

0.577215664901533
[n = 1,g = 0.626383160974208,diff = 0.049167496072675]
[n = 2,g = 0.582207331651529,diff = 0.004991666749996]
[n = 3,g = 0.577715581568206,diff = 0.000499916666674]
[n = 4,g = 0.577265664068165,diff = 0.000049999166632]
[n = 5,g = 0.577220664893106,diff = 0.000004999991574]
[n = 6,g = 0.577216164900715,diff = 0.000000499999182]
[n = 7,g = 0.577215714898951,diff = 0.000000049997419]
[n = 8,g = 0.577215669900188,diff = 0.000000004998655]

Loop

e2(N) = E-log(N) =>
  E = 1,
  foreach(I in 2..N)
    E := E + 1/I
  end.

Translation of: Rust

main =>
  Gamma = 0.577215664901532860606512090082402,
  println(gamma=Gamma),
  member(N, 1..23),
  G = gamma(N),
  println([n=N,g=G,diff=G-Gamma]),
  fail,
  nl.

gamma(N) = Gamma =>
  Gamma = 1/2 - 1/3,
  foreach(I in 2..N)
    Power = 2**I,
    Sign = -1,
    Term = 0,
    foreach(Denominator in Power..(2*Power-1))
      Sign := Sign * -1,
      Term := Term + Sign / Denominator
    end,
    Gamma := Gamma + I*Term
  end.

Output:

[n = 1,g = 0.166666666666667,diff = -0.410548998234866]
[n = 2,g = 0.314285714285714,diff = -0.262929950615819]
[n = 3,g = 0.416741591741592,diff = -0.160474073159941]
[n = 4,g = 0.482164184398886,diff = -0.095051480502647]
[n = 5,g = 0.522141654090275,diff = -0.055074010811257]
[n = 6,g = 0.545853770405349,diff = -0.031361894496184]
[n = 7,g = 0.559605750992416,diff = -0.017609913909116]
[n = 8,g = 0.567441138957738,diff = -0.009774525943794]
[n = 9,g = 0.571842107494027,diff = -0.005373557407506]
[n = 10,g = 0.574285301882304,diff = -0.002930363019229]
[n = 11,g = 0.57562856705805,diff = -0.001587097843483]
[n = 12,g = 0.576361123043496,diff = -0.000854541858037]
[n = 13,g = 0.576757887880701,diff = -0.000457777020832]
[n = 14,g = 0.576971520706463,diff = -0.00024414419507]
[n = 15,g = 0.577085964243776,diff = -0.000129700657756]
[n = 16,g = 0.577147000098518,diff = -0.000068664803014]
[n = 17,g = 0.577179425210813,diff = -0.00003623969072]
[n = 18,g = 0.577196591397621,diff = -0.000019073503912]
[n = 19,g = 0.577205651316587,diff = -0.000010013584946]
[n = 20,g = 0.57721041969158,diff = -0.000005245209953]
[n = 21,g = 0.577212923087556,diff = -0.000002741813977]
[n = 22,g = 0.577214234389975,diff = -0.000001430511558]
[n = 23,g = 0.577214919843452,diff = -0.000000745058081]

Processing

Translation of: C

/*********************************************
 Subject: Comparing five methods for
 computing Euler's constant 0.5772...
 // https://rosettacode.org/wiki/Euler%27s_constant_0.5772...
 --------------------------------------------*/
double a, b, h, n2, r, u, v;
float floatA, floatB, floatN2;
int k, k2, m, n;
double eps = 1e-6;

void setup() {
  size(100, 100);  
  noLoop();
}

void draw() {
  println("From the definition, err. 3e-10\n");

  n = 400;

  h = 1;

  for (int k = 2; k <= n; k++) {
    h += 1.0 / k;
  }
  //faster convergence: Negoi, 1997
  a = log(n +.5 + 1.0 / (24*n));

  println("Hn    ", h);
  println("gamma ", h - a);
  println("k = ", n);
  println("");


  println("Sweeney, 1963, err. idem");
  n = 21;

  double s[] = {0, n};
  r = n;
  k = 1;
  while (r > eps) {
    k ++;
    r *= (double) n / k;
    s[k & 1] = s[k & 1] + r / k;
  } 

