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46 #include "gmx_fatal.h"
49 /* The grid sizes below are based on timing of a 3D cubic grid in fftw
50 * compiled with SSE using 4 threads in fft5d.c.
51 * A grid size is removed when a larger grid is faster.
54 /* Small grid size array */
56 const int grid_init[g_initNR] = { 6,8,10,12,14,16,20,24,25,28,32,36,40,42,44 };
58 /* For larger grid sizes, a prefactor with any power of 2 can be added.
59 * Only sizes divisible by 4 should be used, 90 is allowed, 140 not.
62 const int grid_base[g_baseNR] = { 45,48,50,52,54,56,60,64,70,72,75,80,81,84 };
64 real calc_grid(FILE *fp,matrix box,real gr_sp,
65 int *nx,int *ny,int *nz)
74 if ((*nx <= 0 || *ny <= 0 || *nz <= 0) && gr_sp <= 0)
76 gmx_fatal(FARGS,"invalid fourier grid spacing: %g",gr_sp);
79 if (grid_base[g_baseNR-1] % 4 != 0)
81 gmx_incons("the last entry in grid_base is not a multiple of 4");
84 /* New grid calculation setup:
86 * To maintain similar accuracy for triclinic PME grids as for rectangular
87 * ones, the max grid spacing should set along the box vectors rather than
88 * cartesian X/Y/Z directions. This will lead to slightly larger grids, but
89 * it is much better than having to go to pme_order=6.
91 * Thus, instead of just extracting the diagonal elements to box_size[d], we
92 * now calculate the cartesian length of the vectors.
94 * /Erik Lindahl, 20060402.
101 box_size[d] += box[d][i]*box[d][i];
103 box_size[d] = sqrt(box_size[d]);
110 if ((*nx<=0) || (*ny<=0) || (*nz<=0))
114 fprintf(fp,"Calculating fourier grid dimensions for%s%s%s\n",
115 *nx > 0 ? "":" X",*ny > 0 ? "":" Y",*nz > 0 ? "":" Z");
124 nmin = (int)(box_size[d]/gr_sp + 0.999);
127 if (grid_init[i] >= nmin)
129 /* Take the smallest possible grid in the list */
130 while (i > 0 && grid_init[i-1] >= nmin)
138 /* Determine how many pre-factors of 2 we need */
141 while (fac2*grid_base[i-1] < nmin)
145 /* Find the smallest grid that is >= nmin */
148 try = fac2*grid_base[i];
149 /* We demand a factor of 4, avoid 140, allow 90 */
150 if (((try % 4 == 0 && try != 140) || try == 90) &&
161 spacing[d] = box_size[d]/n[d];
162 if (spacing[d] > max_spacing)
164 max_spacing = spacing[d];
172 fprintf(fp,"Using a fourier grid of %dx%dx%d, spacing %.3f %.3f %.3f\n",
173 *nx,*ny,*nz,spacing[XX],spacing[YY],spacing[ZZ]);