countourf doesn't show colored regions in Matlab

Question

What should I change in my code that countorf shows regions with more color differences?

clear all;
close all;
phi=90;
[xx,yy] = meshgrid(-20:0.1:20,-20:0.1:20);
Idontwantthis = (xx.^2+yy.^2)<0.1;
u = (xx./(xx.^2+yy.^2).^(3/2));
v = (yy./(xx.^2+yy.^2).^(3/2));
data= sqrt(u.^2+v.^2);
data(Idontwantthis)=NaN;
u(Idontwantthis)=NaN;
v(Idontwantthis)=NaN;
contourf(xx,yy,data,20);

Answer 1

First, you don't need meshgrid over [-20 20]. Try reducing the range to like [-2 2]. After you run contourf, change colormap:

clear all;
close all;
phi=90;

[xx,yy] = meshgrid(-2:0.01:2,-2:0.01:2);

Idontwantthis = (xx.^2+yy.^2)<0.1;
u = (xx./(xx.^2+yy.^2).^(3/2));
v = (yy./(xx.^2+yy.^2).^(3/2));
data= sqrt(u.^2+v.^2);
data(Idontwantthis)=NaN;
u(Idontwantthis)=NaN;
v(Idontwantthis)=NaN;

contourf(xx,yy,data,20);
colormap hsv;

This is what your result will look like:

Hope that helps!