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# Source: https://gist.github.com/mattetti/1015948
module LoanCreator::ExcelFormulas
# Returns the interest payment
# for a given period for an investment based on periodic, constant payments and a constant interest rate.
def ipmt(rate, per, nper, pv, fv=0, type=0)
p = _pmt(rate, nper, pv, fv, 0);
ip = -(pv * _pow1p(rate, per - 1) * rate + p * _pow1pm1(rate, per - 1))
(type == 0) ? ip : ip / (1 + rate)
end
# Returns the payment on the principal
# for a given period for an investment based on periodic, constant payments and a constant interest rate.
def ppmt(rate, per, nper, pv, fv=0, type=0)
p = _pmt(rate, nper, pv, fv, type)
ip = ipmt(rate, per, nper, pv, fv, type)
p - ip
end
protected
def _pmt(rate, nper, pv, fv=0, type=0)
((-pv * _pvif(rate, nper) - fv ) / ((bigd('1.0') + rate * type) * _fvifa(rate, nper)))
end
def _pow1pm1(x, y)
(x <= -1) ? ((1 + x) ** y) - 1 : Math.exp(y * Math.log(bigd('1.0') + x)) - 1
end
def _pow1p(x, y)
(x.abs > bigd('0.5')) ? ((1 + x) ** y) : Math.exp(y * Math.log(bigd('1.0') + x))
end
def _pvif(rate, nper)
_pow1p(rate, nper)
end
def _fvifa(rate, nper)
(rate == 0) ? nper : _pow1pm1(rate, nper) / rate
end
end
Version data entries
16 entries across 16 versions & 1 rubygems