Function periods

pub fn periods<P, F>(
    rate: f64,
    present_value: P,
    future_value: F,
    continuous_compounding: bool,
) -> f64
where
    P: Into<f64> + Copy,
    F: Into<f64> + Copy,

Returns the number of periods given a periodic rate along with the present and future values, using simple compounding.

Note that the returned number of periods will be a floating point number representing fractional periods.

See the periods module page for the formulas.

Related functions:

• To calculate the periods using simple compounding and return a struct that shows the formula and can be used to produce the the period-by-period values use periods_solution.
• To calculate the periods using continuous compounding use periods_continuous or periods_continuous_solution.

Arguments

• rate - The rate at which the investment grows or shrinks per period, expressed as a floating point number. For instance 0.05 would mean 5% growth. Often appears as r or i in formulas.
• present_value - The starting value of the investment. May appear as pv in formulas, or C for cash flow or P for principal.
• future_value - The final value of the investment.
• continuous_compounding - True for continuous compounding, false for simple compounding.

Panics

The call will fail if the rate, the present value, or the future value is infinite or not a number (NaN).

The call will also fail in any of the follwing cases because there is no number of periods that would make the calculation work:

• The periodic rate is less than -1.0.
• The present value is zero and the future value is nonzero.
• The present value is nonzero and the future value is zero, unless the rate is exactly -1.0%.
• The present value is negative and the future value is positive or vice versa.
• The present value and future value are both negative, the future value is less than the present value, and the periodic rate is zero or negative.
• The present value and future value are both negative, the future value is greater than the present value, and the periodic rate is zero or positive.
• The present value and future value are both positive, the future value is greater than the present value, and the periodic rate is zero or negative.
• The present value and future value are both positive, the future value is less than the present value, and the periodic rate is zero or positive.

Examples

use finance_solution::*;

// The interest rate is 8% per year.
let rate = 0.08;

// The starting value is $5,000.00.
let present_value = -5_000.00;

// The ending value is $7,000.00.
let future_value = 7_000.00;

let continuous_compounding = false;

// Calculate the number of years required.
let fractional_periods = periods(rate, present_value, future_value, false);
dbg!(&fractional_periods);
assert_rounded_2(4.37, fractional_periods);

// Round up to get a whole number of years.
let periods = fractional_periods.ceil() as u32;
dbg!(&periods);
assert_eq!(5, periods);