1function Y = cod_qmult (Q, X, method)
2%COD_QMULT computes Q'*X, Q*X, X*Q', or X*Q with Q from COD_SPARSE.
3% Q is a matrix or a struct representing the SPQR Householder form.  An
4% additional column permutation matrix Q.Pc may be present in the Q struct.
5%
6% Usage: Y = cod_qmult (Q,X,method)
7%
8%   method = 0: Y = Q'*X    default if 3rd input argument is not present.
9%   method = 1: Y = Q*X
10%   method = 2: Y = X*Q'
11%   method = 3: Y = X*Q
12%
13% Example:
14%
15%   [U, R, V, r] = cod_sparse (A) ;
16%   Y = cod_qmult (U, X, 0) ;                   % Y = U' * X
17%   U = cod_qmult (U, speye (size (U.H,1)), 1)  % convert U to matrix form
18%
19% See also cod_sparse, spqr, spqr_qmult
20
21% Copyright 2011-2012, Timothy A. Davis, http://www.suitesparse.com
22
23if (nargin < 3)
24    method = 0 ;
25end
26
27% multiply Q and X
28if (isstruct (Q))
29    if (~isfield (Q, 'Pc'))
30        Y = spqr_qmult (Q, X, method) ;
31    else
32        switch method
33            case 0, Y = Q.Pc' * spqr_qmult (Q, X, method) ;
34            case 1, Y = spqr_qmult (Q, Q.Pc * X, method) ;
35            case 2, Y = spqr_qmult (Q, X * Q.Pc', method) ;
36            case 3, Y = spqr_qmult (Q, X, method) * Q.Pc ;
37        end
38    end
39else
40    switch method
41        case 0, Y = Q'*X ;
42        case 1, Y = Q*X ;
43        case 2, Y = X*Q' ;
44        case 3, Y = X*Q ;
45    end
46end
47