memory allocation

[li pan]

Dear developers,
last week I asked a question about memory allocation.
I'm trying to comprehend it from another aspect. The
question is, if I have a mesh (HEX8) of size 128 x 128
x 40. There are three components for each node. In
case of displacement, it's (u,v,w). So there must be
128 x 128 x 40 x 3 = 1966080 degrees of freedom. In
sparse pattern, each element must have 7 x 3 = 21
non-zeros, because each node has 6 neighbours, plus
itself, it's 7 nodes, then multiply 3 components, we
get 21. If everything is allright until now, we have
1966080 x 21 non-zeros in the system matrix. This
corresponds 42 MB. I wonder why there was so much
memory required by petsc, more than 2 GB.
Probably, I'm wrong on some points. Please remind me.

kind regards

pan




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