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83 lines
1.7 KiB
83 lines
1.7 KiB
15 years ago
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#include "clapack.h"
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doublereal dnrm2_(integer *n, doublereal *x, integer *incx)
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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 ret_val, d__1;
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/* Builtin functions */
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double sqrt(doublereal);
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/* Local variables */
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integer ix;
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doublereal ssq, norm, scale, absxi;
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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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/* DNRM2 returns the euclidean norm of a vector via the function */
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/* name, so that */
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/* DNRM2 := sqrt( x'*x ) */
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/* -- This version written on 25-October-1982. */
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/* Modified on 14-October-1993 to inline the call to DLASSQ. */
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/* Sven Hammarling, Nag Ltd. */
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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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/* Parameter adjustments */
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--x;
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/* Function Body */
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if (*n < 1 || *incx < 1) {
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norm = 0.;
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} else if (*n == 1) {
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norm = abs(x[1]);
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} else {
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scale = 0.;
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ssq = 1.;
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/* The following loop is equivalent to this call to the LAPACK */
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/* auxiliary routine: */
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/* CALL DLASSQ( N, X, INCX, SCALE, SSQ ) */
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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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ssq = ssq * (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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ssq += 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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norm = scale * sqrt(ssq);
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}
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ret_val = norm;
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return ret_val;
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/* End of DNRM2. */
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} /* dnrm2_ */
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