rig {mgcv} | R Documentation

## Generate inverse Gaussian random deviates

### Description

Generates inverse Gaussian random deviates.

### Usage

    rig(n,mean,scale)

### Arguments

`n` | the number of deviates required. If this has length > 1 then the length is taken as the number of deviates required.
`mean` | vector of mean values.
`scale` | vector of scale parameter values (lambda, see below)

### Details

If x if the returned vector, then E(x) = `mean` while var(x) = `scale*mean^3`. For density and distribution functions see the `statmod` package. The algorithm used is Algorithm 5.7 of Gentle (2003), based on Michael et al. (1976). Note that `scale` here is the scale parameter in the GLM sense, which is the reciprocal of the usual ‘lambda’ parameter.

### Value

A vector of inverse Gaussian random deviates.

### Author(s)

Simon N. Wood simon.wood@r-project.org

### References

Gentle, J.E. (2003) Random Number Generation and Monte Carlo Methods (2nd ed.) Springer.

Michael, J.R., W.R. Schucany & R.W. Hass (1976) Generating random variates using transformations with multiple roots. The American Statistician 30, 88-90.

http://www.maths.bris.ac.uk/~sw15190/

### Examples

    require(mgcv)
    set.seed(7)
    ## An inverse.gaussian GAM example, by modify `gamSim' output...
    dat <- gamSim(1,n=400,dist="normal",scale=1)
    dat$f <- dat$f/4 ## true linear predictor
    Ey <- exp(dat$f);scale <- .5 ## mean and GLM scale parameter
    ## simulate inverse Gaussian response...
    dat$y <- rig(Ey,mean=Ey,scale=.2)
    big <- gam(y~ s(x0)+ s(x1)+s(x2)+s(x3),family=inverse.gaussian(link=log),
              data=dat,method="REML")
    plot(big,pages=1)
    gam.check(big)
    summary(big)

[Package mgcv version 1.8-12 Index]