MATLAB: Are the Lagrange multipliers (lambda), that are returned by CONSTR for equality constraints, always positive

bugconstrfminconlagrangemultipliersr14

Why are the Lagrange multipliers (lambda), that are returned by CONSTR for equality constraints, always positive?

Best Answer

This bug has been fixed for Release 14 (R14). For previous releases, please read below for any possible workarounds:
There isn't a clearly defined convention for dealing with the signs of Lagrange multipliers with CONSTR when dealing with equality constraints. The code in CONSTR only returns the absolute value since this is what's used by the algorithm to determine if a solution has been found.
We are considering enhancing the code to return positive and negative values when appropriate. We currently do not have a timeframe for when this will be implemented.