Closed form approximations to the fundamental solution of parabolic PDEs is considered. The approach consists on approximations based on a parametrix series expansion. The approximation error can be bounded by a gaussian function and it is of an order of t^2. These explicit expressions have...

Exceptional accuracy and speed for option pricing are available via quadrature (Andricopoulos, Widdicks, Duck, and Newton, 2003), extending into multiple dimensions with complex path-dependency and early exercise (Andricopoulos, Widdicks, Newton, and Duck, 2007). However, the exposition is...