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[Question #151130]: Efficient way to create identity matrix

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From: "yangbo@xxxxxxxxxxxx" <question151130@xxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 30 Mar 2011 23:28:24 -0000
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New question #151130 on DOLFIN:
https://answers.launchpad.net/dolfin/+question/151130

Hi, --- This might be stupid. Just wondering if there is some efficient routine to create the identity matrix of a given size? The straight-forward commands I tried:

A = Matrix(n, n)
A[0,0] = 0
A.ident_zeros()

proved to be slow when n is large (e.g. time = 7sec when n = 10000). The alternative code

mesh = UnitInterval(n)
V = FunctionSpace(mesh, 'DG', 0)
f = TrialFunction(V)
g = TestFunction(V)
A = assemble( f * g * dx )
A *= n

works with less time (t = 0.05sec when n = 10000). I guess I might missed some simple routine. Anyone knows what the better way is? Thanks. --- Bo

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