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82 lines
1.7 KiB
82 lines
1.7 KiB
#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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