Returns the NPV (Net Present Value) of a cash flow series.
| Parameters : | rate : scalar 
 values : array_like, shape(M, ) 
  | 
|---|---|
| Returns : | out : float 
  | 
Notes
Returns the result of: [G51]

References
| [G51] | (1, 2) L. J. Gitman, “Principles of Managerial Finance, Brief,” 3rd ed., Addison-Wesley, 2003, pg. 346. | 
Examples
>>> np.npv(0.281,[-100, 39, 59, 55, 20])
-0.0066187288356340801
(Compare with the Example given for numpy.lib.financial.irr)