  // println("gamma %.16f\nk = %d\n\n", s[1] - s[0] - log(n), k);

  println("Hn    ", h);
  println("gamma ", s[1] - s[0] - log(n));
  println("k = ", k);
  println("");

  println("Bailey, 1988");
  n = 5;
  floatA = 1;
  h = 1;
  floatN2 = pow(2, n);
  r = 1;
  k = 1;
  while (abs(floatB - floatA) > eps) {
    k += 1;
    r *= floatN2 / k;
    h += 1.0 / k;
    floatB = floatA; 
    floatA += r * h;
  }
  floatA *= floatN2 / exp(floatN2);

  println("gamma ", floatA - n * log(2));
  println("k = ", k);
  println("");

  println("Brent-McMillan, 1980");

  n = 13;

  floatA = -log(n);
  floatB = 1;
  u = a;
  v = b;
  n2 = n * n;
  k2 = 0;
  k = 0;


  while (abs(floatA) > eps) {
    k2 += 2*k + 1;
    k += 1;
    floatA *= n2 / k;
    floatB *= n2 / k2;
    floatA = (floatA + floatB) / k;
    u += floatA;
    v += floatB;
  } 
  println("gamma  ", u / v);
  println("k      ", k);



  println("How Euler did it in 1735\n");
  //Bernoulli numbers with even indices

  double[] B2 = new double[11]; 

  B2[1] = 1.0;
  B2[2] = 1.0/6;
  B2[3] = -1.0/30;
  B2[4] = 1.0/42;
  B2[5] = -1.0/30;
  B2[6] = 5.0/66;
  B2[7] = -691.0/2730;
  B2[8] = 7.0/6;
  B2[9] = -3617.0/510;
  B2[10]= 43867.0/798;

  m = 7;
  n = 10;

  //n-th harmonic number
  h = 1;
  for (k = 2; k <= n; k++) {
    h += 1.0 / k;
  }
  println("Hn    ", h);

  h -= log(n);
  println("  -ln ", h);

  //expansion C = -digamma(1)
  a = -1.0 / (2*n);
  n2 = n * n;
  r = 1;
  for (k = 1; k <= m; k++) {
    r *= n2;
    a += B2[k] / (2*k * r);
  }

  println("");
  println("err  ", a);
  println("gamma ", h + a );
  println("k = ", n + m);
  println("");
  println("C  =  0.57721566490153286...\n");
}

Output:

From the definition, err. 3e-10

Hn     6.569929751800373
gamma  0.577215823577717
k =  400

Sweeney, 1963, err. idem
Hn     6.569929751800373
gamma  0.5772155784070492
k =  68

Bailey, 1988
gamma  0.5772176
k =  67

Brent-McMillan, 1980
gamma   0.5772157269353247
k       40


How Euler did it in 1735

Hn     2.9289682805538177
  -ln  0.6263831555843353
err   -0.044995839604388355
gamma  0.581387315979947
k =  17

C  =  0.57721566490153286...

Racket

#lang racket/base

(require math/number-theory
         math/base)

gamma.0

;; if you want to work it out the hard way...
(define (H n)
  (for/sum ((i n)) (/ (add1 i))))

(define (g #:n (n 10) #:k (k 7))
  (+ (- (H n)
        (log n)
        (/ (* n 2)))
     (for/sum ((2k (in-range 2 (* 2 (add1 k)) 2)))
       (/ (bernoulli-number 2k) (* (expt n 2k) 2k)))))

(g)

Output:

0.5772156649015329
0.5772156649015324

Raku

# 20211124 Raku programming solution 

sub gamma (\N where N > 1) { # Vacca series https://w.wiki/4ybp
                             # convert terms to FatRat for arbitrary precision
   return  (1/2 - 1/3) + [+] (2..N).race.map: -> \n {

      my ($power, $sign, $term) = 2**n, -1;

      for ($power..^2*$power) { $term += ($sign = -$sign) / $_ }

      n*$term
   }
}

say gamma 23 ;

Output:

0.5772149198434515

Ruby

n = 1e6
p (1..n).sum{ 1.0/_1 } - Math.log(n)

Output:

