Using an empty matrix as an Index

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Whitney
Whitney on 6 Dec 2012
I can't find any documentation about this so I don't understand why matlab doesn't consider using an empty matrix as an index an error worthy event.
x = [3,4];
y = find(x = 0); % returns an empty matrix
i(y) = 0; % returns i = []
Is there a reason for this? It took me quite a while to realize this was causing problems in my program and when I did discover the behavior, I had a momentary thought that I was using perl instead of matlab.

Answers (2)

Sean de Wolski
Sean de Wolski on 6 Dec 2012
What do you expect it to return? If it's not being indexed by anything then it shouldn't extract anything. Perhaps this will look slightly better:
X = magic(5)
X(2:1,:)
  2 Comments
Jan
Jan on 7 Dec 2012
Exactly. The posted code does this:
Create a variable "i", which have all elements of the index vector set to 0. If the index vector is empty, "i" must be empty also.

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Pritesh Shah
Pritesh Shah on 7 Dec 2012
x = [3,4]; y = find(x = 0); % returns an empty matrix i(y) = 0; It should be == instead of = y = find(x == 0); % returns an empty matrix
Now, it will work... Enjoy !!

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