"Impossible weights"

This checklist is for when nonlinear regression reports "Impossible weights" at the top of the results. View other checklists if your curve fit ended with a different completion code: Completed, Bad initial values, Interrupted, Not converged, ambiguous, Hit constraint, Don't fit, Too few points, or Perfect fit.

Prism reports "Impossible weighting" when weighting would lead to division by zero for one or more point. This can happen when you choose to weight by the reciprocal of Y, and the Y value of the curve equals zero at some X values. Since division by zero is impossible, Prism reports "Impossible weighting". Go to the weights tab and choose a different weighting method.