Modify matrix for partial plot

Question

jojo 2020-5-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/524151-modify-matrix-for-partial-plot

评论： Walter Roberson 2020-5-9

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)  

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Walter Roberson 2020-5-9

在 MATLAB Online 中打开

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 2020-5-9

在 MATLAB Online 中打开

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)

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Answer 1

darova 2020-5-9

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/524151-modify-matrix-for-partial-plot#answer_431389

编辑：darova 2020-5-9

在 MATLAB Online 中打开

Untitled.m

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)