# Plot the Gaussian Distribution in 3D

In probability theory, the normal (or Gaussian) distribution is a very common continuous probability distribution. Normal distributions are important in statistics and are often used in the natural and social sciences to represent real-valued random variables whose distributions are not known.

## The challenge

Your challenge is to plot the probability density of the Gaussian Distribution on a 3-dimensional plane. This function is defined as:

Where:

A = 1, σx = σy = σ

## Rules

• Your program must take one input σ, the standard deviation.
• Your program must print a 3D plot of the Gaussian Distribution in the highest quality as your language/system allows.
• Your program may not use a direct Gaussian Distribution or probability density builtin.
• Your program does not have to terminate.
• Your plot may be in black and white or color.
• Your plot must have grid lines on the bottom. Grid lines on the sides (as shown in the examples) are unnecessary.
• Your plot does not need to have line numbers next to the grid lines.

## Scoring

As usual in , the submission with the least bytes wins! I may never "accept" an answer using the button, unless one is incredibly small and intuitive.

## Example output

Your output could look something like this:

Or it could look like this:

• I was confused that you just showed the function for the X-axis. Do we need to take separate input/outputs for the X and Y sigma and mu's? – Scott Milner May 27 '17 at 2:00
• So are we to assume that μ equals 0? And what scale do you require for x and y? If the x-and y-ranges are chosen very small relative to σ, then the graph will essentially look like a constant function. – Greg Martin May 27 '17 at 2:32
• (For the two-dimensional distribution, I think it is clearer if you use |x-μ|^2 in the definition rather than (x-μ)^2.) – Greg Martin May 27 '17 at 2:33
• @GregMartin Edited. – MD XF May 27 '17 at 3:03
• Still not clear ... what are x_o and y_o and θ? – Greg Martin May 27 '17 at 4:28

# Gnuplot 4, 64626160 47 bytes

(Tied with Mathematica! WooHoo!)

se t pn;se is 80;sp exp(-(x**2+y**2)/(2*$0**2))  Save the above code into a file named A.gp and invoke it with the following: gnuplot -e 'call "A.gp"$1'>GnuPlot3D.png

where the $1 is to be replaced with the value of σ. This will save a .png file named GnuPlot3D.png containing the desired output into the current working directory. Note that this only works with distributions of Gnuplot 4 since in Gnuplot 5 the $n references to arguments were deprecated and replaced with the unfortunately more verbose ARGn.

Sample output with σ = 3:

This output is fine according to OP.

# Gnuplot 4, Alternate Solution, 60 bytes

Here is an alternate solution which is much longer than the previous one but the output looks much better in my opinion.

se t pn;se is 80;se xyp 0;sp exp(-(x**2+y**2)/(2*\$0**2))w pm


This still requires Gnuplot 4 for the same reason as the previous solution.

Sample output with σ = 3:

• I am not sure if it molds to the specifications required what specifications do you think it does not meet? – MD XF May 29 '17 at 0:27
• @MDXF Firstly, I am not sure if the transparency of the graph is okay. I honestly don't really like it, which is why I was not sure if it would be okay here. Secondly, the graph begins one unit high from the bottom by default, and I am not sure if that is all right either. Thirdly, because the graph begins one unit high, I am not sure the disproportionality of the graph compared to the graphs given in the original post is all right. However, if this is all okay with you, I will happily make it the main answer. – R. Kap May 29 '17 at 6:23
• @MDXF In fact, I was going to post it as the original answer, but for these reasons I chose not to and posted by current answer instead. – R. Kap May 29 '17 at 6:24
• @MDXF Actually, I can make it even shorter if this is okay. I understand if it won't be, but it does not hurt to ask. It is the default way Gnuplot would plot the probability density of the Gaussian distribution with a Sigma of 2 without any environment modifications. – R. Kap May 29 '17 at 6:33
• @MDXF I guess I could have asked before posting my original answer, but at the time I was very eager to post an answer. – R. Kap May 29 '17 at 9:06

# C++, 3477 3344 bytes

Byte count does not include the unnecessary newlines.
MD XF golfed off 133 bytes.

