[Numpy-discussion] Returning a 2-D PyArrayObject

[Amitha P]

Hi all,
I am new to Python/Python extension programming. I am
writing a c-extension to python which takes a
3-Dimensional array object and returns the
2Dimensional array object. 
The c function returns the 2-D array and converts into
Python object, but the 2D python array object doesnot
contain the correct values, it's priting out some
irrevelent values. I could successfully return single
dimension Python array object but I am not able to
return 2D python array object. I am attaching the
code. Please look at it and point out the errors. 
Thank you very much..

-------------------------------------------------------
CMATRIXMUL16.c - This takes the array (the python 3D
array) and returns the 2D array
------------------------------------------------------
#include <stdio.h>
#include <math.h>

 float* cmatrixmul16(float *array,float *paddarr, int
n,int r,int col,float
**store)
{
 int i,j,k;
 int devices;
 int pathpoints;
 int column;
 int len;
 float sum;
 float **a,**b,**c,**d;
 float *temp;

 static float **tracematrix; 
 tracematrix = store;

 pathpoints=r;
 column = col;
 devices= n;
 len = pathpoints*2;

 temp = (float *)malloc( len* sizeof(float));
 sum =0.0;
 
 a = (float **)malloc(devices * sizeof(float));
 b = (float **)malloc(devices * sizeof(float));
 c = (float **)malloc(devices * sizeof(float));
 d = (float **)malloc(devices * sizeof(float));


 for(i=0;i<devices;i++)
 {
  a[i] = (float *)malloc(pathpoints*sizeof(float));
  b[i] = (float *)malloc(pathpoints*sizeof(float));
  c[i] = (float *)malloc(pathpoints*sizeof(float));
  d[i] = (float *)malloc(pathpoints*sizeof(float));
 }

 for(k=0;k<devices;k++){
 for(i=0;i<pathpoints;i++)
   {
    a[k][i] =
(*(array+k*pathpoints*column+i*column+0))*(1.0/sqrt(2.0));
    b[k][i] =
(*(array+k*pathpoints*column+i*column+1))*(1.0/sqrt(2.0));
    c[k][i] =
(*(array+k*pathpoints*column+i*column+2))*(1.0/sqrt(2.0));
    d[k][i] =
(*(array+k*pathpoints*column+i*column+3))*(1.0/sqrt(2.0));

    tracematrix[k][i] =
a[k][i]*a[k][i]+b[k][i]*b[k][i];
    tracematrix[k][pathpoints+i] =
c[k][i]*c[k][i]+d[k][i]*d[k][i];
   }
 fprintf(stderr,"tracematrix: %f\n",
tracematrix[k][0]);
 }
 for(i=0;i<devices;i++)
 {
  free(a[i]);
  free(b[i]);
  free(c[i]);
  free(d[i]);
  }
 free(a);
 free(b);
 free(c);
 free(d);
return (float *)tracematrix;

}
------------------------------------------------------

This is the module which calls the function
_tests16module.c
-------------------------------------------------------

#include <Python.h>
#include <arrayobject.h>
#include <math.h>
static PyObject * Py_arraytest1 (PyObject *, PyObject
*);
static char _tests17_module_doc[] ="tests11: module
documentation";
static char arraytest1__doc__[]= "mytest:function
documentation";


/********************************Python symbol table
*****************************************/
static PyMethodDef _tests17_methods[] = {

  {"arraytest1"  , (PyCFunction)Py_arraytest1 ,
METH_VARARGS,arraytest1__doc__
},
  {NULL, (PyCFunction)NULL,0,NULL }  /* terminates the
list of methods */
};
/*********************************End of Symbol table
***************************************/



void init_tests17()
{
  /* We will be using C-functions defined in the array
module.  So we
   * need to be sure that the shared library defining
these functions
   * is loaded. */
  import_array();
  (void) Py_InitModule4(
                        "_tests17",          /* module
name */
                         _tests17_methods,    /*
structure containing python
symbol info */
                         _tests17_module_doc, /*
module documentation string */
                        (PyObject *) NULL,
                        PYTHON_API_VERSION);
}
/*function to calculate the product of two arrays */


static PyObject *
Py_arraytest1(PyObject *self, PyObject *args)
{
  PyArrayObject *array, *paddarr, *product;
  char *c;
  int n,r,col,i,j,k;
  int dimensions[2];
  float **store;
  
  if (!PyArg_ParseTuple(args, "O!O!",
                           &PyArray_Type,
&array,&PyArray_Type,&paddarr))

    return NULL;
 /* The arguments are the 3-D array and the 1-Dpaddarr
*/

 n = (long) array->dimensions[0];
 r = (long) array->dimensions[1];
 col = (long) array->dimensions[2];

 store = (float **)malloc(n*sizeof(float));
 for(i=0;i<n;i++)
  store[i]=(float *)malloc(2*r*sizeof(float));

c=  (char*)cmatrixmul16((float *)array->data,(float
*)paddarr->data,n,r,col,store);
dimensions[0] = n;
dimensions[1] = 2*r;

product = (PyArrayObject *)PyArray_FromDimsAndData(2,
dimensions,
PyArray_FLOAT,c);

PyArray_Return(product);
}



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