principalPayment¶

Evaluates the payment on the principal for a specified period.

Synopsis¶

principalPayment (rate, period, nPeriods, presentValue, futureValue, when)

Required Arguments¶

float rate (Input): Interest rate.
int period (Input): Payment period.
int nPeriods (Input): Total number of periods.
float presentValue (Input): The current value of a stream of future payments, after discounting the payments using some interest rate.
float futureValue (Input): The value, at some time in the future, of a current amount and a stream of payments.
int when (Input): Time in each period when the payment is made, either AT_END_OF_PERIOD or AT_BEGINNING_OF_PERIOD. For a more detailed discussion on when see the Usage Notes section of this chapter.

Return Value¶

The payment on the principal for a given period. If no result can be computed, NaN is returned.

Description¶

Function principalPayment computes the payment on the principal for a given period.

It is computed using the following:

\[\mathit{payment}_i - \mathit{interest}_i\]

where $payment_i$ is computed from payment for the i-th period, $interest_i$ is calculated from interestPayment for the i-th period.

Example¶

In this example, principalPayment computes the principal paid for the first year on a 30-year $100,000 loan with an annual interest rate of 8%. The payment is made at the end of each year.

from __future__ import print_function
from numpy import *
from pyimsl.math.principalPayment import principalPayment, AT_END_OF_PERIOD

rate = 0.08
period = 1
n_periods = 30
present_value = 100000.00
future_value = 0.0
when = AT_END_OF_PERIOD

principal = principalPayment(rate, period, n_periods,
                             present_value, future_value, when)
print("The payment on the principal for the first year of ")
print("the $100,000 loan is $%.2f." % (principal))

Output¶

The payment on the principal for the first year of 
the $100,000 loan is $-882.74.