Fitting Data with user defined function

ROOT
16 
"crystalball" = "[Constant] * ROOT::Math::crystalball_function(x, [Alpha], [N], [Sigma], [Mean])"

Wikipedia → Crystal Ball function ;

ROOT::Math::crystalball_function ;

${ROOTSYS}/tutorials/math/CrystalBall.C ;
${ROOTSYS}/tutorials/fit/fitNormSum.C ;
${ROOTSYS}/tutorials/fit/fitNormSum.py