goffset {VGAM} | R Documentation |
GAITD Offset for the GTE Method
Description
Utility function to create a matrix of log-offset values, to help facilitate the Generally-Truncated-Expansion method
Usage
goffset(mux, n,
a.mix = NULL, i.mix = NULL, d.mix = NULL,
a.mlm = NULL, i.mlm = NULL, d.mlm = NULL, par1or2 = 1)
Arguments
mux |
Multiplier. Usually a small positive integer. Must be positive. The value 1 means no change. |
n |
Number of rows. A positive integer, it should be the number of rows of the data frame containing the data. |
a.mix , i.mix , d.mix |
See, e.g., |
a.mlm , i.mlm , d.mlm |
See, e.g., |
par1or2 |
Number of parameters of the parent distribution.
Set |
Details
This function is intended to make the
Generally-Truncated-Expansion (GTE) method
easier for the user.
It only makes sense if the linear predictors(s) are
log of the mean of the parent distribution,
which is the usual case for
gaitdpoisson
and
gaitdnbinomial
.
However, for gaitdlog
and gaitdzeta
one should be using
logffMlink
and
zetaffMlink
.
Without this function, the user must do quite a lot
of book-keeping to know which columns of the offset
matrix is to be assigned log(mux)
.
This can be rather laborious.
In the fictitional example below the response is underdispersed with respect to a Poisson distribution and doubling the response achieves approximate equidispersion.
Value
A matrix with n
rows and the same number of
columns that a GAITD regression would produce for
its matrix of linear predictors.
The matrix can be inputted into vglm
by assigning the offset
argument.
Note
This function is still in a developmental stage. The order of the arguments might change, hence it's safest to invoke it with full specification.
See Also
gaitdpoisson
,
gaitdlog
,
gaitdzeta
,
gaitdnbinomial
,
Trunc
,
offset
.
Examples
i.mix <- c(5, 10, 15, 20); a.mlm <- 13; mymux <- 2
goffset(mymux, 10, i.mix = i.mix, a.mlm = a.mlm)
## Not run: org1 <- with(gdata, range(y)) # Original range of the data
vglm(mymux * y ~ 1,
offset = goffset(mymux, nrow(gdata), i.mix = i.mix, a.mlm = a.mlm),
gaitdpoisson(a.mlm = mymux * a.mlm, i.mix = mymux * i.mix,
truncate = Trunc(org1, mymux)),
data = gdata)
## End(Not run)