covariance_fields_spatial.c

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00001 /* ***************************************************** */
00002 /* Compute the spatial covariance of two fields.         */
00003 /* covariance_fields_spatial.c                           */
00004 /* ***************************************************** */
00005 /* Author: Christian Page, CERFACS, Toulouse, France.    */
00006 /* ***************************************************** */
00011 /* LICENSE BEGIN
00012 
00013 Copyright Cerfacs (Christian Page) (2015)
00014 
00015 christian.page@cerfacs.fr
00016 
00017 This software is a computer program whose purpose is to downscale climate
00018 scenarios using a statistical methodology based on weather regimes.
00019 
00020 This software is governed by the CeCILL license under French law and
00021 abiding by the rules of distribution of free software. You can use, 
00022 modify and/ or redistribute the software under the terms of the CeCILL
00023 license as circulated by CEA, CNRS and INRIA at the following URL
00024 "http://www.cecill.info". 
00025 
00026 As a counterpart to the access to the source code and rights to copy,
00027 modify and redistribute granted by the license, users are provided only
00028 with a limited warranty and the software's author, the holder of the
00029 economic rights, and the successive licensors have only limited
00030 liability. 
00031 
00032 In this respect, the user's attention is drawn to the risks associated
00033 with loading, using, modifying and/or developing or reproducing the
00034 software by the user in light of its specific status of free software,
00035 that may mean that it is complicated to manipulate, and that also
00036 therefore means that it is reserved for developers and experienced
00037 professionals having in-depth computer knowledge. Users are therefore
00038 encouraged to load and test the software's suitability as regards their
00039 requirements in conditions enabling the security of their systems and/or 
00040 data to be ensured and, more generally, to use and operate it in the 
00041 same conditions as regards security. 
00042 
00043 The fact that you are presently reading this means that you have had
00044 knowledge of the CeCILL license and that you accept its terms.
00045 
00046 LICENSE END */
00047 
00048 
00049 
00050 
00051 
00052 
00053 
00054 #include <utils.h>
00055 
00057 void
00058 covariance_fields_spatial(double *cov, double *buf1, double *buf2, short int *mask, int t1, int t2, int ni, int nj) {
00059 
00071   int i; /* Loop counter */
00072   int j; /* Loop counter */
00073   int pts = 0; /* Points counter */
00074   int num = 0; /* Elements counter */
00075 
00076   double sum1; /* Temporary sum for buf1 */
00077   double sum2; /* Temporary sum for buf2 */
00078   double mean1; /* Mean for buf1 */
00079   double mean2; /* Mean for buf2 */
00080 
00081   /* Compute spatial covariance, optionally using a mask */
00082   if (mask == NULL) {
00083 
00084     /* Calculate mean of each field */
00085     sum1 = 0.0;
00086     sum2 = 0.0;
00087     for (j=0; j<nj; j++)
00088       for (i=0; i<ni; i++) {
00089         sum1 += buf1[i+j*ni+t1*ni*nj];
00090         sum2 += buf2[i+j*ni+t2*ni*nj];
00091       }
00092     mean1 = sum1 / (double) (ni*nj);
00093     mean2 = sum2 / (double) (ni*nj);
00094 
00095     /* Calculate spatial covariance */
00096     *cov = 0.0;
00097     num = 0;
00098     for (j=0; j<nj; j++)
00099       for (i=0; i<ni; i++) {
00100         /* Sum of the squares (remove mean) */
00101         (*cov) += ( ( (buf1[i+j*ni+t1*ni*nj] - mean1) * (buf2[i+j*ni+t2*ni*nj] - mean2) ) - (*cov)) / (double) (num + 1);
00102         num++;
00103       }
00104   }
00105   else {
00106     /* Calculate mean of each field */
00107     sum1 = 0.0;
00108     sum2 = 0.0;
00109     pts = 0;
00110     for (j=0; j<nj; j++)
00111       for (i=0; i<ni; i++)
00112         if (mask[i+j*ni] == 1) {
00113           sum1 += buf1[i+j*ni+t1*ni*nj];
00114           sum2 += buf2[i+j*ni+t2*ni*nj];
00115           pts++;
00116         }
00117     mean1 = sum1 / (double) (pts);
00118     mean2 = sum2 / (double) (pts);
00119 
00120     /* Calculate spatial covariance */
00121     *cov = 0.0;
00122     num = 0;
00123     for (j=0; j<nj; j++)
00124       for (i=0; i<ni; i++) {
00125         if (mask[i+j*ni] == 1) {
00126           /* Sum of the squares (remove mean) */
00127           (*cov) += ( ( (buf1[i+j*ni+t1*ni*nj] - mean1) * (buf2[i+j*ni+t2*ni*nj] - mean2) ) - (*cov)) / (double) (num + 1);
00128           num++;
00129         }
00130       }
00131   }
00132 }

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