error using trap membership function

Error using coder.internal.assert (line 33)

Third parameter must be less than or equal to fourth parameter.

Error in coder.internal.errorIf (line 7)

coder.internal.assert(~cond, msgID, varargin{:});

Error in fuzzy.internal.utility.validateTrapMFParameterValues (line 15)

coder.internal.errorIf(params(3) > params(4), ...

Error in trapmf (line 25)

fuzzy.internal.utility.validateTrapMFParameterValues(params)

Error in fuzzyEnt (line 14)

U=trapmf(1:256,x(i:i+3));