How do I test for integers in MATLAB?

Question

I'm writing a program that will calculate factorials of integers. However, the part I'm stuck on is if someone enters a non-integer such as 1.3, I'd like to be able to test the input and display "The number you have entered is not an integer"

Answer 1

You can use the mod function, which returns the remainder after division. All integers are divisible by 1. So a good test for non-integer would be

integerTest=~mod(value,1);

This returns 0 if value is not an integer and 1 if it is. You can then use this as a conditional to reject non-integer user inputs.

Answer 2

Here is another variation (you can see it being used in ISIND function: edit isind.m):

integerTest = ( x == floor(x) );

On my machine, it is faster than the other proposed solutions:

%# create a vector of doubles, containing integers and non-integers
x = (1:100000)';                       %'
idx = ( rand(size(x)) < 0.5 );
x(idx) = x(idx) + rand(sum(idx),1);

%# test for integers
tic, q1 = ~mod(x, 1); toc
tic, q2 = x==double(uint64(x)); toc
tic, q3 = x==floor(x); toc

%# compare results
assert( isequal(q1,q2,q3) )

Timings:

Elapsed time is 0.012253 seconds.
Elapsed time is 0.014201 seconds.
Elapsed time is 0.005665 seconds.