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Hello,

Since I am unable to comment/reply/edit my previous post, I am starting a duplicate with updated info at the bottom of the post. I am sorry, but I couldn't think of any other alternative.

**ORIGINAL POST:**

I am trying to use PARDISO for solving a structurally symmetric complex matrix generated by a FEM scheme, and I am quite confused by its memory requirements.

When running PARDISO with a 144k equations matrix, I see a memory consumption up to 3GB in the factorization step. If I disable the permutation, by setting perm[i]=i in the perm array and iparm[4] = 1, it goes up to 5GB (I will use C++ 0-based indexing in this post as to avoid confusion).

I find this behavior to be a bit surprising, given that for symmetric real problems I normally see a negligible memory consumption for matrices around the same size.

Attached you can see the sparsity pattern of the input matrix

with the red color denoting non-zero positions (each block actually corresponds to ~15 equations).

With iparm[4] = 2 I was able to inspect the matrix after PARDISO's reordering, and its sparsity pattern is as follows

Is this memory consumption considered normal? This matrix is obtained from a really coarse mesh, so for any practical application I wouldn't be able to use PARDISO if that is the case (perhaps with OOC mode, with I wouldn't expected to be needed for systems this big).

I first had this results using 32bit interface of oneAPI MKL 2021, and I didn't get any different results by using the 64bit interface of both 2021 and 2023 MKLs. All the tests were performed in a C++ code compiled with gcc in a Linux environment.

Unfortunately I cannot post here an easy way to generate such results, as it would require to download and compile a C++ library.

If there is further information that I could provide in order to provide more insight to this problem, I would be really happy to do so.

Thank you in advance.

**UPDATE:**

The files can be obtained in this Google Drive link , and below one can see PARDISO's output.

Best regards,

Francisco

```
=== PARDISO is running in In-Core mode, because iparam(60)=0 ===
Percentage of computed non-zeros for LL^T factorization
1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 10 % 11 % 12 % 13 % 14 % 15 % 16 % 17 % 18 % 19 % 20 % 21 % 22 % 23 % 24 % 25 % 26 % 27 % 28 % 29 % 30 % 31 % 32 % 33 % 34 % 35 % 36 % 37 % 38 % 39 % 40 % 41 % 42 % 43 % 44 % 45 % 47 % 48 % 49 % 51 % 52 % 53 % 54 % 55 % 56 % 57 % 58 % 59 % 61 % 62 % 63 % 64 % 65 % 67 % 69 % 71 % 73 % 75 % 77 % 78 % 79 % 80 % 81 % 82 % 85 % 88 % 90 % 92 % 93 % 95 % 96 % 97 % 98 % 99 % 100 %
=== PARDISO: solving a complex structurally symmetric system ===
Matrix checker is turned ON
0-based array is turned ON
PARDISO double precision computation is turned ON
METIS algorithm at reorder step is turned ON
Single-level factorization algorithm is turned ON
Summary: ( starting phase is reordering, ending phase is factorization )
================
Times:
======
Time spent in calculations of symmetric matrix portrait (fulladj): 0.038899 s
Time spent in reordering of the initial matrix (reorder) : 0.719669 s
Time spent in symbolic factorization (symbfct) : 0.164026 s
Time spent in data preparations for factorization (parlist) : 0.004884 s
Time spent in copying matrix to internal data structure (A to LU): 0.000000 s
Time spent in factorization step (numfct) : 15.284947 s
Time spent in allocation of internal data structures (malloc) : 0.024751 s
Time spent in additional calculations : 0.305008 s
Total time spent : 16.542184 s
Statistics:
===========
Parallel Direct Factorization is running on 6 OpenMP
< Linear system Ax = b >
number of equations: 144657
number of non-zeros in A: 8811657
number of non-zeros in A (%): 0.042109
number of right-hand sides: 1
< Factors L and U >
number of columns for each panel: 72
number of independent subgraphs: 0
< Preprocessing with state of the art partitioning metis>
number of supernodes: 16666
size of largest supernode: 4251
number of non-zeros in L: 77945805
number of non-zeros in U: 73504188
number of non-zeros in L+U: 151449993
gflop for the numerical factorization: 1100.816559
gflop/s for the numerical factorization: 72.019651
```

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