Modify matrix for partial plot

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jojo
jojo 2020-5-9
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)
  5 个评论
显示 3更早的评论
Walter Roberson
Walter Roberson 2020-5-9
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
Walter Roberson 2020-5-9
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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darova
darova 2020-5-9
编辑：darova 2020-5-9
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
  2 个评论
jojo
jojo 2020-5-9
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'

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