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104 lines
2.8 KiB
C
104 lines
2.8 KiB
C
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#include "clapack.h"
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/* Subroutine */ int dlassq_(integer *n, doublereal *x, integer *incx,
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doublereal *scale, doublereal *sumsq)
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{
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/* System generated locals */
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integer i__1, i__2;
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doublereal d__1;
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/* Local variables */
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integer ix;
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doublereal absxi;
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/* -- LAPACK auxiliary routine (version 3.1) -- */
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/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
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/* November 2006 */
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/* .. Scalar Arguments .. */
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/* .. */
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/* .. Array Arguments .. */
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/* .. */
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/* Purpose */
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/* ======= */
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/* DLASSQ returns the values scl and smsq such that */
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/* ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq, */
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/* where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is */
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/* assumed to be non-negative and scl returns the value */
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/* scl = max( scale, abs( x( i ) ) ). */
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/* scale and sumsq must be supplied in SCALE and SUMSQ and */
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/* scl and smsq are overwritten on SCALE and SUMSQ respectively. */
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/* The routine makes only one pass through the vector x. */
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/* Arguments */
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/* ========= */
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/* N (input) INTEGER */
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/* The number of elements to be used from the vector X. */
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/* X (input) DOUBLE PRECISION array, dimension (N) */
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/* The vector for which a scaled sum of squares is computed. */
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/* x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n. */
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/* INCX (input) INTEGER */
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/* The increment between successive values of the vector X. */
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/* INCX > 0. */
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/* SCALE (input/output) DOUBLE PRECISION */
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/* On entry, the value scale in the equation above. */
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/* On exit, SCALE is overwritten with scl , the scaling factor */
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/* for the sum of squares. */
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/* SUMSQ (input/output) DOUBLE PRECISION */
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/* On entry, the value sumsq in the equation above. */
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/* On exit, SUMSQ is overwritten with smsq , the basic sum of */
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/* squares from which scl has been factored out. */
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/* ===================================================================== */
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/* .. Parameters .. */
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/* .. */
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/* .. Local Scalars .. */
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/* .. */
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/* .. Intrinsic Functions .. */
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/* .. */
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/* .. Executable Statements .. */
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/* Parameter adjustments */
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--x;
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/* Function Body */
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if (*n > 0) {
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i__1 = (*n - 1) * *incx + 1;
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i__2 = *incx;
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for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
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if (x[ix] != 0.) {
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absxi = (d__1 = x[ix], abs(d__1));
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if (*scale < absxi) {
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/* Computing 2nd power */
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d__1 = *scale / absxi;
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*sumsq = *sumsq * (d__1 * d__1) + 1;
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*scale = absxi;
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} else {
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/* Computing 2nd power */
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d__1 = absxi / *scale;
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*sumsq += d__1 * d__1;
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}
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}
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/* L10: */
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}
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}
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return 0;
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/* End of DLASSQ */
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} /* dlassq_ */
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