There's no way C++ can compete for this, but I thought it would be fun to write a software renderer for the challenge. I tore out and golfed some chunks of GLM for the 3D math and used Xiaolin Wu's line algorithm for rasterization. The program outputs the result to a PGM file named g.

#include<array>
#include<cmath>
#include<vector>
#include<string>
#include<fstream>
#include<algorithm>
#include<functional>
#define L for
#define A auto
#define E swap
#define F float
#define U using
U namespace std;
#define K vector
#define N <<"\n"
#define Z size_t
#define R return
#define B uint8_t
#define I uint32_t
#define P operator
#define W(V)<<V<<' '
#define Y template<Z C>
#define G(O)Y vc<C>P O(vc<C>v,F s){vc<C>o;L(Z i=0;i<C;++i){o\
[i]=v[i]O s;}R o;}Y vc<C>P O(vc<C>l, vc<C>r){vc<C>o;L(Z i=0;i<C;++i){o[i]=l[i]O r[i];}R o;}
Y U vc=array<F,C>;U v2=vc<2>;U v3=vc<3>;U v4=vc<4>;U m4=array<v4,4>;G(+)G(-)G(*)G(/)Y F d(
vc<C>a,vc<C>b){F o=0;L(Z i=0;i<C;++i){o+=a[i]*b[i];}R o;}Y vc<C>n(vc<C>v){R v/sqrt(d(v,v));
}v3 cr(v3 a,v3 b){R v3{a[1]*b[2]-b[1]*a[2],a[2]*b[0]-b[2]*a[0],a[0]*b[1]-b[0]*a[1]};}m4 P*(
m4 l,m4 r){R{l[0]*r[0][0]+l[1]*r[0][1]+l[2]*r[0][2]+l[3]*r[0][3],l[0]*r[1][0]+l[1]*r[1][1]+
l[2]*r[1][2]+l[3]*r[1][3],l[0]*r[2][0]+l[1]*r[2][1]+l[2]*r[2][2]+l[3]*r[2][3],l[0]*r[3][0]+
l[1]*r[3][1]+l[2]*r[3][2]+l[3]*r[3][3]};}v4 P*(m4 m,v4 v){R v4{m[0][0]*v[0]+m[1][0]*v[1]+m[
2][0]*v[2]+m[3][0]*v[3],m[0][1]*v[0]+m[1][1]*v[1]+m[2][1]*v[2]+m[3][1]*v[3],m[0][2]*v[0]+m[
1][2]*v[1]+m[2][2]*v[2]+m[3][2]*v[3],m[0][3]*v[0]+m[1][3]*v[1]+m[2][3]*v[2]+m[3][3]*v[3]};}
m4 at(v3 a,v3 b,v3 c){A f=n(b-a);A s=n(cr(f,c));A u=cr(s,f);A o=m4{1,0,0,0,0,1,0,0,0,0,1,0,
0,0,0,1};o[0][0]=s[0];o[1][0]=s[1];o[2][0]=s[2];o[0][1]=u[0];o[1][1]=u[1];o[2][1]=u[2];o[0]
[2]=-f[0];o[1][2]=-f[1];o[2][2]=-f[2];o[3][0]=-d(s,a);o[3][1]=-d(u,a);o[3][2]=d(f,a);R o;}
