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Em không biết đoạn code này sai chỗ nào mà cứ báo P undefine. Thật sự thì cái này cũng copy từ trên mạng về thôi nên ko hiểu
Code:
function [P,dP,Z] = jacobi(A,B,P,delta,max1)
%---------------------------------------------------------------------------
%JACOBI Jacobi iteration for solving a linear system.
% Sample call
% [X,dX] = jacobi(A,B,P,delta,max1)
% [X,dX,Z] = jacobi(A,B,P,delta,max1)
% Inputs
% A coefficient matrix
% B right hand side vector
% P starting vector
% delta convergence tolerance
% max1 maximum number of iterations
% Return
% X solution vector
% dX error estimate vector
% Z History matrix of the iterations
%
% NUMERICAL METHODS: MATLAB Programs, (c) John H. Mathews 1995
% To accompany the text:
% NUMERICAL METHODS for Mathematics, Science and Engineering, 2nd Ed, 1992
% Prentice Hall, Englewood Cliffs, New Jersey, 07632, U.S.A.
% Prentice Hall, Inc.; USA, Canada, Mexico ISBN 0-13-624990-6
% Prentice Hall, International Editions: ISBN 0-13-625047-5
% This free software is compliments of the author.
% E-mail address: in%"mathews@fullerton.edu"
%
% Algorithm 3.4 (Jacobi Iteration).
% Section 3.7, Iterative Methods for Linear Systems, Page 186
%---------------------------------------------------------------------------
Z = P';
n = length(B);
Pnew = P;
for k=1:max1,
for r = 1:n,
Sum1 = B(r) - A(r,[1:r-1,r+1:n])*P([1:r-1,r+1:n]);
Pnew(r) = Sum1/A(r,r);
end
dP = abs(Pnew-P);
err = norm(dP);
relerr = err/(norm(Pnew)+eps);
P = Pnew;
Z = [Z;P'];
if (err<delta)|(relerr<delta), break, end
end
