dlassq.c

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/* dlassq.f -- translated by f2c (version 19941215).
   You must link the resulting object file with the libraries:
        -lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Subroutine */ int dlassq_(n, x, incx, scale, sumsq)
integer *n;
doublereal *x;
integer *incx;
doublereal *scale, *sumsq;
{
    /* System generated locals */
    integer i__1, i__2;
    doublereal d__1;

    /* Local variables */
    static doublereal absxi;
    static integer ix;


/*  -- LAPACK auxiliary routine (version 1.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/*     Courant Institute, Argonne National Lab, and Rice University */
/*     October 31, 1992 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DLASSQ  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) DOUBLE PRECISION */
/*          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) DOUBLE PRECISION */
/*          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) DOUBLE PRECISION */
/*          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. */

/* ===================================================================== 
*/

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

    /* Parameter adjustments */
    --x;

    /* Function Body */
    if (*n > 0) {
        i__1 = (*n - 1) * *incx + 1;
        i__2 = *incx;
        for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
            if (x[ix] != 0.) {
                absxi = (d__1 = x[ix], abs(d__1));
                if (*scale < absxi) {
/* Computing 2nd power */
                    d__1 = *scale / absxi;
                    *sumsq = *sumsq * (d__1 * d__1) + 1;
                    *scale = absxi;
                } else {
/* Computing 2nd power */
                    d__1 = absxi / *scale;
                    *sumsq += d__1 * d__1;
                }
            }
/* L10: */
        }
    }
    return 0;

/*     End of DLASSQ */

} /* dlassq_ */

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