slarf.c

来自「NIST Handwriting OCR Testbed」· C语言 代码 · 共 138 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 slarf_(char *side, integer *m, integer *n, real *v, 
	integer *incv, real *tau, real *c, integer *ldc, real *work)
{
/*  -- LAPACK auxiliary 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   
    =======   

    SLARF applies a real elementary reflector H to a real m by n matrix   
    C, from either the left or the right. H is represented in the form   

          H = I - tau * v * v'   

    where tau is a real scalar and v is a real vector.   

    If tau = 0, then H is taken to be the unit matrix.   

    Arguments   
    =========   

    SIDE    (input) CHARACTER*1   
            = 'L': form  H * C   
            = 'R': form  C * H   

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

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

    V       (input) REAL array, dimension   
                       (1 + (M-1)*abs(INCV)) if SIDE = 'L'   
                    or (1 + (N-1)*abs(INCV)) if SIDE = 'R'   
            The vector v in the representation of H. V is not used if   
            TAU = 0.   

    INCV    (input) INTEGER   
            The increment between elements of v. INCV <> 0.   

    TAU     (input) REAL   
            The value tau in the representation of H.   

    C       (input/output) REAL array, dimension (LDC,N)   
            On entry, the m by n matrix C.   
            On exit, C is overwritten by the matrix H * C if SIDE = 'L', 
  
            or C * H if SIDE = 'R'.   

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

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

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


    
   Parameter adjustments   
       Function Body */
    /* Table of constant values */
    static real c_b4 = 1.f;
    static real c_b5 = 0.f;
    static integer c__1 = 1;
    
    /* System generated locals */
    integer c_dim1, c_offset;
    real r__1;
    /* Local variables */
    extern /* Subroutine */ int sger_(integer *, integer *, real *, real *, 
	    integer *, real *, integer *, real *, integer *);
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int sgemv_(char *, integer *, integer *, real *, 
	    real *, integer *, real *, integer *, real *, real *, integer *);



#define V(I) v[(I)-1]
#define WORK(I) work[(I)-1]

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

    if (lsame_(side, "L")) {

/*        Form  H * C */

	if (*tau != 0.f) {

/*           w := C' * v */

	    sgemv_("Transpose", m, n, &c_b4, &C(1,1), ldc, &V(1), incv, &
		    c_b5, &WORK(1), &c__1);

/*           C := C - v * w' */

	    r__1 = -(doublereal)(*tau);
	    sger_(m, n, &r__1, &V(1), incv, &WORK(1), &c__1, &C(1,1), 
		    ldc);
	}
    } else {

/*        Form  C * H */

	if (*tau != 0.f) {

/*           w := C * v */

	    sgemv_("No transpose", m, n, &c_b4, &C(1,1), ldc, &V(1), 
		    incv, &c_b5, &WORK(1), &c__1);

/*           C := C - w * v' */

	    r__1 = -(doublereal)(*tau);
	    sger_(m, n, &r__1, &WORK(1), &c__1, &V(1), incv, &C(1,1), 
		    ldc);
	}
    }
    return 0;

/*     End of SLARF */

} /* slarf_ */