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.}

Ancilin

You first need to study how this package distributes matrices, after that you will know what do the arguments mean. You do not need Fortran. You do need to read the ScaLAPACK manual. – Hurwit

If I could find that, it would be great! Can't we say how the distribution happens from the parameters @VladimirF? – Ancilin

You must rtfm netlib.org/scalapack/slug/node35.html – Hurwit

@VladimirF believe it or not, yesterday night (when I was out), I thought I should google "distribute matrix in ScaLAPACK". And yes, should RTFM! Will investigate the link you gave. You may also wish to make an answer with that. – Ancilin

@VladimirF I did read it, but still I can't figure it out. I will continue searching and report back if necessary. – Ancilin

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:

Ancilin