1\name{is.zero}
2\alias{is.zero}
3\alias{is.zero.matrix}
4\alias{is.zero.vglm}
5\title{Zero Constraint Matrices}
6\description{
7  Returns a logical vector from a test of whether an object such
8  as a matrix or VGLM object
9  corresponds to a 'zero' assumption.
10
11}
12\usage{
13is.zero.matrix(object, \dots)
14is.zero.vglm(object, \dots)
15}
16\arguments{
17  \item{object}{
18  an object such as a coefficient matrix of a \code{\link{vglm}} object,
19  or a \code{\link{vglm}} object.
20
21  }
22  \item{\dots}{
23  additional optional arguments.
24  Currently unused.
25
26  }
27}
28\details{
29  These functions test the effect of the \code{zero} argument
30  on a \code{\link{vglm}} object or the coefficient matrix
31  of a \code{\link{vglm}} object.
32  The latter is obtained by \code{coef(vglmObject, matrix = TRUE)}.
33
34
35
36}
37\value{
38  A vector of logicals, testing whether each linear/additive predictor
39  has the \code{zero} argument applied to it.
40  It is \code{TRUE} if that linear/additive predictor is
41  intercept-only, i.e., all other regression coefficients
42  are set to zero.
43
44  No checking is done for the intercept term at all, i.e., that
45  it was estimated in the first place.
46
47
48}
49\seealso{
50  \code{\link{constraints}},
51  \code{\link{vglm}}.
52
53
54}
55
56\examples{
57coalminers <- transform(coalminers, Age = (age - 42) / 5)
58fit <- vglm(cbind(nBnW,nBW,BnW,BW) ~ Age, binom2.or(zero = NULL), coalminers)
59is.zero(fit)
60is.zero(coef(fit, matrix = TRUE))
61}
62
63\keyword{models}
64\keyword{regression}
65