m4 pr(F f,F a,F b,F c){F t=tan(f*.5f);m4 o{};o[0][0]=1.f/(t*a);o[1][1]=1.f/t;o[2][3]=-1;o[2
][2]=c/(b-c);o[3][2]=-(c*b)/(c-b);R o;}F lr(F a,F b,F t){R fma(t,b,fma(-t,a,a));}F fp(F f){
R f<0?1-(f-floor(f)):f-floor(f);}F rf(F f){R 1-fp(f);}struct S{I w,h; K<F> f;S(I w,I h):w{w
},h{h},f(w*h){}F&P[](pair<I,I>c){static F z;z=0;Z i=c.first*w+c.second;R i<f.size()?f[i]:z;
}F*b(){R f.data();}Y vc<C>n(vc<C>v){v[0]=lr((F)w*.5f,(F)w,v[0]);v[1]=lr((F)h*.5f,(F)h,-v[1]
);R v;}};I xe(S&f,v2 v,bool s,F g,F c,F*q=0){I p=(I)round(v[0]);A ye=v[1]+g*(p-v[0]);A xd=
rf(v[0]+.5f);A x=p;A y=(I)ye;(s?f[{y,x}]:f[{x,y}])+=(rf(ye)*xd)*c;(s?f[{y+1,x}]:f[{x,y+1}])
+=(fp(ye)*xd)*c;if(q){*q=ye+g;}R x;}K<v4> g(F i,I r,function<v4(F,F)>f){K<v4>g;F p=i*.5f;F
q=1.f/r;L(Z zi=0;zi<r;++zi){F z=lr(-p,p,zi*q);L(Z h=0;h<r;++h){F x=lr(-p,p,h*q);g.push_back
(f(x,z));}}R g;}B xw(S&f,v2 b,v2 e,F c){E(b[0],b[1]);E(e[0],e[1]);A s=abs(e[1]-b[1])>abs
(e[0]-b[0]);if(s){E(b[0],b[1]);E(e[0],e[1]);}if(b[0]>e[0]){E(b[0],e[0]);E(b[1],e[1]);}F yi=
0;A d=e-b;A g=d[0]?d[1]/d[0]:1;A xB=xe(f,b,s,g,c,&yi);A xE=xe(f,e,s,g,c);L(I x=xB+1;x<xE;++
x){(s?f[{(I)yi,x}]:f[{x,(I)yi}])+=rf(yi)*c;(s?f[{(I)yi+1,x}]:f[{x,(I)yi+1}])+=fp(yi)*c;yi+=
g;}}v4 tp(S&s,m4 m,v4 v){v=m*v;R s.n(v/v[3]);}main(){F l=6;Z c=64;A J=g(l,c,[](F x,F z){R
v4{x,exp(-(pow(x,2)+pow(z,2))/(2*pow(0.75f,2))),z,1};});I w=1024;I h=w;S s(w,h);m4 m=pr(
1.0472f,(F)w/(F)h,3.5f,11.4f)*at({4.8f,3,4.8f},{0,0,0},{0,1,0});L(Z j=0;j<c;++j){L(Z i=0;i<
c;++i){Z id=j*c+i;A p=tp(s,m,J[id]);A dp=[&](Z o){A e=tp(s,m,J[id+o]);F v=(p[2]+e[2])*0.5f;
xw(s,{p[0],p[1]},{e[0],e[1]},1.f-v);};if(i<c-1){dp(1);}if(j<c-1){dp(c);}}}K<B> b(w*h);L(Z i
=0;i<b.size();++i){b[i]=(B)round((1-min(max(s.b()[i],0.f),1.f))*255);}ofstream f("g");f
W("P2")N;f W(w)W(h)N;f W(255)N;L(I y=0;y<h;++y){L(I x=0;x<w;++x)f W((I)b[y*w+x]);f N;}R 0;}

