A^TA + B?

[Zhifeng Sheng]

Dear all

I would like to implement B = A^TA + B.

And the transpose multiplication can be done with the following function,

PetscErrorCode PETSCMAT_DLLEXPORT MatMatMultTranspose(Mat A,Mat B,MatReuse scall,PetscReal fill,Mat *C) 

since I would like to save some memory, I don't want to create an 
intermediate matrix. In the above function, the discription of

the argument "scall" is not clear, I know that MAT_INITIAL_MATRIX will 
create a new empty matrix and the result will be stored.

what about MAT_REUSE_MATRIX ?  does it mean that the C matrix will be 
added with the result?

Thank you
Best regards
Zhifeng Sheng