Hi!

Your question is not so easy. Despite of PARDISO, DSS doesn't support simultaneous processing of several matrices with one and the same sparse structure. So, it is not possible to examine your situation without working example. Could you provide us with your test case?
If I am not mistaken you want to solve two matrices with one and the same sparse structure at the same time. There are two possible ways for doing this.
First, different matrices with their LU factors can be stored in separate handles. So, you have to reorder, factorize and solve each matrix separately. Of course, in this case memory is used not effectively, because many internal PARDISO arrays are one and the same in both cases.
Second, this problem can be solved by PARDISO which support simultaneous solving of several matrices which have the same sparse structure. This is the best way from the memory utilization point of view. Please see MKL reference manual for details (namely pay attention to maxfct and mnum parameters of PARDISO).

With best regards,
Sergey