[Matlab-Based eBook]Introduction to Linear Algebra, Fourth Edition

我有这书， 可是， 传不上来，说是论坛有。给你个链接， 自己下载巴：

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http://vdisk.weibo.com/s/z8eg6HdRffcOA

1. function [E, R] = elim(A)
   
2. 
   
3. % elim  E*A = R factorization.
   
4. %
   
5. % E = elim(A) returns the elimination matrix E
   
6. % that gives the reduced row echelon form E*A = R.
   
7. % If A is square and invertible, then E = inv(A).
   
8. %
   
9. % [E, R] = elim(A) returns the elimination matrix E
   
10. % and the reduced row echelon form R.
    
11. %
    
12. % See also lu, slu, splu, plu.
    
13. 
    
14. [m, n] = size(A);
    
15. I = eye(m);
    
16. %
    
17. % Elimination on the augmented matrix [A I] yields [R E].
    
18. %
    
19. RE = rref([A I]);
    
20. R = RE(:, 1:n);
    
21. E = RE(:, (n+1):(m+n));

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1. function [k, p] = findpiv(A, k, p, tol)
   
2. 
   
3. % findpiv  Used by plu to find a pivot for Gaussian elimination.
   
4. %
   
5. % [r, p] = findpiv(A(k:m, p:n), k, p, tol) finds the first element in
   
6. % the specified submatrix which is larger than tol in absolute value.
   
7. % It returns indices r and p so that A(r, p) is the pivot.
   
8. 
   
9. [m,  n] = size(A);
   
10. r = find(abs(A(:)) > tol);
    
11. if isempty(r), return, end
    
12. %
    
13. r = r(1);
    
14. j = fix((r-1)/m)+1;
    
15. p = p+j-1;
    
16. k = k+r-(j-1)*m-1;

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thanks useful