I am getting wrong answer for factorial(22)

I keep getting 1.1198e+21 for factorial(22) but in the xample problem on matlab the answer is 1.24000728E21.

Problem

a1 = factorial(22)

b = (sqrt(2*pi*22))*(22^22/exp(22))

c = (abs((a1 - b)/a1))*100

Outputs

a1 = 1.1198e+21

b = 1.1198e+21

c = 0

Answer 1

[James Tursa]

R2016a PCWIN64:

>> a1 = factorial(22)
a1 =
     1.124000727777608e+21
>> b = (sqrt(2*pi*22))*(22^22/exp(22))
b =
     1.119751494628234e+21
>> c = (abs((a1 - b)/a1))*100
c =
   0.378045409078625

What version of MATLAB are you running? Are you shadowing the MATLAB factorial( ) function with one of your own? I.e., what does this reply:

   which factorial

[Liam Sullivan]

Oh now it's giving me the correct answer. I am not sure what was wrong with it so i exited it out, reopened it and then ran the script again. Thanks though!

[Steven Lord]

If the problem recurs, run the last line of code in James Tursa's answer and check that you're calling the factorial function included in MATLAB. Actually, I'd suggest a slight modification to James's code:

which -all factorial

The factorial.m in the toolbox\matlab\specfun directory is the factorial function included in MATLAB so it's OK. Any factorial.m files listed in the output of the above command whose entry ends with "<some class name> method" are OK as well. If you see other factorial.m files you may want to rename or remove them.