My eps are all real positive integers and my Phi_1 values are positive values to the smallest is 3*10^(-4). Does this not count?
3*10^(-4) definitely does not count as a positive integer (because it is not an integer). However, the error you are getting has nothing to do with the values of eps or Pi_1. It has to do with xs. In this line,
ffunc is a matrix, not function, and so xs are expected to be indices (positive integers), not function inputs.