"""
Exercise 7.11 from "A primer on...
Extend the function class from 7.1 with
special methods.
"""

import numpy as np

class F:
    def __init__(self, a, w):
        self.a = a
        self.w = w

    def __call__(self, x):
        return np.exp(-self.a * x) * np.sin(self.w * x)

    def __str__(self):
        return 'exp(-a*x)*sin(w*x)'

f = F(a=1.0, w=0.1)
print(f(x=np.pi))
#0.013353835137
print(f)