1 files changed, 46 insertions, 0 deletions
diff --git a/gsl-1.9/linalg/givens.c b/gsl-1.9/linalg/givens.c
new file mode 100644
index 0000000..c3875d6
--- /dev/null
+++ b/gsl-1.9/linalg/givens.c
@@ -0,0 +1,46 @@
+/* linalg/givens.c
+ * 
+ * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman, Brian Gough
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/* Generate a Givens rotation (cos,sin) which takes v=(x,y) to (|v|,0) 
+
+   From Golub and Van Loan, "Matrix Computations", Section 5.1.8 */
+
+inline static void
+create_givens (const double a, const double b, double *c, double *s)
+{
+  if (b == 0)
+    {
+      *c = 1;
+      *s = 0;
+    }
+  else if (fabs (b) > fabs (a))
+    {
+      double t = -a / b;
+      double s1 = 1.0 / sqrt (1 + t * t);
+      *s = s1;
+      *c = s1 * t;
+    }
+  else
+    {
+      double t = -b / a;
+      double c1 = 1.0 / sqrt (1 + t * t);
+      *c = c1;
+      *s = c1 * t;
+    }
+}