I would like to create a function that takes a numerical value and has a default value. For instance, I can define
f[x_:10] := 2 * x
And this works. If I would like to check whether the x is a numeric value, I can write this as
f[x_?NumericQ] = 2 * x
But if I try to do both, that is check whether it is numeric and it has default value, the function does not work. In other words, the following expression is not correct
f[x_?NumericQ:10] := 2 * x
What should be the correct syntax in such case?
