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MathGroup Archive 2009

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Two questions about modification of a matrix.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg101041] Two questions about modification of a matrix.
  • From: Mayasky <alix.zhang at gmail.com>
  • Date: Mon, 22 Jun 2009 04:22:19 -0400 (EDT)

Suppose there is a N*N matrix.

1. How can I change all elements that satisfy i*j>N to 0 ? (Here i, j
is position of this element, as in mat[[i,j]])

2. How can I change all negative elements in that matrix to 0 ?

I know a "for loop" can be used, I just wonder if there is any more
concise and beautiful ways. (I doubt Mathematica doesn't have a 'find'
function as in another system which conveniently returns indice of elements
that satisfy a certain condition)


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