Is the implied volatility in QuantLib independent of the pricing engine?

Question

This might be a stupid question as I just started looking into QuantLib. (I'm using the python API.) It seems that the implied volatility calculation does not require a pricing engine. If so, which pricing engine is used? I am interested in the implied volatility of American options.

Answer 1

The problem here is that the option cannot reuse the same engine set to the instrument. This is because it needs to create a new engine, in which the volatility is flat and under the control of the method (since it needs to be changed by the solver). This can't be done in a generic way, especially considering that users might implement entirely new engines.

All the method can do is return an estimate based on one chosen engine. The default chosen is FdBlackScholesVanillaEngine with default parameters. If you want to use a different engine, or the same engine with different parameters, you'll have to duplicate the code inside the method.