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38 * Implement routines for integrating a data set
40 * \author David van der Spoel <david.vanderspoel@icm.uu.se>
44 #include "integrate.h"
49 #include "gromacs/math/vec.h"
50 #include "gromacs/utility/fatalerror.h"
52 /*! \brief Integrate a function and printe the integral value. */
53 real print_and_integrate(FILE *fp, int n, real dt, const real c[],
54 const real *fit, int nskip)
59 /* Use trapezoidal rule for calculating integral */
61 for (j = 0; (j < n); j++)
64 if (fp && (nskip == 0 || j % nskip == 0))
66 fprintf(fp, "%10.3f %10.5f\n", j*dt, c0);
70 sum += dt*(c0+c[j-1]);
78 for (j = 0; (j < n); j++)
80 if (nskip == 0 || j % nskip == 0)
82 fprintf(fp, "%10.3f %10.5f\n", j*dt, fit[j]);
91 /*! \brief Compute and return the integral of a function. */
92 real evaluate_integral(int n, const real x[], const real y[],
93 const real dy[], real aver_start,
96 double sum, sum_var, w;
97 double sum_tail = 0, sum2_tail = 0;
100 /* Use trapezoidal rule for calculating integral */
103 gmx_fatal(FARGS, "Evaluating integral: n = %d (file %s, line %d)",
104 n, __FILE__, __LINE__);
109 for (j = 0; (j < n); j++)
114 w += 0.5*(x[j] - x[j-1]);
118 w += 0.5*(x[j+1] - x[j]);
123 /* Assume all errors are uncorrelated */
124 sum_var += sqr(w*dy[j]);
127 if ((aver_start > 0) && (x[j] >= aver_start))
130 sum2_tail += sqrt(sum_var);
137 sum = sum_tail/nsum_tail;
138 /* This is a worst case estimate, assuming all stddev's are correlated. */
139 *stddev = sum2_tail/nsum_tail;
143 *stddev = sqrt(sum_var);