sorg2r.c

来自「NIST Handwriting OCR Testbed」· C语言 代码 · 共 161 行

/*
* ======================================================================
* NIST Guide to Available Math Software.
* Fullsource for module SSYEVX.C from package CLAPACK.
* Retrieved from NETLIB on Fri Mar 10 14:23:44 2000.
* ======================================================================
*/
#include <f2c.h>

/* Subroutine */ int sorg2r_(integer *m, integer *n, integer *k, real *a, 
	integer *lda, real *tau, real *work, integer *info)
{
/*  -- LAPACK routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       February 29, 1992   


    Purpose   
    =======   

    SORG2R generates an m by n real matrix Q with orthonormal columns,   
    which is defined as the first n columns of a product of k elementary 
  
    reflectors of order m   

          Q  =  H(1) H(2) . . . H(k)   

    as returned by SGEQRF.   

    Arguments   
    =========   

    M       (input) INTEGER   
            The number of rows of the matrix Q. M >= 0.   

    N       (input) INTEGER   
            The number of columns of the matrix Q. M >= N >= 0.   

    K       (input) INTEGER   
            The number of elementary reflectors whose product defines the 
  
            matrix Q. N >= K >= 0.   

    A       (input/output) REAL array, dimension (LDA,N)   
            On entry, the i-th column must contain the vector which   
            defines the elementary reflector H(i), for i = 1,2,...,k, as 
  
            returned by SGEQRF in the first k columns of its array   
            argument A.   
            On exit, the m-by-n matrix Q.   

    LDA     (input) INTEGER   
            The first dimension of the array A. LDA >= max(1,M).   

    TAU     (input) REAL array, dimension (K)   
            TAU(i) must contain the scalar factor of the elementary   
            reflector H(i), as returned by SGEQRF.   

    WORK    (workspace) REAL array, dimension (N)   

    INFO    (output) INTEGER   
            = 0: successful exit   
            < 0: if INFO = -i, the i-th argument has an illegal value   

    ===================================================================== 
  


       Test the input arguments   

    
   Parameter adjustments   
       Function Body */
    /* Table of constant values */
    static integer c__1 = 1;
    
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;
    real r__1;
    /* Local variables */
    static integer i, j, l;
    extern /* Subroutine */ int sscal_(integer *, real *, real *, integer *), 
	    slarf_(char *, integer *, integer *, real *, integer *, real *, 
	    real *, integer *, real *), xerbla_(char *, integer *);



#define TAU(I) tau[(I)-1]
#define WORK(I) work[(I)-1]

#define A(I,J) a[(I)-1 + ((J)-1)* ( *lda)]

    *info = 0;
    if (*m < 0) {
	*info = -1;
    } else if (*n < 0 || *n > *m) {
	*info = -2;
    } else if (*k < 0 || *k > *n) {
	*info = -3;
    } else if (*lda < max(1,*m)) {
	*info = -5;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("SORG2R", &i__1);
	return 0;
    }

/*     Quick return if possible */

    if (*n <= 0) {
	return 0;
    }

/*     Initialise columns k+1:n to columns of the unit matrix */

    i__1 = *n;
    for (j = *k + 1; j <= *n; ++j) {
	i__2 = *m;
	for (l = 1; l <= *m; ++l) {
	    A(l,j) = 0.f;
/* L10: */
	}
	A(j,j) = 1.f;
/* L20: */
    }

    for (i = *k; i >= 1; --i) {

/*        Apply H(i) to A(i:m,i:n) from the left */

	if (i < *n) {
	    A(i,i) = 1.f;
	    i__1 = *m - i + 1;
	    i__2 = *n - i;
	    slarf_("Left", &i__1, &i__2, &A(i,i), &c__1, &TAU(i), &
		    A(i,i+1), lda, &WORK(1));
	}
	if (i < *m) {
	    i__1 = *m - i;
	    r__1 = -(doublereal)TAU(i);
	    sscal_(&i__1, &r__1, &A(i+1,i), &c__1);
	}
	A(i,i) = 1.f - TAU(i);

/*        Set A(1:i-1,i) to zero */

	i__1 = i - 1;
	for (l = 1; l <= i-1; ++l) {
	    A(l,i) = 0.f;
/* L30: */
	}
/* L40: */
    }
    return 0;

/*     End of SORG2R */

} /* sorg2r_ */