How to get a specific shape of a contour plot in MATLAB

I have plotted this figure using the MATLAB contourf(x,y,z) function, where x and y are the vectors and Z is a matrix. How can only I get the Lower triangle?

Thank You.

x = linspace(0,1,11);
y = linspace(0,1,11);
Z = [0         0         0         0         0         0         0         0         0         0         0
         0   -2.5688   -3.8969   -1.6041    2.3402    6.1319    7.8457    4.7247    0.3582         0         0
         0   -4.6769   -8.1296   -4.7086    3.0256    9.9652   12.6373    7.2991         0         0         0
         0   -6.0168  -10.9420   -8.0819    0.2356    7.1892    7.7445         0         0         0         0
         0   -7.1333  -12.4002   -9.9456   -2.8682    2.7014         0         0         0         0         0
         0   -7.6917  -11.9661   -8.3691   -2.2996         0         0         0         0         0         0
         0   -6.8522   -9.0808   -4.4436         0         0         0         0         0         0         0
         0   -4.3650   -4.4620         0         0         0         0         0         0         0         0
         0   -1.4376         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0];
newpoints = 100;
[xq,yq] = meshgrid(...
            linspace(min(min(x,[],2)),max(max(x,[],2)),newpoints ),...
            linspace(min(min(y,[],1)),max(max(y,[],1)),newpoints )...
          );
Bumatrixq = interp2(x,y,Z',xq,yq,'cubic');

figure(1)
[~,~]=contourf(xq,yq,Bumatrixq,10,'Linestyle',':','Linewidth',0.01);
xlabel('$x$','FontSize',20,'interpreter','latex')
ylabel('$y$','FontSize',20,'interpreter','latex')

[Sam Chak]

@Bibigul, Can you show the code for the generating the same contour in the image?

Do you mean to plot a straight black line between (0, 1) and (1, 0)?

plot([0 1], [1 0], 'k', LineWidth=3)

[Bibigul]

@Sam Chak No I want the lower triangle part of the plot.

[Dyuman Joshi]

As requested before, please share the code used for generating the contour plot shown in the image.

[Sam Chak]

@Bibigul, Do you mean to display the Lower Triangle protion with a white shade by covering the Upper Triangle?

[Bibigul]

@Sam Chak Yes

[Bibigul]

@Dyuman Joshi the code has been added.

Answer 1

[Sam Chak]

Hi @Bibigul,

Check if this is what you want.

x = linspace(0,1,11);
y = linspace(0,1,11);
Z = [0         0         0         0         0         0         0         0         0         0         0
         0   -2.5688   -3.8969   -1.6041    2.3402    6.1319    7.8457    4.7247    0.3582         0         0
         0   -4.6769   -8.1296   -4.7086    3.0256    9.9652   12.6373    7.2991         0         0         0
         0   -6.0168  -10.9420   -8.0819    0.2356    7.1892    7.7445         0         0         0         0
         0   -7.1333  -12.4002   -9.9456   -2.8682    2.7014         0         0         0         0         0
         0   -7.6917  -11.9661   -8.3691   -2.2996         0         0         0         0         0         0
         0   -6.8522   -9.0808   -4.4436         0         0         0         0         0         0         0
         0   -4.3650   -4.4620         0         0         0         0         0         0         0         0
         0   -1.4376         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0];
newpoints = 100;
[xq,yq] = meshgrid(...
            linspace(min(min(x,[],2)),max(max(x,[],2)),newpoints ),...
            linspace(min(min(y,[],1)),max(max(y,[],1)),newpoints )...
          );
Bumatrixq = interp2(x,y,Z',xq,yq,'cubic');
contourf(xq, yq, Bumatrixq, 8), hold on
xlabel('x'), ylabel('y')
xx = [0 1 1];
yy = [1 0 1];
patch(xx, yy, 'white')

[Bibigul]

@Sam Chak it is exactly what I wanted. Thank you very much for the help.

Answer 2

[Dyuman Joshi]

One simple way to obtain that is to fill the upper half with white color -

x = linspace(0,1,11);
y = linspace(0,1,11);
Z = [0         0         0         0         0         0         0         0         0         0         0
         0   -2.5688   -3.8969   -1.6041    2.3402    6.1319    7.8457    4.7247    0.3582         0         0
         0   -4.6769   -8.1296   -4.7086    3.0256    9.9652   12.6373    7.2991         0         0         0
         0   -6.0168  -10.9420   -8.0819    0.2356    7.1892    7.7445         0         0         0         0
         0   -7.1333  -12.4002   -9.9456   -2.8682    2.7014         0         0         0         0         0
         0   -7.6917  -11.9661   -8.3691   -2.2996         0         0         0         0         0         0
         0   -6.8522   -9.0808   -4.4436         0         0         0         0         0         0         0
         0   -4.3650   -4.4620         0         0         0         0         0         0         0         0
         0   -1.4376         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0
         0         0         0         0         0         0         0         0         0         0         0];
newpoints = 100;
[xq,yq] = meshgrid(linspace(min(min(x,[],2)),max(max(x,[],2)),newpoints ),...
            linspace(min(min(y,[],1)),max(max(y,[],1)),newpoints ));
Bumatrixq = interp2(x,y,Z',xq,yq,'cubic');

figure(1)
hold on
contourf(xq,yq,Bumatrixq,10,'Linestyle',':','Linewidth',0.01)
xlabel('$x$','FontSize',20,'interpreter','latex')
ylabel('$y$','FontSize',20,'interpreter','latex')

%Add border for the region
plot([0 1 0 0],[1 0 0 1],'k-','LineWidth',2)
%Fill the upper region with white color
fill([0 1 1],[1 0 1],'w')

[Bibigul]

@Dyuman Joshi thank you very much for the help.

[Sam Chak]

Hi @Bibigul, the 'fill()' function also works, and the @Dyuman Joshi's solution deserves a vote.

[Bibigul]

Yes @Sam Chak I appriciate @Dyuman Joshi's effort too. I have voted both solutions. Thank you both for your help.