In a
previous post I explained how to work with passing in a list of data and calculating its mean value.
In this post we are going to pass in two arguments, a row and column value, and return a matrix with that
specified dimension.
Here is the code (CreateMatrix.c):
#include "WolframLibrary.h"
DLLEXPORT int CreateMatrix(WolframLibraryData libData, mint Argc, MArgument *Args, MArgument Res) {
mint row,col,rows,cols,count;
MTensor out;
mint out_type = MType_Integer;
mint out_rank = 2 ;
mint out_dims[2];
mint* out_data;
int err;
rows = MArgument_getInteger(Args[0]);
cols = MArgument_getInteger(Args[1]);
out_dims[0] = rows;
out_dims[1] = cols;
err = libData->MTensor_new( out_type, out_rank, out_dims, &out );
out_data = libData->MTensor_getIntegerData(out);
count=1;
for(row=0; row<rows; row++) {
for(col=0; col<cols; col++) {
out_data[col+cols*row] = count++;
}
}
MArgument_setMTensor(Res,out);
return LIBRARY_NO_ERROR;
}
The key new functionality in this code is the creation of an MTensor using libData->MTensor_new and filling the
rows and columns of that tensor with (increasing) integer values, using 'count'.
To create a new tensor you need to specify the type (MType_Integer), the rank (2 for a matrix) and the dimensions (rows and cols in this case).
To fill the matrix you need to get the (uninitialized) integer data out of the tensor, using libData->MTensor_getIntgerData. Then you can fill the data with a nested for loop over the rows and columns.
The Wolfram Language build and function loading code will now need to specify that we are going to pass in two arguments, a rows
and a columns argument and that we are going to return a 2 dimensional integer tensor (CreateMatrix.m):
Needs["CCompilerDriver`"];
lib = CreateLibrary[{"CreateMatrix.c"},"CreateMatrix"];
CreateMatrix = LibraryFunctionLoad[lib,"CreateMatrix",{Integer,Integer},{Integer,2}];
Now we can try running this code in the Wolfram Language:
Mathematica 10.0 for Microsoft Windows (64-bit)
Copyright 1988-2013 Wolfram Research, Inc.
In[1]:= Get["CreateMatrix.m"]
In[2]:= CreateMatrix[3,4] // Grid
Out[2]= 1 2 3 4
5 6 7 8
9 10 11 12
In[3]:= CreateMatrix[3,12] // Grid
Out[3]= 1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24
25 26 27 28 29 30 31 32 33 34 35 36
In the next post we will take a look at how to
work with complex numbers.
