Calculate survival probability
Source:R/calc_pd_change_overall.R
calc_survival_probability_merton.RdFunction calculates survival probability for a maturity based on a structural
Merton model.
For details on implementation please compare CreditRisk::Merton().
Unlike CreditRisk::Merton() this implementation:
only holds functionality to calculate probability of survival
can be called in vectorised fashion
additionally checks that all input values are of the same length
additionally checks input vectors for implausible values (
rmust be => 0 and all other args > 0)