Confused with pdpotrf arguments

Question

I want to do a Cholesky factorization in a distributed environment. For that purpose, I use pdpotrf(). However, I am struggling understanding the parameters needed by the function and they provide no C example on how to use it (and an example would be really great to have).

Assume I have a NxX matrix I want to factorize. Then, what values should the parameters have? uplo, a and info are well defined in my mind. How about the rest?

n should be equal to N I would say. However, desca, ia and ja are the ones that confuse me. Moreover, desca is global and local, something that I can't understand. Can someone explain? Maybe with an approach-example (not necessarily code, since I want to understand, not just copy paste).

_{I do not know any Fortran.}

Answer 1

From this answer, we have:

IA and JA: those parameters are meant to provide the starting row and column of your global matrix inside a larger matrix. They are only relevant if you have a big matrix and only want the Cholesky decomp of a submatrix. In your case, IA and JA both have to be 1!

Again, from this answer, there exists a link, that describes desca: