[Numpy-discussion] Re: Numpy-discussion digest, Vol 1 #50 - 2 msgs

[Travis Oliphant]

> Dear Numerical Python users,
> 
>         I am new to the numerical python and extending python in C.
> I am making  a module  that involves the  construction of  complex
> matrices.  But first, I really want to understand how these matrices are
> constructed.
>  Here is an example function  that constructs  a matrix of size M and
> puts on each position a complex number "x+I y".   x and y are arguments
> when you call the function in python.
> 
>         My question:  Is this the right way of organising the
> construction of a  complex matrix. Are there easier ways?
>         Can I construct the matrix  directly in  "result->data"??
> 

Yes, you can create the array, point a pointer to "result->data" and fill
it in.  Internally, when the array is created an equivalent malloc is
performed.


I've changed your code below to eliminate the unecessary copying.
> 
> 
> static PyObject* matrix(PyObject *self, PyObject *args){
>   double x,y;
>   int size;
>   int M,n,m;
>   PyArrayObject *result;
>   int dimensions[2];
>   Py_complex *data;
>   Py_complex p;
>   if(!PyArg_ParseTuple(args,"idd",&M,&x,&y))
>     return NULL;
>   dimensions[0] = M;
>   dimensions[1] = M;

>   result = (PyArrayObject
> *)PyArray_FromDims(2,dimensions,PyArray_CDOUBLE);

>   data = result->data;
>   for(n=0;n < M;n++){
>     for(m=0; m<M; m++){
>       p.real=x;
>       p.imag=y;
>       data[n*M+m] = p;
>     }
>   }

>   return PyArray_Return(result);return
> PyComplex_FromDoubles(data[1].real,data[1].imag);
>   free(data);
> }
> 


Welcome to the wonderful world of NumPy.

-Travis