/* Code to test the conjgrad minimiser */
/*
 * Copyright 1999, 2018 Graeme W. Gill
 * All rights reserved.
 *
 * This material is licenced under the GNU AFFERO GENERAL PUBLIC LICENSE Version 3 :-
 * see the License.txt file for licencing details.
 */

#include <stdio.h>
#include "numlib.h"

/*       Final approximate solution:                                       */

double expect[9] = {
	-0.5706545E+00,
	-0.6816283E+00,
	-0.7017325E+00,
	-0.7042129E+00,
	-0.7013690E+00,
	-0.6918656E+00,
	-0.6657920E+00,
	-0.5960342E+00,
	-0.4164121E+00 };

double fcn(		/* Return function value */
	void *fdata,	/* Opaque data pointer */
	double tp[]		/* Multivriate input value */
);

static double dfcn(
	void *fdata,
	double dp[],
	double tp[]
);

#define N 9

static void progress(void *pdata, int perc) {
	printf("%c% 3d%%",cr_char,perc); 
	if (perc == 100)
		printf("\n");
	fflush(stdout);
}

int main(void)
{
	double cp[N];		/* Function input values */
	double s[N];		/* Search area */
	double err;
	int j;
	int nprint = 0;		/* Itteration debugging print = off */
	int rc;

	error_program = "tpowell";	/* Set global error reporting string */
	check_if_not_interactive();

	/*	 The following starting values provide a rough solution. */
	for (j = 0; j < N; j++) {
		cp[j] = -1.f;
		s[j] = 0.9;
	}

	nprint = 0;

	/*	 Set tol to the square root of the machine precision. */
	/*	 Unless high precision solutions are required, */
	/*	 this is the recommended setting. */

	rc = conjgrad(
		&err,
		N, 				/* Dimentionality */
		cp,				/* Initial starting point */
		s,				/* Size of initial search area */
		0.00000001,		/* Tollerance of error change to stop on */
		1000,			/* Maximum iterations allowed */
		fcn, 			/* Error function to evaluate */
		dfcn,			/* Partial derivative function */
		NULL,			/* Opaque data needed by function */
		progress,		/* Progress callback */
		NULL			/* Context for callback */
	);


	fprintf(stdout,"Status = %d, final approximate solution err = %f:\n",rc,err);
	for (j = 0; j < N; j++) {
		fprintf(stdout,"cp[%d] = %e, expect %e\n",j,cp[j],expect[j]);
	}

	return 0;
} /* main() */

/* Function being minimized */
double fcn(		/* Return function value */
void *fdata,	/* Opaque data pointer */
double tp[]		/* Multivriate input value */
) {
	double err, tt;
	double temp, temp1, temp2;
	int k;

	/* Function Body */
	err = 0.0;
	for (k = 0; k < N; ++k) {
		temp = (3.0 - 2.0 * tp[k]) * tp[k];
		temp1 = 0.0;
		if (k != 0) {
			temp1 = tp[k-1];
		}
		temp2 = 0.0;
		if (k != ((N)-1))
			temp2 = tp[k+1];
		tt = temp - temp1 - 2.0 * temp2 + 1.0;
		err += tt * tt;
	}
	err = sqrt(err);
//printf("Returning %16.14f\n",err);
	return err;
}


/* Compute aprox. forward difference */

#define JEPS 1.0e-8	/* Aprox. sqrt of machine precision */

static double dfcn(
void *fdata,
double dp[],
double tp[]
) {
	int i;
	double d, h, temp;

	d = fcn(fdata, tp);

	for (i = 0; i < N; i++) {
		temp = tp[i];

		h = JEPS * fabs(temp);
		if (h == 0.0)
			h = JEPS;
		tp[i] = temp + h;		/* Add delta */
		h = tp[i] - temp;		/* Actual delta with fp precision limits */

		dp[i] = (fcn(fdata, tp) - d)/h;

		tp[i] = temp;			/* Restore value */
	}

	return DFUNC_NRV;
}