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Re: Trying to avoid loops when adjusting two variables.

From: Carlo de Falco
Subject: Re: Trying to avoid loops when adjusting two variables.
Date: Tue, 17 Apr 2007 15:06:04 +0200

On 4/17/07, Harbinson, Jeremy <address@hidden> wrote:
This is one of those how-do-I-avoid loops questions.

Simple case of one variable in a function:

if I have a vector (A) and a function (eg y=2*x^2) I can easily apply the
function to the vector without looping as follows

and I get an output in which the function has been applied sequentially to
every element of the input vector.

More complicated case (the one for which I would like to avoid a for loop):

I now have 2 vectors A and B and a function with two variables (eg y=z*x^2).
I want to apply the function to both A and B, using B for variable z and A
for variable x, and get an output which is a grid within which each element
is the result of applying the function to a particular pair of elements from
A and B. At the moment the only way I can think of doing this is to use a
loop in which I first calculate B(1).*A.^2, then calculate B(2).*A.^2 etc
until I have cycled through every element in B. Can this procedure be
vectorised or is looping over one of the variables the only solution?

Jeremy Harbinson

I would do:

A = [1:10];
B = [5:2:20];
x = A(ones(length(B),1),:);
z = B'(:,ones(length(A),1));


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