Why matlab shows an error like >> Undefined function or variable 'refConst'.? as I used the loop before the error line .. Switch M case 8 % 256QAM refConst = qammod((0:255).', 256,'UnitAveragePower', true); end?

Matlab shows an error in the line>> ConstDiagRx=comm.ConstellationDiagram('showReferenceConstellation',... true,'ReferenceConstellattion',refConst,'positon',figposition([20 15 30 40]),... 'EnableMeasurements',true,'MeasurementInterval',length(dataSymbols),... 'Title F-OFDM Demolated Symbols','Name','F-OFDM Reception',... 'XLimits',[-1.5 1.5],'YLimits',[-1.5 1.5]); here I have used the Matlab version R2015a