Ambiguous expression or function input.\n The character ''x'' will be interpreted as the name of a function called ''x'' (e.g., x.m) and not as the mathematical expression ''x'' (i.e., f(x)=x). Use the anonymous function: @(x)x if you meant the mathematical expression ''x''. If FUN is a MATLAB object, it must have an feval method. FUN must be a function, a valid character vector expression, or an inline function object.