src/gromacs/gmxana/correl.c

   1 /*
   2  * This file is part of the GROMACS molecular simulation package.
   3  *
   4  * Copyright (c) 1991-2000, University of Groningen, The Netherlands.
   5  * Copyright (c) 2001-2008, The GROMACS development team.
   6  * Copyright (c) 2013,2014, by the GROMACS development team, led by
   7  * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
   8  * and including many others, as listed in the AUTHORS file in the
   9  * top-level source directory and at http://www.gromacs.org.
  10  *
  11  * GROMACS is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public License
  13  * as published by the Free Software Foundation; either version 2.1
  14  * of the License, or (at your option) any later version.
  15  *
  16  * GROMACS is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with GROMACS; if not, see
  23  * http://www.gnu.org/licenses, or write to the Free Software Foundation,
  24  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
  25  *
  26  * If you want to redistribute modifications to GROMACS, please
  27  * consider that scientific software is very special. Version
  28  * control is crucial - bugs must be traceable. We will be happy to
  29  * consider code for inclusion in the official distribution, but
  30  * derived work must not be called official GROMACS. Details are found
  31  * in the README & COPYING files - if they are missing, get the
  32  * official version at http://www.gromacs.org.
  33  *
  34  * To help us fund GROMACS development, we humbly ask that you cite
  35  * the research papers on the package. Check out http://www.gromacs.org.
  36  */
  37
  38 #ifdef HAVE_CONFIG_H
  39 #include <config.h>
  40 #endif
  41
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include <math.h>
  45
  46 #include "gromacs/fft/fft.h"
  47 #include "gromacs/utility/smalloc.h"
  48 #include "correl.h"
  49
  50 #define SWAP(a, b) tempr = (a); (a) = (b); (b) = tempr
  51
  52 void four1(real data[], int nn, int isign)
  53 {
  54     int    n, mmax, m, j, istep, i;
  55     double wtemp, wr, wpr, wpi, wi, theta;
  56     real   tempr, tempi;
  57
  58     n = nn << 1;
  59     j = 1;
  60     for (i = 1; i < n; i += 2)
  61     {
  62         if (j > i)
  63         {
  64             SWAP(data[j], data[i]);
  65             SWAP(data[j+1], data[i+1]);
  66         }
  67         m = n >> 1;
  68         while (m >= 2 && j > m)
  69         {
  70             j  -= m;
  71             m >>= 1;
  72         }
  73         j += m;
  74     }
  75     mmax = 2;
  76     while (n > mmax)
  77     {
  78         istep = 2*mmax;
  79         theta = 6.28318530717959/(isign*mmax);
  80         wtemp = sin(0.5*theta);
  81         wpr   = -2.0*wtemp*wtemp;
  82         wpi   = sin(theta);
  83         wr    = 1.0;
  84         wi    = 0.0;
  85         for (m = 1; m < mmax; m += 2)
  86         {
  87             for (i = m; i <= n; i += istep)
  88             {
  89                 j          = i+mmax;
  90                 tempr      = wr*data[j]-wi*data[j+1];
  91                 tempi      = wr*data[j+1]+wi*data[j];
  92                 data[j]    = data[i]-tempr;
  93                 data[j+1]  = data[i+1]-tempi;
  94                 data[i]   += tempr;
  95                 data[i+1] += tempi;
  96             }
  97             wr = (wtemp = wr)*wpr-wi*wpi+wr;
  98             wi = wi*wpr+wtemp*wpi+wi;
  99         }
 100         mmax = istep;
 101     }
 102 }
 103
 104 #undef SWAP
 105
 106 static void realft(real data[], int n, int isign)
 107 {
 108     int    i, i1, i2, i3, i4, n2p3;
 109     real   c1 = 0.5, c2, h1r, h1i, h2r, h2i;
 110     double wr, wi, wpr, wpi, wtemp, theta;
 111
 112     theta = 3.141592653589793/(double) n;
 113     if (isign == 1)
 114     {
 115         c2 = -0.5;
 116         four1(data, n, 1);
 117     }
 118     else
 119     {
 120         c2    = 0.5;
 121         theta = -theta;
 122     }
 123     wtemp = sin(0.5*theta);
 124     wpr   = -2.0*wtemp*wtemp;
 125     wpi   = sin(theta);
 126     wr    = 1.0+wpr;
 127     wi    = wpi;
 128     n2p3  = 2*n+3;
 129     for (i = 2; i <= n/2; i++)
 130     {
 131         i4       = 1+(i3 = n2p3-(i2 = 1+(i1 = i+i-1)));
 132         h1r      = c1*(data[i1]+data[i3]);
 133         h1i      = c1*(data[i2]-data[i4]);
 134         h2r      = -c2*(data[i2]+data[i4]);
 135         h2i      = c2*(data[i1]-data[i3]);
 136         data[i1] = h1r+wr*h2r-wi*h2i;
 137         data[i2] = h1i+wr*h2i+wi*h2r;
 138         data[i3] = h1r-wr*h2r+wi*h2i;
 139         data[i4] = -h1i+wr*h2i+wi*h2r;
 140         wr       = (wtemp = wr)*wpr-wi*wpi+wr;
 141         wi       = wi*wpr+wtemp*wpi+wi;
 142     }
 143     if (isign == 1)
 144     {
 145         data[1] = (h1r = data[1])+data[2];
 146         data[2] = h1r-data[2];
 147     }
 148     else
 149     {
 150         data[1] = c1*((h1r = data[1])+data[2]);
 151         data[2] = c1*(h1r-data[2]);
 152         four1(data, n, -1);
 153     }
 154 }
 155
 156 static void twofft(real data1[], real data2[], real fft1[], real fft2[], int n)
 157 {
 158     int  nn3, nn2, jj, j;
 159     real rep, rem, aip, aim;
 160
 161     nn3 = 1+(nn2 = 2+n+n);
 162     for (j = 1, jj = 2; j <= n; j++, jj += 2)
 163     {
 164         fft1[jj-1] = data1[j];
 165         fft1[jj]   = data2[j];
 166     }
 167     four1(fft1, n, 1);
 168     fft2[1] = fft1[2];
 169     fft1[2] = fft2[2] = 0.0;
 170     for (j = 3; j <= n+1; j += 2)
 171     {
 172         rep         = 0.5*(fft1[j]+fft1[nn2-j]);
 173         rem         = 0.5*(fft1[j]-fft1[nn2-j]);
 174         aip         = 0.5*(fft1[j+1]+fft1[nn3-j]);
 175         aim         = 0.5*(fft1[j+1]-fft1[nn3-j]);
 176         fft1[j]     = rep;
 177         fft1[j+1]   = aim;
 178         fft1[nn2-j] = rep;
 179         fft1[nn3-j] = -aim;
 180         fft2[j]     = aip;
 181         fft2[j+1]   = -rem;
 182         fft2[nn2-j] = aip;
 183         fft2[nn3-j] = rem;
 184     }
 185 }
 186
 187 void correl(real data1[], real data2[], int n, real ans[])
 188 {
 189     int     no2, i;
 190     real    dum, *fft;
 191
 192     snew(fft, 2*n+1);
 193     twofft(data1, data2, fft, ans, n);
 194     no2 = n/2;
 195     for (i = 2; i <= n+2; i += 2)
 196     {
 197         dum      = ans[i-1];
 198         ans[i-1] = (fft[i-1]*dum+fft[i]*ans[i])/no2;
 199         ans[i]   = (fft[i]*dum-fft[i-1]*ans[i])/no2;
 200     }
 201     ans[2] = ans[n+1];
 202     realft(ans, no2, -1);
 203     sfree(fft);
 204 }