/* nag_simple_linear_regression (g02cac) Example Program.
 *
 * Copyright 1992 Numerical Algorithms Group.
 *
 * Mark 3, 1992.
 * Mark 8 revised, 2004.
 */

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nagg02.h>

int main(void)
{
  Integer exit_status=0, i, n;
  NagError fail;
  Nag_SumSquare mean;
  char m, w;
  double a, b, df, err_a, err_b, rsq, rss, *wt=0, *wtptr, *x=0, *y=0;

  INIT_FAIL(fail);
  Vprintf("nag_simple_linear_regression (g02cac) Example Program Results\n");
  /* Skip heading in data file */
  Vscanf("%*[^\n]");
  Vscanf(" %c %c",&m, &w);
  Vscanf("%ld", &n);
  if (n >= (m == 'M' || m == 'm' ? 2 : 1))
    {
      if ( !( x = NAG_ALLOC(n, double)) ||
           !( y = NAG_ALLOC(n, double)) ||
           !( wt = NAG_ALLOC(n, double)) )
        {
          Vprintf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  else
    {
      Vprintf("Invalid n.\n");
      exit_status = 1;
      return exit_status;
    }
  if (m == 'M' || m == 'm')
    mean = Nag_AboutMean;
  else
    mean = Nag_AboutZero;
  if (w == 'W' || w == 'w')
    {
      wtptr = wt;
      for(i = 0; i < n; ++i)
        Vscanf("%lf%lf%lf", &x[i], &y[i], &wt[i]);
    }
  else
    {
      wtptr = (double *)0;
      for(i = 0; i < n; ++i)
        Vscanf("%lf%lf", &x[i], &y[i]);
    }

  /* nag_simple_linear_regression (g02cac).
   * Simple linear regression with or without a constant term,
   * data may be weighted
   */
  nag_simple_linear_regression(mean, n, x, y, wtptr, &a, &b, &err_a, &err_b,
                               &rsq, &rss, &df, &fail);
  if (fail.code != NE_NOERROR)
    {
      Vprintf("Error from nag_simple_linear_regression (g02cac).\n%s\n",
              fail.message);
      exit_status = 1;
      goto END;
    }


  if (mean == Nag_AboutMean)
    {
      Vprintf("\nRegression constant a = %6.4f\n\n", a);
      Vprintf("Standard error of the regression constant a = %6.4f\n\n",
              err_a);
    }

  Vprintf("Regression coefficient b = %6.4f\n\n", b);
  Vprintf("Standard error of the regression coefficient b = %6.4f\n\n",
          err_b);

  Vprintf("The regression coefficient of determination = %6.4f\n\n", rsq);
  Vprintf("The sum of squares of the residuals about the "
          "regression = %6.4f\n\n", rss);
  Vprintf("Number of degrees of freedom about the "
          "regression = %6.4f\n\n",df);
 END:
  if (x) NAG_FREE(x);
  if (y) NAG_FREE(y);
  if (wt) NAG_FREE(wt);
  return exit_status;
}