April 11th, 2016, 1:18 pm
Notation: random variables in caps. Dummy args/realizations in small-caseThis is std. change-of-variable for a density. Given a density (say lognormal) [$]p_{S_T}(s)[$], what is the density [$]p_X(x)[$] of [$]X \equiv f(S_T)[$]? Work it out.Suppose [$]p_{S_T}(s)[$] is lognormal with a peak at 110, and [$]f(s) = \max(s-100,0)[$]. Then, you are going to find that [$]p_X(x)[$] looksroughly lognormal to the right of [$]x=0[$] with a peak at 10, plus it has a Dirac mass at 0. Perhaps these are your two peaks. For simple barriers,similar ideas apply; you will get smooth densities that end in Dirac masses where the barriers kick in. =================================================================================================p.s. Definitely student forum. If this all seems confusing, practice with this. Suppose [$]p_X(x)[$] is a Gaussian. Then what is the density of [$]Y = f(X) = X^2[$]? What is the transformation rule for general [$]y = f(x)[$]?
Last edited by
Alan on April 10th, 2016, 10:00 pm, edited 1 time in total.