out = Matched(double(im1)+1);

out = Matched(double(im1)+1);

what is happened here ?

Answer 1

[Adam Danz]

Short answer

Not enough information to know what's going on.

Longer, speculative answer

im1 is a variable, probably numeric, maybe logical.

double() is converting im1 to double precision: https://www.mathworks.com/help/matlab/ref/double.html

Then you're adding 1.

Matched is either a function or a variable. If it's a function, it's a custom function so no one can possibly know what's going on there without seeing the function. If it's a variable, then you're indexing that variable.