0.5772161649014507 #12 digits accurate

Rust

Translation of: Raku

// 20220322 Rust programming solution

fn gamma(N: u32) -> f64 { // Vacca series https://w.wiki/4ybp

    return 1f64 / 2f64 - 1f64 / 3f64
        + ((2..=N).map(|n| {
            let power: u32 = 2u32.pow(n);
            let mut sign: f64 = -1f64;
            let mut term: f64 = 0f64;

            for denominator in power..=(2 * power - 1) {
                sign *= -1f64;
                term += sign / f64::from(denominator);
            }

            return f64::from(n) * term;
        }))
        .sum::<f64>();
}

fn main() {
    println!("{}", gamma(23));
}

Output:

0.5772149198434514

Scheme

Works with: Chez Scheme

; Procedure to compute factorial.
(define fact
  (lambda (n)
    (if (<= n 0)
      1
      (* n (fact (1- n))))))

; Compute Euler's gamma constant as the difference of log(n) from a sum.
; See section 2.3 of <http://numbers.computation.free.fr/Constants/Gamma/gamma.html>.
(define gamma
  (lambda (n)
    (let ((sum 0))
      (do ((k 1 (1+ k)))
          ((> k (* 3.5911 n)) (- sum (log n)))
        (set! sum (+ sum (/ (* (expt -1 (1- k)) (expt n k)) (* k (fact k)))))))))

; Show Euler's gamma constant computed at log(100).
(printf "Euler's gamma constant: ~a~%" (gamma 100))

Output:

Euler's gamma constant: 0.5772156649015328

Sidef

Built-in:

# 100 decimals of precision
local Num!PREC = 4*100
say Num.EulerGamma

Output:

0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495

Several formulas:

const n = (ARGV ? Num(ARGV[0]) : 50)       # number of iterations

define ℯ = Num.e
define π = Num.pi
define γ = Num.EulerGamma

func display(r, t) {
    say "#{r}\terror: #{ '%.0g' % abs(r - t) }"
}

# Original definition of the Euler-Mascheroni constant, due to Euler (1731)
display(sum(1..n, {|n| 1/n }) - log(n), γ)

# Formula due to Euler (best convergence)
display(harmfrac(n) - log(n) - 1/(2*n) - sum(1..n, {|k|
    -bernoulli(2*k) / (2*k) / n**(2*k)
}), γ)

# Formula derived from the above formula of Euler,
# using approximations of Bernoulli numbers.
display(harmfrac(n) - log(n) - 1/(2*n) - sum(1..n, {|k|
    (-1)**k * 4 * sqrt(π*k) * (π * ℯ)**(-2*k) * k**(2*k) / (2*k) / n**(2*k)
}), γ)

# Euler-Mascheroni constant, involving zeta(n)
display(1 - sum(2..(n+1), {|n|
    (zeta(n) - 1) / n
}), γ)

# Limit_{n->Infinity} zeta((n+1)/n) - n} = gamma
display(zeta((n+1)/n) - n, γ)

# Series due to Euler (1731).
display(sum(2..(n+1), {|n|
    (-1)**n * zeta(n) / n
}),  γ)

# Formula due to Euler in terms of log(2) and the odd zeta values
display(3/4 - log(2)/2 + sum(1..n, {|n|
    (1 - 1/(2*n + 1)) * (zeta(2*n + 1) - 1)
}), γ)

# Formula due to Euler in terms of log(2) and the odd zeta values (VII)
display(log(2) - sum(1..n, {|n|
    zeta(2*n + 1) / (2*n + 1) / 2**(2*n)
}), γ)

# Formula due to Vacca (1910)
display(sum(1..n, {|n|
    (-1)**n * floor(log2(n)) / n
}), γ)

Output:

0.58718233290127899894172100505421724484389898107	error: 0.01
0.57721566490153286060651209008240243104215933594	error: 2e-58
0.577201775274185974649592917416402750312879661543	error: 1e-05
0.577215664901532868991217643213156967011395887777	error: 8e-18
0.57867004101560321761330253540741574969540128177	error: 0.001
0.567507841748305076772446986005418728718501189232	error: 0.01
0.577215664901532860606512090082272222693164663104	error: 1e-31
0.57721566490153286060651209008240496797924366087	error: 3e-33
0.611009392556929160631547597803236563977259982583	error: 0.03

