[SciPy-user] Sparse indexing workarounds

Bill Baxter wbaxter@gmail....
Sun Apr 8 06:23:47 CDT 2007

Does anyone have an easy (and efficient way) to update a submatrix of
a big sparse matrix?

  K = scipy.sparse.lil_matrix(bigN,bigN)
  conn = [1,4,11,12]
  K[ix_(conn,conn)] += elemK

where elemK is a 4x4 dense matrix.

This kind of thing is very commonly needed in FEM codes for assembling
the global stiffness matrix.  But sparse doesn't seem to support
either += or indexing with the open grid of indices returned by ix_.


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