/*      driver for hybrj example. */

#include <stdio.h>
#include <math.h>
#include <assert.h>
#include <minpack.h>
#define real __minpack_real__

void fcn(const int *n, const real *x, real *fvec, real *fjac, const int *ldfjac, 
	 int *iflag);

int main()
{
#if (defined(__MINGW32__) && !defined(_UCRT)) || (defined(_MSC_VER) && (_MSC_VER < 1900))
  _set_output_format(_TWO_DIGIT_EXPONENT);
#endif
  int j, n, ldfjac, maxfev, mode, nprint, info, nfev, njev, lr;
  real xtol, factor, fnorm;
  real x[9], fvec[9], fjac[9*9], diag[9], r[45], qtf[9],
    wa1[9], wa2[9], wa3[9], wa4[9];
  int one=1;

  n = 9;

/*      the following starting values provide a rough solution. */

  for (j=1; j<=9; j++) {
    x[j-1] = -1.;
  }

  ldfjac = 9;
  lr = 45;

/*      set xtol to the square root of the machine precision. */
/*      unless high solutions are required, */
/*      this is the recommended setting. */

  xtol = sqrt(__minpack_func__(dpmpar)(&one));

  maxfev = 1000;
  mode = 2;
  for (j=1; j<=9; j++) {
    diag[j-1] = 1.;
  }
  factor = 1.e2;
  nprint = 0;

 __minpack_func__(hybrj)(&fcn, &n, x, fvec, fjac, &ldfjac, &xtol, &maxfev, diag, 
	&mode, &factor, &nprint, &info, &nfev, &njev, r, &lr, qtf, 
	wa1, wa2, wa3, wa4);
 fnorm = __minpack_func__(enorm)(&n, fvec);

 printf("     final l2 norm of the residuals%15.7g\n\n", (double)fnorm);
 printf("     number of function evaluations%10i\n\n", nfev);
 printf("     number of jacobian evaluations%10i\n\n", njev);
 printf("     exit parameter                %10i\n\n", info);
 printf("     final approximate solution\n\n");
 for (j=1; j<=n; j++) {
   printf("%s%15.7g", j%3==1?"\n     ":"", (double)x[j-1]);
 }
 printf("\n");
 return 0;
}

void fcn(const int *n, const real *x, real *fvec, real *fjac, const int *ldfjac, 
	 int *iflag)
{
  
  /*      subroutine fcn for hybrj example. */

  int j, k;
  real temp, temp1, temp2;
  assert(*n == 9);

  if (*iflag == 0) {
    /*      insert print statements here when nprint is positive. */
    /* if the nprint parameter to lmder is positive, the function is
       called every nprint iterations with iflag=0, so that the
       function may perform special operations, such as printing
       residuals. */
    return;
  }

  if (*iflag != 2) {
    /* compute residuals */
    for (k=1; k <= *n; k++) {
      temp = (3 - 2*x[k-1])*x[k-1];
      temp1 = 0;
      if (k != 1) {
        temp1 = x[k-1-1];
      }
      temp2 = 0;
      if (k != *n) {
        temp2 = x[k+1-1];
      }
      fvec[k-1] = temp - temp1 - 2*temp2 + 1;
    }
  } else {
    /* compute Jacobian */
    for (k = 1; k <= *n; k++) {
      for (j=1; j <= *n; j++) {
        fjac[k-1 + *ldfjac*(j-1)] = 0;
      }
      fjac[k-1 + *ldfjac*(k-1)] = 3 - 4*x[k-1];
      if (k != 1) {
        fjac[k-1 + *ldfjac*(k-1-1)] = -1;
      }
      if (k != *n) {
        fjac[k-1 + *ldfjac*(k+1-1)] = -2;
      }
    }      
  }
  return;
}

