sorm2l.c

来自「NIST Handwriting OCR Testbed」· C语言 代码 · 共 210 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 sorm2l_(char *side, char *trans, integer *m, integer *n, 
	integer *k, real *a, integer *lda, real *tau, real *c, integer *ldc, 
	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   
    =======   

    SORM2L overwrites the general real m by n matrix C with   

          Q * C  if SIDE = 'L' and TRANS = 'N', or   

          Q'* C  if SIDE = 'L' and TRANS = 'T', or   

          C * Q  if SIDE = 'R' and TRANS = 'N', or   

          C * Q' if SIDE = 'R' and TRANS = 'T',   

    where Q is a real orthogonal matrix defined as the product of k   
    elementary reflectors   

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

    as returned by SGEQLF. Q is of order m if SIDE = 'L' and of order n   
    if SIDE = 'R'.   

    Arguments   
    =========   

    SIDE    (input) CHARACTER*1   
            = 'L': apply Q or Q' from the Left   
            = 'R': apply Q or Q' from the Right   

    TRANS   (input) CHARACTER*1   
            = 'N': apply Q  (No transpose)   
            = 'T': apply Q' (Transpose)   

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

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

    K       (input) INTEGER   
            The number of elementary reflectors whose product defines   
            the matrix Q.   
            If SIDE = 'L', M >= K >= 0;   
            if SIDE = 'R', N >= K >= 0.   

    A       (input) REAL array, dimension (LDA,K)   
            The i-th column must contain the vector which defines the   
            elementary reflector H(i), for i = 1,2,...,k, as returned by 
  
            SGEQLF in the last k columns of its array argument A.   
            A is modified by the routine but restored on exit.   

    LDA     (input) INTEGER   
            The leading dimension of the array A.   
            If SIDE = 'L', LDA >= max(1,M);   
            if SIDE = 'R', LDA >= max(1,N).   

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

    C       (input/output) REAL array, dimension (LDC,N)   
            On entry, the m by n matrix C.   
            On exit, C is overwritten by Q*C or Q'*C or C*Q' or C*Q.   

    LDC     (input) INTEGER   
            The leading dimension of the array C. LDC >= max(1,M).   

    WORK    (workspace) REAL array, dimension   
                                     (N) if SIDE = 'L',   
                                     (M) if SIDE = 'R'   

    INFO    (output) INTEGER   
            = 0: successful exit   
            < 0: if INFO = -i, the i-th argument had 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, c_dim1, c_offset, i__1, i__2;
    /* Local variables */
    static logical left;
    static integer i;
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int slarf_(char *, integer *, integer *, real *, 
	    integer *, real *, real *, integer *, real *);
    static integer i1, i2, i3, mi, ni, nq;
    extern /* Subroutine */ int xerbla_(char *, integer *);
    static logical notran;
    static real aii;



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

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

    *info = 0;
    left = lsame_(side, "L");
    notran = lsame_(trans, "N");

/*     NQ is the order of Q */

    if (left) {
	nq = *m;
    } else {
	nq = *n;
    }
    if (! left && ! lsame_(side, "R")) {
	*info = -1;
    } else if (! notran && ! lsame_(trans, "T")) {
	*info = -2;
    } else if (*m < 0) {
	*info = -3;
    } else if (*n < 0) {
	*info = -4;
    } else if (*k < 0 || *k > nq) {
	*info = -5;
    } else if (*lda < max(1,nq)) {
	*info = -7;
    } else if (*ldc < max(1,*m)) {
	*info = -10;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("SORM2L", &i__1);
	return 0;
    }

/*     Quick return if possible */

    if (*m == 0 || *n == 0 || *k == 0) {
	return 0;
    }

    if (left && notran || ! left && ! notran) {
	i1 = 1;
	i2 = *k;
	i3 = 1;
    } else {
	i1 = *k;
	i2 = 1;
	i3 = -1;
    }

    if (left) {
	ni = *n;
    } else {
	mi = *m;
    }

    i__1 = i2;
    i__2 = i3;
    for (i = i1; i3 < 0 ? i >= i2 : i <= i2; i += i3) {
	if (left) {

/*           H(i) is applied to C(1:m-k+i,1:n) */

	    mi = *m - *k + i;
	} else {

/*           H(i) is applied to C(1:m,1:n-k+i) */

	    ni = *n - *k + i;
	}

/*        Apply H(i) */

	aii = A(nq-*k+i,i);
	A(nq-*k+i,i) = 1.f;
	slarf_(side, &mi, &ni, &A(1,i), &c__1, &TAU(i), &C(1,1), ldc, &WORK(1));
	A(nq-*k+i,i) = aii;
/* L10: */
    }
    return 0;

/*     End of SORM2L */

} /* sorm2l_ */