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46 #include "gromacs/fft/fft.h"
47 #include "gromacs/utility/smalloc.h"
50 #define SWAP(a, b) tempr = (a); (a) = (b); (b) = tempr
52 void four1(real data[], int nn, int isign)
54 int n, mmax, m, j, istep, i;
55 double wtemp, wr, wpr, wpi, wi, theta;
60 for (i = 1; i < n; i += 2)
64 SWAP(data[j], data[i]);
65 SWAP(data[j+1], data[i+1]);
68 while (m >= 2 && j > m)
79 theta = 6.28318530717959/(isign*mmax);
80 wtemp = sin(0.5*theta);
81 wpr = -2.0*wtemp*wtemp;
85 for (m = 1; m < mmax; m += 2)
87 for (i = m; i <= n; i += istep)
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;
97 wr = (wtemp = wr)*wpr-wi*wpi+wr;
98 wi = wi*wpr+wtemp*wpi+wi;
106 static void realft(real data[], int n, int isign)
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;
112 theta = 3.141592653589793/(double) n;
123 wtemp = sin(0.5*theta);
124 wpr = -2.0*wtemp*wtemp;
129 for (i = 2; i <= n/2; i++)
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;
145 data[1] = (h1r = data[1])+data[2];
146 data[2] = h1r-data[2];
150 data[1] = c1*((h1r = data[1])+data[2]);
151 data[2] = c1*(h1r-data[2]);
156 static void twofft(real data1[], real data2[], real fft1[], real fft2[], int n)
159 real rep, rem, aip, aim;
161 nn3 = 1+(nn2 = 2+n+n);
162 for (j = 1, jj = 2; j <= n; j++, jj += 2)
164 fft1[jj-1] = data1[j];
169 fft1[2] = fft2[2] = 0.0;
170 for (j = 3; j <= n+1; j += 2)
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]);
187 void correl(real data1[], real data2[], int n, real ans[])
193 twofft(data1, data2, fft, ans, n);
195 for (i = 2; i <= n+2; i += 2)
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;
202 realft(ans, no2, -1);