Extracting matrix diagonal with diag(A)

A simple function that used to run now gives an error message. What am I doing wrong?

>> a = eye(4,4);
>> diag(a)
Subscript indices must either be real positive integers or logicals.

>>

Answer 1

[Evan]

Does this fix your problem?

a = eye(4,4) == 1;
diag(a)

While the diag function works fine, if you have a variable named diag (not a good idea--give it a unique name that isn't the same as a builtin function), it expects a logical, not double, input for indexing.

[Irina]

Thank you, that's exactly what happened.

Answer 2

[Erik S.]

Do you have another matrix in your workspace called diag?

[Irina]

Thank you, that's exactly what happened.