gigCheckPars function

Check Parameters of the Generalized Inverse Gaussian Distribution

Given a putative set of parameters for the generalized inverse Gaussian distribution, the functions checks if they are in the correct range, and if they correspond to the boundary cases.

gigCheckPars(Theta, ...)

Arguments

• Theta: Numeric. Putative parameter values for a generalized inverse Gaussian distribution.
• ...: Further arguments for calls to all.equal.

Details

The vector Theta takes the form c(lambda,chi,psi).

If either chi or psi is negative, an error is returned.

If chi is 0 (to within tolerance allowed by all.equal) then psi and lambda must be positive or an error is returned. If these conditions are satisfied, the distribution is identified as a gamma distribution.

If psi is 0 (to within tolerance allowed by all.equal) then chi must be positive and lambda must be negative or an error is returned. If these conditions are satisfied, the distribution is identified as an inverse gamma distribution.

If both chi and psi are positive, then the distribution is identified as a normal generalized inverse Gaussian distribution.

Returns

A list with components: - case: Whichever of 'error', 'gamma', invgamma, or 'normal' is identified by the function.

• errMessage: An appropriate error message if an error was found, the empty string "" otherwise.

References

Paolella, Marc S. (2007) Intermediate Probability: A Computational Approach, Chichester: Wiley

Author(s)

David Scott d.scott@auckland.ac.nz

See Also

dgig

Examples

gigCheckPars(c(-0.5,5,2.5))      # normal
gigCheckPars(c(0.5,-5,2.5))      # error
gigCheckPars(c(0.5,5,-2.5))      # error
gigCheckPars(c(0.5,-5,-2.5))     # error
gigCheckPars(c(0.5,0,2.5))       # gamma
gigCheckPars(c(-0.5,0,2.5))      # error
gigCheckPars(c(0.5,0,0))         # error
gigCheckPars(c(-0.5,0,0))        # error
gigCheckPars(c(0.5,5,0))         # error
gigCheckPars(c(-0.5,5,0))        # invgamma