# 4.5: Indexing Errors

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An index can be any kind of expression, but the value of the expression has to be a positive integer, and it has to be less than or equal to the length of the vector. If it’s zero or negative, you’ll get an error:

>> Y(0)
Array indices must be positive integers or logical values.

If it’s not an integer, you get an error:

>> Y(1.5)
Array indices must be positive integers or logical values.

If the index is too big, you also get an error:

>> Y(5)
Index exceeds the number of array elements (4).

The error messages use the word array rather than matrix, but they mean the same thing, at least for now.

This page titled 4.5: Indexing Errors is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.