Vlang

Translation of: C

import math
const eps = 1e-6
fn main() {
    //.5772
    println("From the definition, err. 3e-10")
    mut n := 400
    mut h := 1.0
    for k in 2..n+1 {
        h += 1.0/f64(k)
    }
    //faster convergence: Negoi, 1997
    mut a := math.log(f64(n) + 0.5 + 1.0/f64(24*n))
    
    println("Hn    ${h:0.16f}")
    println("gamma ${h-a:0.16f}\nk = $n\n")
    
    println("Sweeney, 1963, err. idem")
    n = 21
    mut s := [0.0, f64(n)]
    mut r := f64(n)
    mut k := 1
    for {
        k++
        r *= f64(n) / f64(k)
        s[k & 1] += r/f64(k)
        if r <= eps {
            break
        }
    }
    println("gamma ${s[1] - s[0] - math.log(n):0.16f}\nk = $k\n")
    
    println("Bailey, 1988")
    n = 5
    a = 1.0
    h = 1.0
    mut n2 := math.pow(f64(2),f64(n))
    r = 1
    k = 1
    for {
        k++
        r *= n2 / f64(k)
        h += 1/f64(k)
        b := a
        a += r * h
        if math.abs(b-a) <= eps {
            break
        }
    }
    a *= n2 / math.exp(n2)
    println("gamma ${a - n * math.log(2):.16f}\nk = $k\n")
    
    println("Brent-McMillan, 1980")
    n = 13
    a = -math.log(n)
    mut b := 1.0
    mut u := a
    mut v := b
    n2 = n * n
    mut k2 := 0
    k = 0
    for {
        k2 += 2*k + 1
        k++
        a *= n2 / f64(k)
        b *= n2 / f64(k2)
        a = (a + b)/f64(k)
        u += a
        v += b
        if math.abs(a) <= eps {
            break
        }
    }
    println("gamma ${u/v:0.16f}\nk = $k\n")
    
    println("How Euler did it in 1735")
    // Bernoulli numbers with even indices
    b2 := [1.0, 1.0/6, -1.0/30, 1.0/42, -1.0/30, 5.0/66, -691.0/2730, 7.0/6, -3617.0/510, 43867.0/798]
    m := 7
    n = 10
    // n'th harmonic number
    h = 1.0
    for kz in 2..n+1 {
        h += 1.0/f64(kz)
    } 
    println("Hn    ${h:0.16f}")
    h -= math.log(n)
    println("  -ln ${h:0.16f}")
    // expansion C = -digamma(1)
    a = -1.0 / (2.0*f64(n))
    n2 = f64(n * n)
    r = 1
    for kq in 1..m+1 {
        r *= n2
        a += b2[kq] / (2.0*f64(kq)*r)
    }
    println("err  ${a:0.16f}\ngamma ${h+a:0.16f}\nk = ${n+m}") 
    println("\nC = 0.57721566490153286...")
}

Output:

Same as C entry

Wren

Translation of: C

Single precision (Cli)

Library: Wren-fmt

Note that, whilst internally double arithmetic is carried out to the same precision as C (Wren is written in C), printing doubles is effectively limited to a maximum of 14 decimal places.

import "./fmt" for Fmt

var eps = 1e-6

System.print("From the definition, err. 3e-10")
var n = 400
var h = 1
for (k in 2..n) h = h + 1/k
//faster convergence: Negoi, 1997
var a = (n + 0.5 + 1/(24*n)).log

Fmt.print("Hn    $0.14f", h)
Fmt.print("gamma $0.14f\nk = $d\n", h - a, n)

System.print("Sweeney, 1963, err. idem")
n = 21
var s = [0, n]
var r = n
var k = 1
while (true) {
    k = k + 1
    r = r * n / k
    s[k & 1] = s[k & 1] + r/k
    if (r <= eps) break
}
Fmt.print("gamma $0.14f\nk = $d\n", s[1] - s[0] - n.log, k)

