variance_cumulation_from_vols: Create a variance cumulation function from a volatility term structure
Description
Given a volatility term structure, create a corresponding variance
cumulation function. The function assumes piecewise constant
forward volatility, with the final such forward volatility
extending to infinity.
Usage
variance_cumulation_from_vols(vols_df)
Arguments
vols_df
A data.frame with numeric columns time (in
increasing order) and volatility (not decreasing so quickly
as to give negative forward variance)
Value
A function taking two time arguments, which returns the cumulated
variance from the second to the first