tasks a-s

Task/Polynomial-regression/C/polynomial-regression-1.c

@@ -0,0 +1,8 @@
+#ifndef _POLIFITGSL_H
+#define _POLIFITGSL_H
+#include <gsl/gsl_multifit.h>
+#include <stdbool.h>
+#include <math.h>
+bool polynomialfit(int obs, int degree,
+		   double *dx, double *dy, double *store); /* n, p */
+#endif

Task/Polynomial-regression/C/polynomial-regression-2.c

@@ -0,0 +1,42 @@
+#include "polifitgsl.h"
+
+bool polynomialfit(int obs, int degree,
+		   double *dx, double *dy, double *store) /* n, p */
+{
+  gsl_multifit_linear_workspace *ws;
+  gsl_matrix *cov, *X;
+  gsl_vector *y, *c;
+  double chisq;
+
+  int i, j;
+
+  X = gsl_matrix_alloc(obs, degree);
+  y = gsl_vector_alloc(obs);
+  c = gsl_vector_alloc(degree);
+  cov = gsl_matrix_alloc(degree, degree);
+
+  for(i=0; i < obs; i++) {
+    gsl_matrix_set(X, i, 0, 1.0);
+    for(j=0; j < degree; j++) {
+      gsl_matrix_set(X, i, j, pow(dx[i], j));
+    }
+    gsl_vector_set(y, i, dy[i]);
+  }
+
+  ws = gsl_multifit_linear_alloc(obs, degree);
+  gsl_multifit_linear(X, y, c, cov, &chisq, ws);
+
+  /* store result ... */
+  for(i=0; i < degree; i++)
+  {
+    store[i] = gsl_vector_get(c, i);
+  }
+
+  gsl_multifit_linear_free(ws);
+  gsl_matrix_free(X);
+  gsl_matrix_free(cov);
+  gsl_vector_free(y);
+  gsl_vector_free(c);
+  return true; /* we do not "analyse" the result (cov matrix mainly)
+		  to know if the fit is "good" */
+}

Task/Polynomial-regression/C/polynomial-regression-3.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+#include "polifitgsl.h"
+
+#define NP 11
+double x[] = {0,  1,  2,  3,  4,  5,  6,   7,   8,   9,   10};
+double y[] = {1,  6,  17, 34, 57, 86, 121, 162, 209, 262, 321};
+
+#define DEGREE 3
+double coeff[DEGREE];
+
+int main()
+{
+  int i;
+
+  polynomialfit(NP, DEGREE, x, y, coeff);
+  for(i=0; i < DEGREE; i++) {
+    printf("%lf\n", coeff[i]);
+  }
+  return 0;
+}