Help with Function using Logical Indexing

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RG
RG 2015-5-11
回答： Guillaume 2015-5-11
Hi, I'm trying to write a function, without using loops, which takes a matrix A and an integer k as inputs and returns a matrix B with same size as A. Elements of B are divisible by k. If an element of A is divisible by k, then the corresponding element in B has the same value. If an element of A is not divisible by k, then the corresponding element of B must be the product of the given element of A and k. For example, the call ([1 2 ; 3 4], 2) would return [2 2 ; 6 4]. I know that it is possible using logical indexing, but couldn't put it all together. Any help would be appreciated.

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Guillaume
Guillaume 2015-5-11
You've nearly got it. You don't want to contenate the results of the logical operations you've done. You want to replace the elements of a matrix according to the logical indexing.
I don't want to give you the full solution as it's homework, instead here are the steps I would follow:
  1. copy A into B
  2. create a logical array showing which elements of A are not divisible by k (your mod(A,k)~=0)
  3. Use the logical array to replace those elements of B that are not divisible by k by the same elements multiplied by k. You should have the logical array on both side of the =
That's all. You could have step 2 and 3 on the same line.

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