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/* makerotation - Construct rotation from x to y by alpha. */
/* XLISP-STAT 2.1 Copyright (c) 1990, by Luke Tierney */
/* Additions to Xlisp 2.1, Copyright (c) 1989 by David Michael Betz */
/* You may give out copies of this software; for conditions see the */
/* file COPYING included with this distribution. */
#include "linalg.h"
VOID make_rotation P6C(int, n,
double *, rot,
double *, x,
double *, y,
int, use_alpha,
double, alpha)
{
double nx, ny, xy, c, s, cc, cm1, a, b;
int i, j, in;
for (i = 0, in = 0; i < n; i++, in += n) {
for (j = 0; j < n; j++)
rot[in + j] = 0.0;
rot[in + i] = 1.0;
}
nx = blas_dnrm2(n, x, 1);
ny = blas_dnrm2(n, y, 1);
if (nx == 0.0 || ny == 0.0) return;
blas_dscal(n, 1.0 / nx, x, 1);
blas_dscal(n, 1.0 / ny, y, 1);
xy = blas_ddot(n, x, 1, y, 1);
c = (use_alpha) ? cos(alpha) : xy;
cc = 1 - c * c;
s = (use_alpha) ? sin(alpha) : sqrt(cc > 0 ? cc : 0.0);
cm1 = c - 1.0;
blas_daxpy(n, -xy, x, 1, y, 1);
ny = blas_dnrm2(n, y, 1);
if (ny == 0.0)
return;
blas_dscal(n, 1.0 / ny, y, 1);
for (i = 0, in = 0; i < n; i++, in += n) {
a = x[i] * cm1 + y[i] * s;
b = - x[i] * s + y[i] * cm1;
for (j = 0; j < n; j++)
rot[in + j] = a * x[j] + b * y[j];
rot[in + i] += 1.0;
}
}
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