could you help me in this code

Question

nana 2023-5-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1957699-could-you-help-me-in-this-code

评论： Walter Roberson 2023-5-4

% Define grid parameters
h = 1/4;        % Grid spacing
x = -1:h:1;     % Grid points in x direction
y = -1:h:1;     % Grid points in y direction
n = length(x);  % Number of grid points
% Initialize solution matrix
U = zeros(n,n);
% Set boundary conditions
U(1,:) = 0;       % u(x,y)=0 along y=1
U(n,:) = 0;       % u(x,y)=0 along y=-1
U(:,1) = 0.5*U(:,2);     % u(x,y)=(1/2)u, x=-1,-1<y<1
U(:,n) = -0.5*U(:,n-1);  % u(x,y)=-(1/2)u, x=1,-1<y<1
% Construct matrix A
B = [-6 2 0 0 0; 1 -6 1 0 0; 0 1 -6 1 0; 0 0 1 -6 1; 0 0 0 2 -6.25];
I = eye(5);
A = kron(eye(n-2), B) + kron(diag(ones(n-3,1), -1), I) + kron(diag(ones(n-3,1), 1), I);
% Construct right-hand side vector rhs from boundary conditions
rhs = zeros(n^2, 1);
rhs(1:n) = U(1,:)' / h^2;
rhs(end-n+1:end) = -U(n,:)' / h^2;
rhs(1:n:n*(n-2)+1) = rhs(1:n:n*(n-2)+1) + U(:,1) / h^2;
rhs(n:n:n^2-n+1) = rhs(n:n:n^2-n+1) - U(:,n) / h^2;

Arrays have incompatible sizes for this operation.

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Answer 1

Walter Roberson 2023-5-4

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https://ww2.mathworks.cn/matlabcentral/answers/1957699-could-you-help-me-in-this-code#answer_1228799

在 MATLAB Online 中打开

You cannot add an 8 x 1 vector and a 9 x 1 vector.

% Define grid parameters
h = 1/4;        % Grid spacing
x = -1:h:1;     % Grid points in x direction
y = -1:h:1;     % Grid points in y direction
n = length(x);  % Number of grid points
% Initialize solution matrix
U = zeros(n,n);
% Set boundary conditions
U(1,:) = 0;       % u(x,y)=0 along y=1
U(n,:) = 0;       % u(x,y)=0 along y=-1
U(:,1) = 0.5*U(:,2);     % u(x,y)=(1/2)u, x=-1,-1<y<1
U(:,n) = -0.5*U(:,n-1);  % u(x,y)=-(1/2)u, x=1,-1<y<1
% Construct matrix A
B = [-6 2 0 0 0; 1 -6 1 0 0; 0 1 -6 1 0; 0 0 1 -6 1; 0 0 0 2 -6.25];
I = eye(5);
A = kron(eye(n-2), B) + kron(diag(ones(n-3,1), -1), I) + kron(diag(ones(n-3,1), 1), I);
% Construct right-hand side vector rhs from boundary conditions
rhs = zeros(n^2, 1);
rhs(1:n) = U(1,:)' / h^2;
rhs(end-n+1:end) = -U(n,:)' / h^2;
part1 = rhs(1:n:n*(n-2)+1);
part2 = U(:,1) / h^2;
size(part1)
ans = 1×2
     8     1
size(part2)
ans = 1×2
     9     1
rhs(1:n:n*(n-2)+1) = part1 + part2
Arrays have incompatible sizes for this operation.
rhs(n:n:n^2-n+1) = rhs(n:n:n^2-n+1) - U(:,n) / h^2;