Dakota Reference Manual
Version 6.4
LargeScale Engineering Optimization and Uncertainty Analysis

Aleatory uncertain variable  gamma
This keyword is related to the topics:
Alias: none
Argument(s): INTEGER
Default: no gamma uncertain variables
Required/Optional  Description of Group  Dakota Keyword  Dakota Keyword Description  

Required  alphas  First parameter of the gamma distribution  
Required  betas  Second parameter of the gamma distribution  
Optional  initial_point  Initial values  
Optional  descriptors  Labels for the variables 
The gamma distribution is sometimes used to model time to complete a task, such as a repair or service task. It is a very flexible distribution with its shape governed by alpha and beta.
The density function for the gamma distribution is given by:
where and . Note that the exponential distribution is a special case of this distribution for parameter .
When used with design of experiments and multidimensional parameter studies, distribution bounds are inferred. These bounds are [0, ].
For vector and centered parameter studies, an inferred initial starting point is needed for the uncertain variables. These variables are initialized to their means for these studies.