# How to make a heat map using three variables?

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Danny Helwegen on 13 Oct 2020
Commented: Danny Helwegen on 14 Oct 2020
Hey,
I have an equation calculating the concentration depending on 2 variables (r and theta). I want to make a plot of r vs. theta that shows the concentration at certain points (e.g. for the axis x => r, y=> theta, z => concentration).
I used the following code to calculate the values and generate a matrix A containing the concentration at different r and theta values.
c_1 = 0.5;
R = 10^(-3);
N = 100;
theta = linspace(0,pi/2,N);
r = linspace(0,R,N);
for i = 1:1:N
for j = 1:1:N
A(i,j) = c_1 .* (r(i)./R) .* cos(theta(j));
end
end
The matrix A has (of course) the dimensions N x N. But I don't really know how to make a nice plot for this. Can anyone help me?
Kind regards,
Danny

KSSV on 13 Oct 2020
Edited: KSSV on 14 Oct 2020
c_1 = 0.5;
R = 10^(-3);
N = 100;
theta = linspace(0,pi/2,N);
r = linspace(0,R,N);
[r,theta] = meshgrid(r,theta) ;
A = c_1*(r/R).*cos(theta);
pcolor(r,theta,A)
colorbar
Danny Helwegen on 14 Oct 2020
Thanks for your help, it works