[R] Applying a function to a matrix using indexes as arguments

Jeff Newmiller jdnewmil at dcn.davis.ca.us
Thu Dec 17 01:36:16 CET 2015

This calculation divides by values centered around zero.  The only context that I can think of that would require such silliness is a homework problem, and this list has a no-homework policy. If not, then mentioning the theory you are applying might help someone point you at an existing function that achieves your goals while avoiding divide-by-zero errors. 

Since you also posted in HTML I gather that you have not read the Posting Guide mentioned below.  Avoiding HTML on this list is to your benefit,  since using it inevitably leads to others seeing a garbled version of what you sent. Please read the PG for more important guidance. 
Sent from my phone. Please excuse my brevity.

On December 16, 2015 4:18:56 PM PST, Matteo Richiardi <matteo.richiardi at gmail.com> wrote:
>I have to evolve each element of a matrix W
>W <- matrix(0,2,3)
>according to some function which uses the indices of the matrix [i,j]
>w.fun = function(i,j) {
>  return A[i]*B[j]/(C[i,j])
>C <- matrix( rnorm(6,mean=0,sd=1), 2, 3)
>How can I do it, without recurring to a loop? Also, in my application I
>need to pass the function another argument.
>Thanks a lot for your suggestions.
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>and provide commented, minimal, self-contained, reproducible code.

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