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/*----------------------------------------------------------------------------
ADOL-C -- Automatic Differentiation by Overloading in C++
File: helm-diff-exam.cpp
Revision: $Id$
Contents: example for Helmholtz energy example
Computes gradient using divide differences
Copyright (c) Andrea Walther, Andreas Griewank, Andreas Kowarz,
Hristo Mitev, Sebastian Schlenkrich, Jean Utke, Olaf Vogel
This file is part of ADOL-C. This software is provided as open source.
Any use, reproduction, or distribution of the software constitutes
recipient's acceptance of the terms of the accompanying license file.
---------------------------------------------------------------------------*/
/****************************************************************************/
/* INCLUDES */
#include <sys/types.h>
#include <stdio.h>
#include <math.h>
#include <cstdlib>
/****************************************************************************/
/* CONSTANTS & VARIABLES */
#define delta 0.000001
#define TE 0.01
#define R sqrt(2.0)
/****************************************************************************/
/* HELMHOLTZ ENERGY */
double energy( int n, double x[], double bv[] ) {
double he, xax, bx, tem;
int i,j;
xax = 0;
bx = 0;
he = 0;
for (i=0; i<n; i++) {
he += x[i]*log(x[i]);
bx += bv[i]*x[i];
tem = (2.0/(1.0+i+i))*x[i];
for (j=0; j<i; j++)
tem += (1.0/(1.0+i+j))*x[j];
xax += x[i]*tem;
}
xax *= 0.5;
he = 1.3625E-3*(he-TE*log(1.0-bx));
he = he - log((1+bx*(1+R))/(1+bx*(1-R)))*xax/bx;
return he;
}
/****************************************************************************/
/* MAIN */
/*
This program computes first order directional derivatives
for the helmholtz energy function */
int main(int argc, char *argv[]) {
int nf, n, j, l;
double result1, result2;
double q, jd, r;
double *x, *bv;
fprintf(stdout,"HELM-DIFF-EXAM (ADOL-C Example)\n\n");
fprintf(stdout," # of independents/10 =? \n ");
scanf("%d",&nf);
/*--------------------------------------------------------------------------*/
n = 10 * nf; /* Initilizations */
x = (double*) malloc(n*sizeof(double));
bv = (double*) malloc(n*sizeof(double));
r = 1.0/n;
for (j=0; j<n; j++) {
jd = j;
bv[j] = 0.02*(1.0+fabs(sin(jd)));
x[j] = r*sqrt(1.0+jd);
}
/*--------------------------------------------------------------------------*/
result2 = energy(n,x,bv); /* basepoint */
fprintf(stdout,"%14.6E -- energy\n",result2);
/*--------------------------------------------------------------------------*/
for (l=0; l<n; l++) /* directional derivatives */
{ x[l] = x[l]+delta;
result1 = energy(n,x,bv);
x[l] = x[l]-delta;
q = (result1-result2)/delta;
fprintf(stdout,"%3d: %14.6E, \n",l,q);
}
fprintf(stdout,"%14.6E -- energy\n",result2);
free((char*) bv);
free((char*) x);
return 0;
}
/****************************************************************************/
/* THAT'S ALL */
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