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I'm currently coding a Finite Element Method (FEM) program in Mathematica. For the so called stiffness matrix I need a very large table preferably around the size of 10^6 x 10^6 cells that are all zero at first.

For a smaller Table 10^4 x 10^4, I used the following code:

Timing[k=Table[0, {i, 1, 10^4}, {j, 1, 10^4}];]

and got results around 0.9 - 1.0 seconds

since ((10^6)^2)/((10^4)^2) = 10^4 I would expect a computing time of roughly 10000 seconds (~2.7 hours) for a 10^6 x 10^6 table which is frankly put, too slow.

I tried ParallelTable as well, but it's only like 30% faster

Is there a faster way to generate such a big array?

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  • $\begingroup$ k = ConstantArray[0, {10^6, 10^6}, SparseArray] $\endgroup$
    – Coolwater
    Jul 3, 2018 at 9:35
  • $\begingroup$ .. or k = SparseArray[{}, {10^6, 10^6}]? $\endgroup$
    – kglr
    Jul 3, 2018 at 9:43
  • $\begingroup$ @Coolwater, kglr exactly what I was looking for, thanks! $\endgroup$
    – p4di
    Jul 3, 2018 at 10:46

1 Answer 1

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As Coolwater and kglr have commented SparseArray was exactly what I was looking for!

k = ConstantArray[0, {10^6, 10^6}, SparseArray]

k = SparseArray[{}, {10^6, 10^6}]

both do the job.

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