I'm working on a largeish system of differential equations where I encounter the
NDSolve::ndsz step size is effectively zero; singularity or stiff system suspected error.
Since this error arises from the complexity of the system I'm not able to distill a minimum example, but there might still be some useful general information we can share.
In particular I'd like to know:
What's the difference between stiffness and a singularity? How can I tell whether my sysetm is singular or stiff?
What quantity is Mathematica calculating to decide if the system is stiff/singular? Can I calculate this quantity myself to see what property of my system is causing problems?