Question on implementing Jacobi Method

2 次查看（过去 30 天）
Zhukun Wang
Zhukun Wang 2021-3-16
回答： Alan Stevens 2021-3-16
function [x,info,relres] = myJacobi(A,b,MaxIter,TOL)
%Jacobi Method
A=zeros(n,n);
%x0=zeros(n,1);
x=zeros(n,1);
b=zeros(n,1);
MaxIter=10*n;
TOL=1.e-4;
k=1;
while k<=MaxIter
for i=1:n
x(i)=(b(i)-a(i,[1:i-1,i+1:n])*x([1:i-1,i+1:n]))/a(i,i);
if norm(A*x-b)/norm(b)<=TOL %abs(x-x0)<TOL
print(x);
end
end
k=k+1;
for i=1:n
%x0(i)=x(i);
print(x(i));
end
end
end
%This is demo codes I am trying to call the Jacobi function that I defined at the very beginning to solve for another system.
N=50;
A=gallery('poisson',N);
n=size(A,1);
xs=ones(n,1);
b=A*xs(:);
MaxIter=10*n;
TOL=1.e-4;
t=cputime;
[x,info,relres]=myJacobi(A,b,MaxIter,TOL); % Jacobi example
mycput = cputime - t;
relerr = norm(xs-x)/norm(xs);
fprintf('size(A,1)=%d,info=%d, relres=%8.5e, relerr=%8.5e\n',...
n, info, relres, relerr);
fprintf('time =%8.5e\n', mycput);
The above is my code. What I am doing is divided into two parts. In the first part, I am inplementing Jacobi method into Matlab. In the second part which is outside of the function that I defined, I am trying to calculate another system by calling the function myJacobi. However, I do not know why matlab keeps saying the line with N=50 is not right. Can somebody help me figure it out? What are things I might need to change? Thanks a lot.

请先登录，再回答此问题。

回答（1 个）

Alan Stevens
Alan Stevens 2021-3-16
More like this perhaps
N=10; % 50;
A=gallery('poisson',N);
n=size(A,1);
xs=ones(n,1);
b=A*xs(:);
MaxIter=10*n;
TOL=1.e-4;
t=cputime;
[x]=myJacobi(A,b,MaxIter,TOL,n); % Jacobi example
mycput = cputime - t;
relerr = norm(xs-x)/norm(xs);
fprintf('size(A,1) = %d, relerr = %8.5e\n',n, relerr);
fprintf('time = %8.5e\n', mycput);
function [x] = myJacobi(A,b,MaxIter,TOL,n)
%Jacobi Method
x=zeros(n,1);
k=1;
err = 1;
while k<=MaxIter && err>TOL
for i=1:n
x(i)=(b(i)-A(i,[1:i-1,i+1:n])*x([1:i-1,i+1:n]))/A(i,i);
end
err = norm(A*x-b)/norm(b);
k=k+1;
end
disp(k)
end
Note: you hadn't implemented any calculation for info and relres, so they've been removed in the version here.

类别

在 Help Center 和 File Exchange 中查找有关 Software Development Tools 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by