Matlab and any, difficulties in understanding

Question

I can't understand what this code does:

if any(scale==0)
   loglik = -inf;

I have to translate it into C++ with the Armadillo library, that does not have an any function so I was wondering how to do it.

I've read the matlab manuals, but it is still confusing. I've then tried with this test case:

if any([*]==0)
   1
else
   0
end

using as * those values (and many more):

[0 0;0 0]
[1 0;0 0]
[1 0;1 0]
[1 0;0 1]
[1 1;1 1]

but I am still confused and results are dark.. any explanation please?

Answer 1

Matlab (and Armadillo) represent booleans as 0 for false and 1 (or really anything that's not 0) for true. They both define an == operator over matrices/vectors that does component-wise comparisons and outputs a matrix of booleans. any is taking in that matrix of booleans and checking if any are non-zero.

Armadillo does not appear to have any, but it does provide find which can be used to implement any:

!find(X, 1).is_empty()

is equivalent (albeit possibly slower): it constructs a vector of at most one non-zero elements (documentation for find). If it's empty, then there are no non-zero elements, so any would return false.

Answer 2

As of version 3.910, Armadillo has the any() function.