System.print("Bailey, 1988")
n = 5
a = 1
h = 1
var n2 = 2.pow(n)
r = 1
k = 1
while (true) {
    k = k + 1
    r = r * n2 / k
    h = h + 1/k
    var b = a
    a = a + r * h
    if ((b-a).abs <= eps) break
}
a = a * n2 / n2.exp
Fmt.print("gamma $0.14f\nk = $d\n", a - n * 2.log, k)

System.print("Brent-McMillan, 1980")
n = 13
a = -n.log
var b = 1
var u = a
var v = b
n2 = n * n
var k2 = 0
k = 0
while (true) {
    k2 = k2 + 2*k + 1
    k = k + 1
    a = a * n2 / k
    b = b * n2 / k2
    a = (a + b)/k
    u = u + a
    v = v + b
    if (a.abs <= eps) break
}
Fmt.print("gamma $0.14f\nk = $d\n", u / v, k)

System.print("How Euler did it in 1735")
// Bernoulli numbers with even indices
var b2 = [1, 1/6, -1/30, 1/42, -1/30, 5/66, -691/2730, 7/6, -3617/510, 43867/798]
var m = 7
n = 10
// n'th harmonic number
h = 1
for (k in 2..n) h = h + 1/k
Fmt.print("Hn    $0.14f", h)
h = h - n.log
Fmt.print("  -ln $0.14f", h)
// expansion C = -digamma(1)
a = -1 / (2*n)
n2 = n * n
r = 1
for (k in 1..m) {
    r = r * n2
    a = a + b2[k] / (2*k*r)
}
Fmt.print("err  $0.14f\ngamma $0.14f\nk = $d", a, h + a, n + m) 
System.print("\nC = 0.57721566490153286...")

Output:

From the definition, err. 3e-10
Hn    6.56992969117651
gamma 0.57721566457657
k = 400

Sweeney, 1963, err. idem
gamma 0.57721566456363
k = 68

Bailey, 1988
gamma 0.57721566490154
k = 89

Brent-McMillan, 1980
gamma 0.57721566490153
k = 40

How Euler did it in 1735
Hn    2.92896825396825
  -ln 0.62638316097421
err  -0.04916749607268
gamma 0.57721566490153
k = 17

C = 0.57721566490153286...

Multi precision (Embedded)

Library: Wren-gmp

The display is limited to 100 digits for all four examples as I couldn't see much point in showing them all.

import "./gmp" for Mpf

var euler = Fn.new { |n, r, s, t|
    // decimal precision
    var e10 = (n/0.6).floor

    // binary precision
    var e2 = ((1 + n/0.6)/0.30103).round
    Mpf.defaultPrec = e2

    var b = Mpf.new().log(Mpf.from(16).div(15))
    var a = b.mul(r)
    b = Mpf.new().log(Mpf.from(25).div(24))
    a.add(b.mul(s))
    b = Mpf.new().log(Mpf.from(81).div(80))
    var u = b * t
    a.add(u).neg
    b.set(1)
    u.set(a)
    var v = Mpf.from(b)
    var k = 0
    var n2 = n * n
    var k2 = Mpf.zero
    while (true) {
        k2.add((k << 1) + 1)
        k = k + 1
        b.mul(n2).div(k2)
        a.mul(n2).div(k).add(b).div(k)
        u.add(a)
        v.add(b)
        var e = Mpf.frexp(a)[1]
        if (e.abs >= e2) break
    }
    u.div(v)
    System.print("gamma %(u.toString(10, 100)) (maxerr. 1e-%(e10))")
    System.print("k = %(k)")
}

var start = System.clock
euler.call(60, 41, 30, 18)
euler.call(4800, 85, 62, 37)
euler.call(9375, 91, 68, 40)
euler.call(18750, 98, 73, 43)
System.print("\nTook %(System.clock - start) seconds.")

Output:

gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-100)
k = 255
gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-8000)
k = 20462
gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-15625)
k = 39967
gamma 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495 (maxerr. 1e-31250)
k = 79936

Took 2.330538 seconds.

The easy way (Embedded)

import "./gmp" for Mpf

var prec = (101/0.30103).round
var gamma = Mpf.euler(prec)
System.print(gamma.toString(10, 100))

Output:

0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495