MVNcov | R Documentation |

Maximum likelihood estimation of the Multivariate Normal distribution. The covariances (not correlation coefficients) are included in the parameter vector.

```
MVNcov(zero = c("var", "cov"),
lmean = "identitylink",
lvar = "loglink",
lcov = "identitylink")
```

`zero` |
Integer or character–string vector.
Which linear predictors are intercept–only.
Details at |

`lmean, lvar, lcov` |
VGLM–link functions applied to the means, variances and covariances. |

For the `K`

–dimensional normal distribution,
this fits a linear model to the `K`

means
`\mu_j`

`j = 1, \ldots, K`

, which are the
first entries in the linear predictor. The variances
`\sigma^2_j`

`j = 1, \ldots, K`

and then the covariances
`cov_{ij}`

```
i = 1, \ldots, K,
j = i + 1, \ldots, K
```

, are next aligned.
The fitted means are returned as the fitted values.

The log–likelihood is computed via
`dmultinorm`

,
an implementation of the multivariate Normal density.

The score and expected information matrices are internally computed at each Fisher scoring step, using its vectorized form.

The response should be an `K`

–column matrix.
The covariances may be any real number so that
the `identitylink`

is a reasonable choice.
For further details on VGLM/VGAM–link functions, see
`Links`

.

An object of class `"vglmff"`

(see `vglmff-class`

) to be
used by VGLM/VGAM modelling functions, e.g.,
`vglm`

or `vgam`

.

Unlike other implementations, e.g.,
`binormal`

from
VGAM in terms of `\rho`

and standard deviations,
`MVNcov`

estimates
the variances and covariances, modeled as intercept–only.
See argument `zero`

, whose default is `c("var", "cov")`

,
to change this.

Thus far, there is no guarantee that the estimated var–cov matrix will be
positive–definite. Proper procedures to validate this will
be incorporated shortly, such as the `@validparams`

slot.

Although the function has been tested on `K \leq 5`

data sets, it is recommended that `K \leq 3`

,
unless the data are *nice* and `n`

is sufficiently large.

Victor Miranda.

`dmultinorm`

,
`binormal`

,
`CommonVGAMffArguments`

,
`vglm`

.

```
# K = 3.
set.seed(180227)
nn <- 85
mvndata <- data.frame(x2 = runif(nn), x3 = runif(nn))
mvndata <- transform(mvndata,
y = rbinorm(nn, mean1 = 2 - 2 * x2 + 1 * x3,
mean2 = 2 - 1.5 * x3,
var1 = exp(1.0), var2 = exp(-0.75),
cov12 = 0.5 * exp(1.0) * exp(-0.75)))
mvndata <- transform(mvndata, y3 = rnorm(nn, mean = 2 + x2, sd = exp(1.5)))
colnames(mvndata) <- c("x2", "x3", "y1", "y2", "y3")
mvnfit <- vglm(cbind(y1, y2, y3) ~ x2 + x3, MVNcov, data = mvndata, trace = TRUE)
(mvncoef <- coef(mvnfit, mat = TRUE))
## Check variances and covariances: var1, var2 and var3.
exp(mvncoef[c(10, 13, 16)]) # True are var1 = exp(1.0) = 2.718,
# var2 = exp(-0.75) = 0.472
# and var3 = exp(1.5)^2 = 20.08554
vcov(mvnfit)
constraints(mvnfit)
summary(mvnfit)
```

VGAMextra documentation built on Nov. 2, 2023, 5:59 p.m.

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