Any hint about this error?

Steps to reproduce (on Matlab R2013a 64bit Win machine):

R = rand(7,7);

>> ind_diag = eye(7);

>> R(ind_diag)

Error: Subscript indices must either be real positive integers or logicals.

>> ind_diag = ~~eye(7);

>> R(ind_diag)

ans =

    0.8702
    0.3818
    0.6567
    0.1098
    0.4873
    0.1401
    0.7657

Cheers, Chris

[Jos (10584)]

logical(x) is faster, and easier to read!, than ~~x

Answer 1

[Chris]

thank you Harjeet,

however i still wonder why eye() or ones() don't work.

Is it a bug or a misuse of these functions?

[Jos (10584)]

Take a look at this

a = 1
b  = logical(a)
class (a)
class(b)

[Chris]

thanks!

Answer 2

[harjeet singh]

use this

R = rand(7,7);
ind_diag = logical(eye(7));
R(ind_diag)

Answer 3

[harjeet singh]

eye() will give you a output in double format and when you use ~~eye() it automatically converts in logical.

the command R(ind_diag) uses inputs as logical so that's why you have to convert it into logical before use

[Chris]

thank you harjeet