Compute the future value.
Parameters:  rate : scalar or array_like of shape(M, )
nper : scalar or array_like of shape(M, )
pmt : scalar or array_like of shape(M, )
pv : scalar or array_like of shape(M, )
when : {{‘begin’, 1}, {‘end’, 0}}, {string, int}, optional


Returns:  out : ndarray

Notes
The future value is computed by solving the equation:
fv +
pv*(1+rate)**nper +
pmt*(1 + rate*when)/rate*((1 + rate)**nper  1) == 0
or, when rate == 0:
fv + pv + pmt * nper == 0
Examples
What is the future value after 10 years of saving $100 now, with an additional monthly savings of $100. Assume the interest rate is 5% (annually) compounded monthly?
>>> np.fv(0.05/12, 10*12, 100, 100)
15692.928894335748
By convention, the negative sign represents cash flow out (i.e. money not available today). Thus, saving $100 a month at 5% annual interest leads to $15,692.93 available to spend in 10 years.
If any input is array_like, returns an array of equal shape. Let’s compare different interest rates from the example above.
>>> a = np.array((0.05, 0.06, 0.07))/12
>>> np.fv(a, 10*12, 100, 100)
array([ 15692.92889434, 16569.87435405, 17509.44688102])