The error is that you are not calling the function with enough arguments. For example, if you call you function feature_vec like this:
feature_vec(a,b)
where a and b are variables within your code
but the feature_vec is defined like this:
feature_vec(x,y,z)
it expects at least 3 input arguments, and when you call it with just two, it returns the error you receive. Take a look at the definition of your feature_vec function and make sure you use it properly.
