src/gromacs/gmxlib/calcgrid.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) 2001-2004, The GROMACS development team.
   6  * Copyright (c) 2012,2014, 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 #include "gmxpre.h"
  38
  39 #include "gromacs/legacyheaders/calcgrid.h"
  40
  41 #include <math.h>
  42
  43 #include "gromacs/legacyheaders/typedefs.h"
  44 #include "gromacs/utility/fatalerror.h"
  45 #include "gromacs/utility/smalloc.h"
  46
  47 /* The grid sizes below are based on timing of a 3D cubic grid in fftw
  48  * compiled with SSE using 4 threads in fft5d.c.
  49  * A grid size is removed when a larger grid is faster.
  50  */
  51
  52 /* Small grid size array */
  53 #define g_initNR 15
  54 const int grid_init[g_initNR] = { 6, 8, 10, 12, 14, 16, 20, 24, 25, 28, 32, 36, 40, 42, 44 };
  55
  56 /* For larger grid sizes, a prefactor with any power of 2 can be added.
  57  * Only sizes divisible by 4 should be used, 90 is allowed, 140 not.
  58  */
  59 #define g_baseNR 14
  60 const int grid_base[g_baseNR] = { 45, 48, 50, 52, 54, 56, 60, 64, 70, 72, 75, 80, 81, 84 };
  61
  62 real calc_grid(FILE *fp, matrix box, real gr_sp,
  63                int *nx, int *ny, int *nz)
  64 {
  65     int  d, n[DIM];
  66     int  i;
  67     rvec box_size;
  68     int  nmin, fac2, try;
  69     rvec spacing;
  70     real max_spacing;
  71
  72     if ((*nx <= 0 || *ny <= 0 || *nz <= 0) && gr_sp <= 0)
  73     {
  74         gmx_fatal(FARGS, "invalid fourier grid spacing: %g", gr_sp);
  75     }
  76
  77     if (grid_base[g_baseNR-1] % 4 != 0)
  78     {
  79         gmx_incons("the last entry in grid_base is not a multiple of 4");
  80     }
  81
  82     /* New grid calculation setup:
  83      *
  84      * To maintain similar accuracy for triclinic PME grids as for rectangular
  85      * ones, the max grid spacing should set along the box vectors rather than
  86      * cartesian X/Y/Z directions. This will lead to slightly larger grids, but
  87      * it is much better than having to go to pme_order=6.
  88      *
  89      * Thus, instead of just extracting the diagonal elements to box_size[d], we
  90      * now calculate the cartesian length of the vectors.
  91      *
  92      * /Erik Lindahl, 20060402.
  93      */
  94     for (d = 0; d < DIM; d++)
  95     {
  96         box_size[d] = 0;
  97         for (i = 0; i < DIM; i++)
  98         {
  99             box_size[d] += box[d][i]*box[d][i];
 100         }
 101         box_size[d] = sqrt(box_size[d]);
 102     }
 103
 104     n[XX] = *nx;
 105     n[YY] = *ny;
 106     n[ZZ] = *nz;
 107
 108     if ((*nx <= 0) || (*ny <= 0) || (*nz <= 0))
 109     {
 110         if (NULL != fp)
 111         {
 112             fprintf(fp, "Calculating fourier grid dimensions for%s%s%s\n",
 113                     *nx > 0 ? "" : " X", *ny > 0 ? "" : " Y", *nz > 0 ? "" : " Z");
 114         }
 115     }
 116
 117     max_spacing = 0;
 118     for (d = 0; d < DIM; d++)
 119     {
 120         if (n[d] <= 0)
 121         {
 122             nmin = (int)(box_size[d]/gr_sp + 0.999);
 123
 124             i = g_initNR - 1;
 125             if (grid_init[i] >= nmin)
 126             {
 127                 /* Take the smallest possible grid in the list */
 128                 while (i > 0 && grid_init[i-1] >= nmin)
 129                 {
 130                     i--;
 131                 }
 132                 n[d] = grid_init[i];
 133             }
 134             else
 135             {
 136                 /* Determine how many pre-factors of 2 we need */
 137                 fac2 = 1;
 138                 i    = g_baseNR - 1;
 139                 while (fac2*grid_base[i] < nmin)
 140                 {
 141                     fac2 *= 2;
 142                 }
 143                 /* Find the smallest grid that is >= nmin */
 144                 do
 145                 {
 146                     try = fac2*grid_base[i];
 147                     /* We demand a factor of 4, avoid 140, allow 90 */
 148                     if (((try % 4 == 0 && try != 140) || try == 90) &&
 149                         try >= nmin)
 150                     {
 151                         n[d] = try;
 152                     }
 153                     i--;
 154                 }
 155                 while (i > 0);
 156             }
 157         }
 158
 159         spacing[d] = box_size[d]/n[d];
 160         if (spacing[d] > max_spacing)
 161         {
 162             max_spacing = spacing[d];
 163         }
 164     }
 165     *nx = n[XX];
 166     *ny = n[YY];
 167     *nz = n[ZZ];
 168     if (NULL != fp)
 169     {
 170         fprintf(fp, "Using a fourier grid of %dx%dx%d, spacing %.3f %.3f %.3f\n",
 171                 *nx, *ny, *nz, spacing[XX], spacing[YY], spacing[ZZ]);
 172     }
 173
 174     return max_spacing;
 175 }