Monotonicity

Key Monotonicity in Interpolation refers to the numerical value for the Quantlib monotonicity parameter.
Enhances implementation of the convex monotone method as described in "Interpolation Methods for Curve Construction" by Hagan & West AMF Vol 13, No2 2006. Web reference available here
A setting of monotonicity = 1 and quadraticity = 0 will reproduce the basic Hagan/West method. However, this can produce excessive gradients which can mean P&L swings for some curves.
Setting monotonicity < 1 and/or quadraticity > 0 produces smoother curves.
Extra enhancement to avoid negative values (if required) is available through the Force Pos entry.