Gaussian primes
A Gaussian Integer is a complex number such that its real and imaginary parts are both integers.
a + bi where a and b are integers and i is √-1.
The norm of a Gaussian integer is its product with its conjugate.
N(a + bi) = (a + bi)(a − bi) = a² + b²
A Gaussian integer is a Gaussian prime if and only if either its norm is a prime number, or it is the product of a unit (±1, ±i) and a prime number of the form 4n + 3.
Prime integers that are not of the form 4n + 3 can be factored into a Gaussian integer and its complex conjugate so are not a Gaussian prime.
E.G. 5 = (2 + i)(2 − i) So 5 is not a Gaussian prime
Gaussian primes are octogonally symmetrical on a real / imaginary Cartesian field. If a particular complex norm a² + b² is prime, then the additive inverse b² + a² is also prime, as are the complex conjugates and multiplicative inverses of both.
- Task
Find and show, here on this page, the Gaussian primes with a norm of less than 100, (within a radius of 10 from the origin 0 + 0i on a complex plane.)
Plot the points corresponding to the Gaussian primes on a Cartesian real / imaginary plane at least up to a radius of 50.
- See also
J
Implementation: <lang J>isgpri=: {{
if. 1 p: (*+) y do. 1 return. end.
int=. |(+.y)-.0
if. 1=#int do. {.(1 p: int) * 3=4|int else. 0 end.
}}"0</lang>
Plot of gaussian primes up to radius 50: <lang J> 1j1#"1'#' (<"1]50++.(#~ isgpri * 50>:|) ,j./~i:100)} '+' (<50 50)} '|' 50}"1 '-' 50} 100 100$' '
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</lang>
Gaussian primes less than radius 10 (sorted by radius):<lang J> 10 10$(/: |)(#~ isgpri * 10>|) ,j./~i:10 _1j_1 _1j1 1j_1 1j1 _2j_1 _2j1 _1j_2 _1j2 1j_2 1j2
2j_1 2j1 _3 0j_3 0j3 3 _3j_2 _3j2 _2j_3 _2j3 2j_3 2j3 3j_2 3j2 _4j_1 _4j1 _1j_4 _1j4 1j_4 1j4 4j_1 4j1 _5j_2 _5j2 _2j_5 _2j5 2j_5 2j5 5j_2 5j2
_6j_1 _6j1 _1j_6 _1j6 1j_6 1j6 6j_1 6j1 _5j_4 _5j4 _4j_5 _4j5 4j_5 4j5 5j_4 5j4 _7 0j_7 0j7 7 _7j_2 _7j2 _2j_7 _2j7 2j_7 2j7 7j_2 7j2 _6j_5 _6j5 _5j_6 _5j6 5j_6 5j6 6j_5 6j5 _8j_3 _8j3 _3j_8 _3j8
3j_8 3j8 8j_3 8j3 _8j_5 _8j5 _5j_8 _5j8 5j_8 5j8 8j_5 8j5 _9j_4 _9j4 _4j_9 _4j9 4j_9 4j9 9j_4 9j4</lang>
Raku
Plotting the points up to a radius of 150. <lang perl6>use List::Divvy;
my @next = { :x(1), :y(1), :2n },;
sub next-interval (Int $int) {
@next.append: (^$int).map: { %( :x($int), :y($_), :n($int² + .²) ) };
@next = |@next.sort: *.<n>;
}
my @gaussian = lazy gather {
my $interval = 1;
loop {
my @this = @next.shift;
@this.push: @next.shift while @next and @next[0]<n> == @this[0]<n>;
for @this {
.take if .<n>.is-prime || (!.<y> && .<x>.is-prime && (.<x> - 3) %% 4);
next-interval(++$interval) if $interval == .<x>
}
}
}
- Primes within a radius of 10 from origin
say "Gaussian primes with a norm less than 100 sorted by norm:"; say @gaussian.&before(*.<n> > 10²).map( {
my (\i, \j) = .<x>, .<y>;
flat ((i,j),(-i,j),(-i,-j),(i,-j),(j,i),(-j,i),(-j,-i),(j,-i)).map: {
.[0] ?? .[1] ?? (sprintf "%d%s%di", .[0], (.[1] >= 0 ?? '+' !! ), .[1]) !! .[0] !! "{.[1]}i"
}} )».subst('1i', 'i', :g)».fmt("%6s")».unique.flat.batch(10).join: "\n" ;
- Plot points within a 150 radius
use SVG;
my @points = unique flat @gaussian.&before(*.<n> > 150²).map: {
my (\i, \j) = .<x>, .<y>;
do for (i,j),(-i,j),(-i,-j),(i,-j),(j,i),(-j,i),(-j,-i),(j,-i) {
:use['xlink:href'=>'#point', 'transform'=>"translate({500 + 3 * .[0]},{500 + 3 * .[1]})"]
}
}
'gaussian-primes-raku.svg'.IO.spurt: SVG.serialize(
svg => [
:width<1000>, :height<1000>,
:rect[:width<100%>, :height<100%>, :style<fill:black;>],
:defs[:g[:id<point>, :circle[ :cx(0), :cy(0), :r("2"), :fill('gold') ]]],
|@points
],
);</lang>
- Output:
Gaussian primes with a norm less than 100 sorted by norm: 1+i -1+i -1-i 1-i 2+i -2+i -2-i 2-i 1+2i -1+2i -1-2i 1-2i 3 -3 3i -3i 3+2i -3+2i -3-2i 3-2i 2+3i -2+3i -2-3i 2-3i 4+i -4+i -4-i 4-i 1+4i -1+4i -1-4i 1-4i 5+2i -5+2i -5-2i 5-2i 2+5i -2+5i -2-5i 2-5i 6+i -6+i -6-i 6-i 1+6i -1+6i -1-6i 1-6i 5+4i -5+4i -5-4i 5-4i 4+5i -4+5i -4-5i 4-5i 7 -7 7i -7i 7+2i -7+2i -7-2i 7-2i 2+7i -2+7i -2-7i 2-7i 6+5i -6+5i -6-5i 6-5i 5+6i -5+6i -5-6i 5-6i 8+3i -8+3i -8-3i 8-3i 3+8i -3+8i -3-8i 3-8i 8+5i -8+5i -8-5i 8-5i 5+8i -5+8i -5-8i 5-8i 9+4i -9+4i -9-4i 9-4i 4+9i -4+9i -4-9i 4-9i
Off-site SVG image: gaussian-primes-raku.svg
