Why can't Matlab do the factorial of a non-integer number?

27 vues (au cours des 30 derniers jours)
HWIK
HWIK le 6 Fév 2022
Commenté : Dyuman Joshi le 23 Jan 2024
Hi,
I tried using the factorial function on a number with decimals and got the following error: N must be an array of real non-negative integers.
Is there an alternative so that it can calculate the factorial of a number with decimals like Excel does?
Thanks for your time

Réponse acceptée

Davide Masiello
Davide Masiello le 6 Fév 2022
Modifié(e) : Davide Masiello le 6 Fév 2022
MatLab 'factorial' is coded so to work with integers only.
The generalization of a factorial is the Γ function, which is
and the relation with the factorial is
MatLab implements the Γ function. Therefore, to compute the factorial of 1.5 you can write
gamma(2.5)
Which yields 1.3293, the correct answer.
  2 commentaires
Andy
Andy le 23 Jan 2024
Modifié(e) : Andy le 23 Jan 2024
Would you know how to calculate the inverse gamma function in Matlab?
f(1.3293) = 2.5.
I tried gaminv(1.3293) but it doesn't seem related. Same with gammaincinv.
I'm trying to find a real number whose factorial is equal to a number that I input.
Dyuman Joshi
Dyuman Joshi le 23 Jan 2024
There is no function in MATLAB, in-built or a part of the toolbox, that offers that functionality directly.
(Possibly because) There is no known explicit relation or definition which can be utilized to obtain that.
However, you can try this -
%value of which the inverse is to be calculated
y = gamma(2.5)
y = 1.3293
f = @(x, val) gamma(x) - val;
out = fzero(@(x) f(x, y), 2)
out = 2.5000
But note that the inverse gamma function is not one-on-one (reference - Graph of the function provided in its wikipedia article - https://en.wikipedia.org/wiki/Inverse_gamma_function), so multiple solutions exist for each input.
The value obtained as the output depends on the initial guess -
%Finding the inverse for the same, but with initial guess as 1
fzero(@(x) f(x, y), 1)
ans = 0.6809

Connectez-vous pour commenter.

Plus de réponses (2)

David Hill
David Hill le 6 Fév 2022
Use the gamma function.
gamma(1.3);

DGM
DGM le 6 Fév 2022
See the Gamma function
Or in MATLAB, gamma().
Note that if you're trying to replicate the behavior of factorial, the input is offset by 1:
factorial([2 3 4])
ans = 1×3
2 6 24
gamma([2 2.5 3 3.2 3.6 4])
ans = 1×6
1.0000 1.3293 2.0000 2.4240 3.7170 6.0000
gamma([2 2.5 3 3.2 3.6 4]+1) % offset by 1
ans = 1×6
2.0000 3.3234 6.0000 7.7567 13.3813 24.0000

Catégories

En savoir plus sur Gamma Functions dans Help Center et File Exchange

Produits


Version

R2021b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by