Stop contourf from interpolating between my grid

I am using a contourf plot of the form: contourf(B0, B1, Z)

The spacing of B0 and B1 is .05.

The function values in Z only take on a few discrete values.

The resulting behavior is that if say Z(b0,b1) = 1 and Z(b0+1,b1) = 2, then MATLAB draws many contours between the two points, thereby creating many lines between the two points.

Is there a way to prevent this behavior?

My initial thought was to try to specify the number of contours directly. However, when this is done MATLAB just fills the region between the two points with one of the other colors being used, which is also not appropriate.

[Walter Roberson]

What is the form of Z? Is it a scalar, a vector of sorted values, an array?

Answer 1

[even coil]

Turns out the pcolor command works for what I want.

colormap(gray(length(unique(Z))));
h = pcolor(B0,B1,Z);
caxis([-.5 1]);
xlim([-.2 1.6]);
ylim([-1 1]);
set(h, 'EdgeColor', 'none');

Answer 2

[Walter Roberson]

If your Z is an array then you are using the contourf(X,Y,Z) form, and you instead want to use the contourf(X,Y,Z,v) form. As there are only a few discrete values, then

contourf(B0,B1,Z,unique(Z(:));

Answer 3

[even coil]

Sorry, I should have included a MWE. The code is below. I attach the necessary data files for my example. Also, the plots are below.

 clear;
 close all;

 B0 = load('B0.txt');
 B1 = load('B1.txt');
 fontsize = 20;
 colormap(gray);

 Z = load('Z.txt');
 Z = round(Z*1000)/1000;
 Z(abs(Z) == Inf) = 1;

 % This creates many lines
 contourf(B0, B1, Z);
 caxis([-.5 1]);
 xlim([-.2 1.6]);
 ylim([-1 1]);
 print('-dpng', 'Version1.png');

 % Still wrong---there should be no light grey outline on the dark grey area
 % (Look at Z---it goes immediately from the smallest value -.1420 to the  largest
 % value of 1, without going through the intermediate value 0. MATLAB is
 % interpolating here.)
 close;
 colormap(gray);
 contourf(B0, B1, Z, unique(Z));
 caxis([-.5 1]);
 xlim([-.2 1.6]);
 ylim([-1 1]);
 print('-dpng', 'Version2.png');