In MATLAB,

The factorial n! of a positive integer is defined by n!=n*(n-1)*(n-2)*3*2*1, where 0!=1. Write a user-defined function that calculates the factorial n! of a number. For function name and arguments, use y=fact(x), where the input argument x is the number whose factorial is to be calculated and the output argument y is the value x!. The function displays an error message if a negative or non-integer number is entered when the function is called. Do not use the MATLAB built-in function factorial.