Returns the effective compounded interest rate given a nominal interest rate.
nom_rate: the nominal interest rate.
num: the number of times interest is credited / compounded during the period that nom_rate applies to.
If an investment has a nominal rate, say for a year, but interest is paid and credited say each quarter, the interest paid each quarter will itself start earning interest. This increases the effective value. This function returns the effective rate - that is, the rate that would have to be paid at the end of the (say) year to give the same return.
The formula used is:
returns approximately 6.14%, which is the effective rate of an investment with a nominal rate of 6% per annum, compounded quarterly.