I am performing a finite-precision operation on a matrix A which I know precisely; call the result B. The operation is taking the square root by B = MatrixPower[A,1/2], but it's not quite relevant. The point is that the form of A is such that the output will contain a lot of entries equal to 0, simply because A has a lot of invariant subspaces spanned by the standard base vectors.

I would like to see resulting matrix is like: in the first approximation it interests me how many non-zero entries it has and where. The problem is, the entries of B which are supposed to be 0 come out as small reals of the type $1.234...\times 10^{-10}$. I've tried applying N to B with some modest requirement on precision, but this does not seem to help. Ideally, I would like to set all entries of B which are approximately 0 to precisely 0. Any help would be appreciated.

P.S. It just occurred to me that I can take a function f that maps small numbers to 0, and is identity otherwise, and apply it to B element-wise. But there should be a more elegant solution, it seems to me.

  • $\begingroup$ Take a look at Chop. $\endgroup$ – Kuba Jun 23 '13 at 13:26
  • $\begingroup$ @Kuba: Precisely what I needed! Thanks. $\endgroup$ – Jakub Konieczny Jun 23 '13 at 13:28
  • $\begingroup$ This question has already been answered here. $\endgroup$ – m_goldberg Jun 23 '13 at 13:38

Perhaps you will find Chop useful.

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  • $\begingroup$ Chop is just what I was looking for. Thank you! $\endgroup$ – Jakub Konieczny Jun 23 '13 at 13:29

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