Trinomial model using VBA code

The market doesn't want to go through 1.34 in order to make our Butterfly spread on EUR/USD much more profitable.

Which is the cheapest strike to get the smallest value for a straddle given a spot level and a implied volatility ?

Implied volatility derived using standard models isn't the same neither for every strike of a particular maturity. nor for different maturities.

Adding a constraint on a european style option tree is simple.

Black & Scholes option pricing model is the most known amongst traders. Here is how one could derive it.