1 files changed, 101 insertions, 0 deletions
diff --git a/gsl-1.9/poly/dd.c b/gsl-1.9/poly/dd.c
new file mode 100644
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--- /dev/null
+++ b/gsl-1.9/poly/dd.c
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+/* interpolation/interp_poly.c
+ * 
+ * Copyright (C) 2001 DAN, HO-JIN
+ * 
+ * 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.
+ */
+
+/* Modified for standalone use in polynomial directory, B.Gough 2001 */
+
+#include <config.h>
+#include <gsl/gsl_errno.h>
+#include <gsl/gsl_poly.h>
+
+int
+gsl_poly_dd_init (double dd[], const double xa[], const double ya[],
+                  size_t size)
+{
+  size_t i, j;
+
+  /* Newton's divided differences */
+
+  dd[0] = ya[0];
+
+  for (j = size - 1; j >= 1; j--)
+    {
+      dd[j] = (ya[j] - ya[j - 1]) / (xa[j] - xa[j - 1]);
+    }
+
+  for (i = 2; i < size; i++)
+    {
+      for (j = size - 1; j >= i; j--)
+        {
+          dd[j] = (dd[j] - dd[j - 1]) / (xa[j] - xa[j - i]);
+        }
+    }
+
+  return GSL_SUCCESS;
+}
+
+#ifndef HIDE_INLINE_STATIC
+double
+gsl_poly_dd_eval (const double dd[], const double xa[], const size_t size, const double x)
+{
+  size_t i;
+  double y = dd[size - 1];
+
+  for (i = size - 1; i--;)
+    {
+      y = dd[i] + (x - xa[i]) * y;
+    }
+
+  return y;
+}
+#endif
+
+int
+gsl_poly_dd_taylor (double c[], double xp, 
+                    const double dd[], const double xa[], size_t size,
+                    double w[])
+{
+  size_t i, j;
+
+  for (i = 0; i < size; i++)
+    {
+      c[i] = 0.0;
+      w[i] = 0.0;
+    }
+
+  w[size - 1] = 1.0;
+
+  c[0] = dd[0];
+
+  for (i = size - 1; i > 0 && i--;)
+    {
+      w[i] = -w[i + 1] * (xa[size - 2 - i] - xp);
+
+      for (j = i + 1; j < size - 1; j++)
+        {
+          w[j] = w[j] - w[j + 1] * (xa[size - 2 - i] - xp);
+        }
+
+      for (j = i; j < size; j++)
+        {
+          c[j - i] += w[j] * dd[size - i - 1];
+        }
+    }
+
+  return GSL_SUCCESS;
+}