• l is the length of one side of the grid in world space.
• c is the number of vertices along each edge of the grid.
• The function that creates the grid is called with a function that takes two inputs, the x and z (+y goes up) world space coordinates of the vertex, and returns the world space position of the vertex.
• w is the width of the pgm
• h is the height of the pgm
• m is the view/projection matrix. The arguments used to create m are...
• field of view in radians
• aspect ratio of the pgm
• near clip plane
• far clip plane
• camera position
• camera target
• up vector

The renderer could easily have more features, better performance, and be better golfed, but I've had my fun!

# Mathematica, 47 bytes

Plot3D[E^(-(x^2+y^2)/2/#^2),{x,-6,6},{y,-6,6}]&


takes as input σ

Input

[2]

output

-2 bytes thanks to LLlAMnYP

• Mathematica winning? No surprises there :P – MD XF May 28 '17 at 0:50
• Saving 2 bytes with E^(-(x^2+y^2)/2/#^2) – LLlAMnYP May 29 '17 at 7:54

# R, 10510287 86 bytes

s=scan();plot3D::persp3D(z=sapply(x<-seq(-6,6,.1),function(y)exp(-(y^2+x^2)/(2*s^2))))


Takes Sigma from STDIN. Creates a vector from -6 to 6 in steps of .1 for both x and y, then creates an 121x121 matrix by taking the outer product of x and y. This is shorter than calling matrix and specifying the dimensions. The matrix is now already filled, but that's ok, because we are overwriting that.

The for-loop loops over the values in x, making use of the vectorized operations in R, creating the density matrix one row at a time.

(s)apply again is a shorter method for vectorized operations. Like the hero it is, it handles the creation of the matrix all by itself, saving quite a few bytes.

## 128125110 109 bytes, but way more fancy:

This plot is created by the plotly package. Sadly the specification is a bit wordy, so this costs a lot of bytes. The result is really really fancy though. I would highly recommend trying it out for yourself.

s=scan();plotly::plot_ly(z=sapply(x<-seq(-6,6,.1),function(y)exp(-(y^2+x^2)/(2*s^2))),x=x,y=x,type="surface")


• I specified in the question that the graph does not need to have line numbers, your second submission is fine. – MD XF May 27 '17 at 14:13
• Oh, I must've missed that. I swapped my solutions around. I think the plotly plot is fancy enough to warrant still being included here. – JAD May 27 '17 at 15:46
• Well, both are much, much fancier than mine :P – MD XF May 28 '17 at 0:51
• Since you only use s once, could you do 2*scan()^2 and remove the s=scan(); at the start? It would save 3 bytes. – KSmarts Sep 29 '17 at 14:49

# Applesoft BASIC, 930783782727719702695 637 bytes

-72 bytes and a working program thanks to ceilingcat spotting my error and a shortened algorithm

0TEXT:HOME:INPUTN:HGR:HCOLOR=3:W=279:H=159:L=W-100:Z=L/10:B=H-100:C=H-60:K=0.5:M=1/(2*3.14159265*N*N):FORI=0TO10STEPK:X=10*I+1:Y=10*I+B:HPLOTX,Y:FORJ=0TOL STEP1:O=10*J/L:D=ABS(5-I):E=ABS(5-O):R=(D*D+E*E)/(2*N*N):G=EXP(-R)*M:A=INT((C*G)/M):X=10*I+Z*O+1:Y=10*I+B-A:HPLOTTOX,Y:IF(I=0)GOTO4
1IF(J=L)GOTO3
2V=INT(J/10):IF((J/10)<>V)GOTO5
3D=ABS(5-I+K):E=ABS(5-O):R=(D*D+E*E)/(2*N*N):U=EXP(-R)/(2*3.14159*N*N):S=INT((C*U)/M):P=10*(I-K)+Z*O+1:Q=10*(I-K)+B-S:HPLOT TOP,Q:HPLOTX,Y
4IF(J=0)GOTO7:IF(I<10)GOTO5:IF(J=L)GOTO6:V=INT(J/10):IF((J/10)=V)GOTO6
5HCOLOR=0
6HPLOTTOX,10*I+B:HCOLOR=3:HPLOTX,Y
7NEXTJ:NEXTI:HPLOTW+1,H:HPLOTTO101,H:HPLOTTO0+1,H


Ungolfed version here.

When given input 1:

When given input 2:

• This yet again shows the superiority of BASIC .... – user9206 May 29 '17 at 7:20
• Can save a few more bytes by setting one or more variables to some frequently used value, such as 10. Also, suggest replacing EXP(X)/(2*3.14159*S1*S1) with EXP(X)*M – ceilingcat Jun 5 '17 at 21:37