slassq.c

来自「NIST Handwriting OCR Testbed」· C语言 代码 · 共 105 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 slassq_(integer *n, real *x, integer *incx, real *scale, 
	real *sumsq)
{
/*  -- LAPACK auxiliary routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       October 31, 1992   


    Purpose   
    =======   

    SLASSQ  returns the values  scl  and  smsq  such that   

       ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq, 
  

    where  x( i ) = X( 1 + ( i - 1 )*INCX ). The value of  sumsq  is   
    assumed to be non-negative and  scl  returns the value   

       scl = max( scale, abs( x( i ) ) ).   

    scale and sumsq must be supplied in SCALE and SUMSQ and   
    scl and smsq are overwritten on SCALE and SUMSQ respectively.   

    The routine makes only one pass through the vector x.   

    Arguments   
    =========   

    N       (input) INTEGER   
            The number of elements to be used from the vector X.   

    X       (input) REAL   
            The vector for which a scaled sum of squares is computed.   
               x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.   

    INCX    (input) INTEGER   
            The increment between successive values of the vector X.   
            INCX > 0.   

    SCALE   (input/output) REAL   
            On entry, the value  scale  in the equation above.   
            On exit, SCALE is overwritten with  scl , the scaling factor 
  
            for the sum of squares.   

    SUMSQ   (input/output) REAL   
            On entry, the value  sumsq  in the equation above.   
            On exit, SUMSQ is overwritten with  smsq , the basic sum of   
            squares from which  scl  has been factored out.   

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


    
   Parameter adjustments   
       Function Body */
    /* System generated locals */
    integer i__1, i__2;
    real r__1;
    /* Local variables */
    static real absxi;
    static integer ix;


#define X(I) x[(I)-1]


    if (*n > 0) {
	i__1 = (*n - 1) * *incx + 1;
	i__2 = *incx;
	for (ix = 1; *incx < 0 ? ix >= (*n-1)**incx+1 : ix <= (*n-1)**incx+1; ix += *incx) {
	    if (X(ix) != 0.f) {
		absxi = (r__1 = X(ix), dabs(r__1));
		if (*scale < absxi) {
/* Computing 2nd power */
		    r__1 = *scale / absxi;
		    *sumsq = *sumsq * (r__1 * r__1) + 1;
		    *scale = absxi;
		} else {
/* Computing 2nd power */
		    r__1 = absxi / *scale;
		    *sumsq += r__1 * r__1;
		}
	    }
/* L10: */
	}
    }
    return 0;

/*     End of SLASSQ */

} /* slassq_ */