Modify matrix for partial plot

How can I modify the for loops to create a bracket-shaped domain? In otherwords, I would like to plot everything and omit the first quadrant. Thank you!

clear; close all; clc
n = 40;
x = linspace(0,8,n); dx = x(2)-x(1); y = x; dy = dx;
U = zeros(n);
U(n,1:n/2) =10;
U(n/2,n/2:n-1) =0;
U(1,1:n-1) = 10;
U(2:n,n/2) = 0;  
U(1:n/2,n) = 7;
U(n/2:n,n/2) = 0;

alpha=1;
ddt = 1/(4*(1/dx^2+1/dy^2));
for w=1:1000
    V = U;
    for i = 2:n/2-1
        for j = 2:n-1
            U(i,j) =ddt*((V(i+1,j)-2*V(i,j)+V(i-1,j))/dx^2+ (V(i,j+1)-V(i,j)+V(i,j-1))/dy^2)+ V(i,j);      
        end
    end

end
figure(1)
contour(y,x,U)
figure(2)
surf(y,x,U)  

[darova]

Calculate two regions separately

[Walter Roberson]

Uc = U;
Uc(1:end/2, 1:end/2) = nan;

figure(1);
contour(y, x, Uc);
figure(2)
surf(y, x, Uc, 'edgecolor', 'none')

[jojo]

I need to do this on the calculation part please. Not the plotting part. I tried doing 2 seperate for loop but I am unable to get blank region. Is this even possible to do without 'none' ?

[Walter Roberson]

 surf(y, x, Uc)

The 'edgecolor', 'none' just controls drawing the edges of each face. When you have many faces, the edges start to take over the visual impression, because the edges are constant width even when the faces get small.

[Walter Roberson]

x and y are both increasing, and you are using x for rows and y for columns. Which is the "first quadrant" ?

(x=0,y=0)    (x=0,y=4)    (x=0,y=8)


          A             B

(x=4,y=0)    (x=4,y=4)    (x=4,y=8)


          C            D

(x=8,y=0)   (x=8,y=4)    (x=8,y=8)

Answer 1

[darova]

Here are your bourndary conditions

n = 40;
x = linspace(0,8,n); dx = x(2)-x(1); y = x; dy = dx;
U = zeros(n);

U(n,1:n/2) =10;
U(n/2,n/2:n-1) =0+10;
U(1,1:n-1) = 10;
U(2:n,n/2) = 0+10;
U(1:n/2,n) = 7+3;
U(n/2:n,n/2) = 0+10;
alpha=1;
ddt = 1/(4*(1/dx^2+1/dy^2));
h = imagesc(U);
view(2)

Something is missing

I made some changes to your script. It still doesn't work

[jojo]

Thanks for the effort. I'm just trying to blank out a section of the plot using for loops (actual computation) instead of plotting using 'none'

[darova]

I did everything i can