problem looping through arrays

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user343423
user343423 2021-11-17
编辑： the cyclist 2021-11-17
This is the question: Let M be a matrix of positive integers. Write a function with header [Q] =myTrigOddEven(M), where Q(i ,j ) = sin (M(i,j)) if M (i , j ) is even, and Q(i ,j ) =cos (M (i , j )) if M (i , j ) is odd.
This is the function I came up with:
function [Q] = myTrigOddEven(M)
for i = 1:(length(M)-1)
for j = 1:(length(M)-1)
if mod(Q(i,j),2) == 0
Q(i,j) = sin (M (i , j ));
else
Q(i,j) = cos (M (i , j ));
end
end
end
end
I'm getting an error with the statement in the if and the else. At the parts Q(i,j) = sin (M (i , j )); and Q(i,j) = cos (M (i , j ));, it says that Q changes size on every loop interation, and I'm not sure how to fix that.

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回答（1 个）

the cyclist
the cyclist 2021-11-17
编辑：the cyclist 2021-11-17
I think you intended
if mod(M(i,j),2) == 0
rather than
if mod(Q(i,j),2) == 0
Regarding the warning about Q changing size, you want to preallocate that array. For example, you could put
Q = zeros(size(M));
at the beginning of the function.
You can read about why preallocation is important in this documentation.

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