How do i check if the input arguments of a function is of type double?

When I tried to perform double integration it is generating an error "input arguments should be of type double". I used syms command. How do I check if the parameters of my function are of type 'double'

[Jan]

Ok, this question is closed, but why? I've started to create an answer before it was closed, but hitting the "Save" button did not succeed. Therefore I've tried it 20 times thinking that I'm a victim of the old latency problem of the forum. Afterwards I gave up and reloaded the question. But now the information that Walter has closed the thread does not really help.