query on psgbtrf parameters

[gajjar]

Hi,
I have a question regarding the ipiv parameter for psgbtrf in ScaLapack. In the ScaLapack book it says
IPIV is an integer array of dimension >= Desca(NB). NB is not explained but I am assuming NB refers to no of blocks. Fo the narrow band routines desca is of dimension at least 7 if dtype is 501, and much smaller than NB. So I dont understand this link with Desca(NB). What is the recommened dimension for IPIV ?

Jitesh Gajjar