Manuals/calci/GAMMAINV

GAMMAINV(prob,alpha,beta)

• $prob$ is the probability value associated with gamma distribution
• $alpha(\alpha )$ & $beta(\beta )$ are the values of the shape and rate parameters

Description

• This function gives the inverse value of Cumulative Gamma Probability Distribution.
• This distribution is the Continuous Probability Distribution on the positive real line and it is of the reciprocal of a variable distributed according to the gamma distribution with two parameters $\alpha$ & $\beta$.
• It is used in Bayesian statistics.
• In $GAMMAINV(prob,\alpha ,\beta )$ , $prob$ is the probability value associated with Gamma Distribution,$\alpha$ is called shape parameter and $beta$ is the rate parameter of the distribution.
• If $GAMMADIST(x,alpha,beta,TRUE)=prob$, then $GAMMAINV(prob,alpha,beta,)=x$.
• GAMMAINV use the iterating method to find the value of $x$.
• Suppose the iteration has not converged after 100 searches, then the function gives the error result.
• This function will give the error result when

1.Any one of the arguments are non-numeric
2.$\alpha \leq 0$ or $\beta \leq 0$
3.$prob<0$ or $prob>1$

Examples

1. =GAMMAINV(0.65189,2,5) = 11.1335534510
2. =GAMMAINV(0.006867292,5,7) = 8.155481331
3. =GAMMAINV(0.1543869,9,3) = 18.0467153645
4. =GAMMAINV(1,9,3) = 82.51739521528073
5. =GAMMAINV(1.1,9,3) = NAN, because $prob>1$

See Also

• GAMMADIST
• GAMMALN

References

Gamma Distribution