logLik.vlm {VGAM} | R Documentation

## Extract Log-likelihood for VGLMs/VGAMs/etc.

### Description

Calculates the log-likelihood value or the element-by-element contributions of the log-likelihood.

### Usage

    ## S3 method for class 'vlm'
    logLik(object, summation = TRUE, ...)

### Arguments

`object` | Some VGAM object, for example, having class `vglmff-class`.
`summation` | Logical, apply `sum`? If `FALSE` then a n-vector or n-row matrix (with the number of responses as the number of columns) is returned. Each element is the contribution to the log-likelihood.
`...` | Currently unused. In the future: other possible arguments fed into `logLik` in order to compute the log-likelihood.

### Details

By default, this function returns the log-likelihood of the object. Thus this code relies on the log-likelihood being defined, and computed, for the object.

### Value

Returns the log-likelihood of the object. If `summation = FALSE` then a n-vector or n-row matrix (with the number of responses as the number of columns) is returned. Each element is the contribution to the log-likelihood. The prior weights are assimulated within the answer.

### Warning

Not all VGAM family functions have had the `summation` checked.

### Note

Not all VGAM family functions currently have the `summation` argument implemented.

### Author(s)

T. W. Yee.

### See Also

VGLMs are described in `vglm-class`; VGAMs are described in `vgam-class`; RR-VGLMs are described in `rrvglm-class`; `AIC`.

### Examples

    zdata <- data.frame(x2 = runif(nn <- 50))
    zdata <- transform(zdata, Ps01    = logit(-0.5       , inverse = TRUE),
                              Ps02    = logit( 0.5       , inverse = TRUE),
                              lambda1 =  loge(-0.5 + 2*x2, inverse = TRUE),
                              lambda2 =  loge( 0.5 + 2*x2, inverse = TRUE))
    zdata <- transform(zdata, y1 = rzipois(nn, lambda = lambda1, pstr0 = Ps01),
                              y2 = rzipois(nn, lambda = lambda2, pstr0 = Ps02))

    with(zdata, table(y1))  # Eyeball the data
    with(zdata, table(y2))
    fit2 <- vglm(cbind(y1, y2) ~ x2, zipoisson(zero = NULL), data = zdata)

    logLik(fit2)  # Summed over the two responses
    sum(logLik(fit2, sum = FALSE))  # For checking purposes
    (ll.matrix <- logLik(fit2, sum = FALSE))  # nn x 2 matrix
    colSums(ll.matrix)  # log-likelihood for each response

[Package VGAM version 1.0-4 Index]