R: Compute the log-sum or inclusive value/utility

logsum {mlogit} | R Documentation

## Compute the log-sum or inclusive value/utility

### Description

The `logsum` function computes the inclusive value, or inclusive utility, which is used to compute the surplus and to estimate the two steps nested logit model.

### Usage

        logsum(coef, X = NULL, formula = NULL, data = NULL,
               type = NULL, output = c("chid", "obs"))

### Arguments

`coef` | a numerical vector or a `mlogit` object, from which the `coef` vector is extracted,
`X` | a matrix or a `mlogit` object from which the `model.matrix` is extracted,
`formula` | a formula or a `mlogit` object from which the `formula` is extracted,
`data` | a `data.frame` or a `mlogit` object from which the `model.frame` is extracted,
`type` | either `"group"` or `"global"` : if a `group` argument has been provided in the `mlogit.data`, the inclusive values are by default computed for every group, otherwise, a unique global inclusive value is computed for each choice situation,
`output` | the shape of the results: if `"chid"`, the results is a vector (if `type = "global"`) or a matrix (if `type = "region"`) with row number equal to the number of choice situation, if `"obs"` a vector of length equal to the number of lines of the data in long format is returned.

### Details

The inclusive value, or inclusive utility, or log-sum is the log of the denominator of the probabilities of the multinomial logit model. If a `"group"` variable is provided in the `"mlogit.data"` function, the denominator can either be the one of the multinomial model or those of the lower model of the nested logit model.

If only one argument (`coef`) is provided, it should a `mlogit` object and in this case, the `coefficients` and the `model.matrix` are extracted from this model.

In order to provide a different `model.matrix`, further arguments could be used. `X` is a `matrix` or a `mlogit` from which the `model.matrix` is extracted. The `formula`-`data` interface can also be used to construct the relevant `model.matrix`.

### Value

either a vector or a matrix.

### Author(s)

Yves Croissant

### See Also

`mlogit` for the estimation of a multinomial logit model.

[Package mlogit version 0.3-0 Index]