def pvannuity(rate, npmts, amt=<NUM_LIT:1.>):
return amt * (<NUM_LIT:1.> - (<NUM_LIT:1.> + rate)**-npmts) / rate<EOL>
Present value of `n` payments of a given size given
an interest rate per payment interval of `rate`.

.. versionchanged:: 0.3.0
   `amt` can be specified in function call.

Parameters
----------
rate : float
    Interest rate per payment period. Note that if
    payments are monthly and known interest rate is annual,
    `rate` must be calculated as effective *monthly* interest.
npmts : int
    Number of payments.
amt : float, optional
    Amount of each payment. Defaults to 1.