Matlab external Interface : Mat-File generation program

　　Matlab external Interface這玩意的中文不知道是什麼，感覺是Matlab外掛程式一類的東西。我用c++寫了一個函數可以產生一個巨大的矩陣。但是這個矩陣的svd分解我可不想再用c++寫了。於是我想把這個大矩陣匯入matlab的*.mat檔案中，讓matlab的svd命令來計算這個矩陣的svd分解。Matlab external Interface允許我寫一個可以產生matlab Mat檔案的c++程式。當然要包含matlab的標頭檔 "mat.h",同時還要與matlab的*.so(linux) *.lib(win32)等庫檔案連結。可執行檔的編譯和連結功能可以有mex命令自動實現，不用自己寫Makefile。我自己嘗試寫一個makefile但是沒有編譯成功。先貼出My Code在細講吧：

  1 #include <stdio.h>
  2 #include <string.h> /* For strcmp() */
  3 #include <stdlib.h> /* For EXIT_FAILURE, EXIT_SUCCESS */
  4 #include <vector> /* For STL */
  5 #include <iostream>
  6 #include <fstream>
  7 #include "mat.h"
  8 
  9 using namespace std;
 10 
 11 #define BUFSIZE 256
 12 
 13 int main() {
 14   MATFile *pmat;
 15   mxArray *pa1;// *pa2, *pa3;
 16   fstream infile("outputMat", ios::in);
 17   if( ! infile.is_open() )
 18   {
 19       cout << "no file" << endl;
 20       return -1;
 21   }
 22   std::vector<int> myInts;
 23   myInts.push_back(1);
 24   myInts.push_back(2);
 25   printf("Accessing a STL vector: %d\n", myInts[1]);
 26 
 27   //double data[9] = { 1.0, 4.0, 7.0, 2.0, 5.0, 8.0, 3.0, 6.0, 9.0 };
 28   double *data = NULL;
 29   const char *file = "mattest.mat";
 30   char str[BUFSIZE];
 31   int status;
 32   int width,height;
 33   infile >> height;
 34   infile >> width;
 35   cout << height;
 36   data = (double*)malloc(sizeof(double)*width*height);
 37   if( !data )
 38   {
 39       cout << "Out of Memory !" << endl;
 40       return -1;
 41   }
 42   for(unsigned i = 0; i < width * height; i++)
 43   {
 44       float tmp;
 45       infile >> tmp;
 46       data[i] = (double)tmp;
 47       //cout << data[i] << " ";
 48   }
 49   infile.close();
 50 
 51   printf("Creating file %s...\n\n", file);
 52   pmat = matOpen(file, "w");
 53   if (pmat == NULL) {
 54     printf("Error creating file %s\n", file);
 55     printf("(Do you have write permission in this directory?)\n");
 56     return(EXIT_FAILURE);
 57   }
 58 
 59   pa1 = mxCreateDoubleMatrix(width,height,mxREAL);
 60   if (pa1 == NULL) {
 61       printf("%s : Out of memory on line %d\n", __FILE__, __LINE__); 
 62       printf("Unable to create mxArray.\n");
 63       return(EXIT_FAILURE);
 64   }
 65   
 66   status = matPutVariable(pmat, "GlobalDouble", pa1);
 67   if (status != 0) {
 68       printf("%s :  Error using matPutVariable on line %d\n", __FILE__, __LINE__);
 69       return(EXIT_FAILURE);
 70   }  
 71   
 72     
 73    
 74   /*
 75    * Ooops! we need to copy data before writing the array.  (Well,
 76    * ok, this was really intentional.) This demonstrates that
 77    * matPutVariable will overwrite an existing array in a MAT-file.
 78 */
 79   memcpy((void *)(mxGetPr(pa1)), (void *)data, sizeof(double)*width*height);
 80   status = matPutVariable(pmat, "GlobalDouble", pa1);
 81   if (status != 0) {
 82       printf("%s :  Error using matPutVariable on line %d\n", __FILE__, __LINE__);
 83       return(EXIT_FAILURE);
 84   } 
 85   
 86   /* clean up */
 87   mxDestroyArray(pa1);
 88  
 89   if (matClose(pmat) != 0) {
 90     printf("Error closing file %s\n",file);
 91     return(EXIT_FAILURE);
 92   }
 93 
 94   /*
 95    * Re-open file and verify its contents with matGetVariable
 96 */
 97   pmat = matOpen(file, "r");
 98   if (pmat == NULL) {
 99     printf("Error reopening file %s\n", file);
100     return(EXIT_FAILURE);
101   }
102 
103   /*
104    * Read in each array we just wrote
105 */
106   pa1 = matGetVariable(pmat, "GlobalDouble");
107   if (pa1 == NULL) {
108     printf("Error reading existing matrix LocalDouble\n");
109     return(EXIT_FAILURE);
110   }
111   if (mxGetNumberOfDimensions(pa1) != 2) {
112     printf("Error saving matrix: result does not have two dimensions\n");
113     return(EXIT_FAILURE);
114   }
115 
116     
117   
118   /* clean up before exit */
119   mxDestroyArray(pa1);
120   
121   if (matClose(pmat) != 0) {
122     printf("Error closing file %s\n",file);
123     return(EXIT_FAILURE);
124   }
125   printf("Done\n");
126   return(EXIT_SUCCESS);
127 }

　　代碼的第33～48行是讀取一個寫有矩陣資料的檔案，該檔案的前兩個int是這個矩陣的行和列。之後就是 行x列 個float型的資料。都讀入一個double型的數組中。59和66行的代碼就是matlab提供的API。使用這兩行代碼可以產生一個matlab矩陣。並給這個矩陣起個變數名。最後把之前存在double數組裡的資料拷貝到這個matlab矩陣中就可以了。在編譯這個代碼的時候，要使用mex命令。
　　開啟matlab，輸入 如下命令

mex('-v', '-f', ['matlabroot' '/bin/matopts.sh'], 'matcreat.cpp')

　　其中matcreat.cpp就是源檔案的名稱。matlabroot是matlab安裝的路徑。產生的可執行檔不一定能執行。我的系統是fedora x64，系統提示我缺少libmat.so。這是因為沒有設定好環境變數。在bash中輸入如下代碼就可以把環境變數設定好，每次啟動終端的時候都要如此設定！如果覺得麻煩就寫在~/.bashrc中，但是這樣在我的fedora15電腦上出現很多莫名其妙的狀況。所以不推薦。輸入的命令是：

$LD_LIBRARY_PATH=/home/local/MATLAB/R2011b/bin/glnxa64:/home/local/MATLAB/R2011b/sys/os/glnxa64:$LD_LIBRARY_PATH
$export LD_LIBRARY_PATH

這樣運行之後可以產生mattest.mat檔案，能正常匯入到matlab中。