[petsc-users] create a matrix in C++ constructor

[Matthew Knepley]

On Mon, Dec 21, 2009 at 5:01 PM, Umut Tabak <u.tabak at tudelft.nl> wrote:

> Dear all,
>
> I was trying to wrap around some Petsc code into a class, so that there is
> a neat interface and implementation, I got into a problem at the very
> beginning and did not understand the reason maybe some of you could help me
> to understand this.
>
> I have a Matrix A in the private section of my simple class.
>
> And I would like to create this matrix inside the class ctor. Whenever I
> call the MatCreate function I get a segmentation fault with
>

Without seeing the code, we cannot say anything, but I bet you misdeclared
A.

  Matt


> MatCreate(MPI_COMM_SELF, &A)
>
> I checked the documentation that the Matrices in Petsc are also pointers.
>
> The point I did not understand is that if there is a pointer member of a
> class, say
> ...
> private:
> int* b
> ...
>
> I can initialize that to null in the constructor and make the necessary
> allocation with some member functions. With the same reasoning I thought
> that If I do not apply similar null pointer assignment for the matrix(there
> is not such thing I suppose) that I would like to initialize in the ctor, I
> will get a segfault. I could not figure my way out and wondered when you
> write the topdown code. I mean in the code below,
>
> Mat A;
>
> MatCreate(MPI_COMM_SELF, &A);
> MatSetSizes(A, m, n, 0, 0);
> MatSetType(A,MATSEQAIJ);
>
> "Mat A" initializes the pointer to null internally, am I right? Is there
> sth similar for the above class situation or am I mistaken at some other
> point(which could be highly likely)?
>
> Any pointers are appreciated.
> Umut
>



-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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