R: Specify the Parameter(s) of a Copula

setTheta {copula} | R Documentation

## Specify the Parameter(s) of a Copula

### Description

Set or change the parameter theta (`theta`) of a copula. The name ‘theta’ has been from its use in (nested) Archimedean copulas, where `x` is of class `"acopula"` or `"outer_nacopula"`. This is used for constructing copula models with specified parameter, as, for example, in `onacopula()`, or also `gofCopula`.

### Usage

    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)

    ## S4 method for signature 'acopula,ANY'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)
    ## S4 method for signature 'copula,ANY'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)
    ## S4 method for signature 'xcopula,ANY'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)
    ## S4 method for signature 'outer_nacopula,numeric'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)
    ## S4 method for signature 'khoudrajiCopula,ANY'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE, ...)

    ## S4 method for signature 'mixCopula,ANY'
    setTheta(x, value, na.ok = TRUE, noCheck = FALSE, freeOnly = TRUE,
             treat.negative = c("set.0", "warn.set0", "stop"), ...)

### Arguments

`x` | an R object of class `Copula`, i.e., any copula from package copula.
`value` | parameter value or vector, `numeric` or `NA` (when `na.ok` is true), corresponding to the “free” parameters.
`...` | further arguments for methods.
`na.ok` | logical indicating if `NA` values are ok for `theta`.
`noCheck` | logical indicating if parameter constraint checks should be skipped.
`freeOnly` | logical indicating that only non-fixed aka “free” parameters are to be set. If true as by default, `setTheta()` modifies only the free parameters of the copula; see also `fixParam`.
`treat.negative` | a `character` string indicating how negative mixture weights should be handled. If not `"stop"` which produces an error via `stop`, negative mixture weights are replaced by zero.

### Value

an R object of the same class as `x`, with the main parameter (vector) (often called `theta`) set to `value`.

### See Also

the “inverse” function, a “getter” method, is `getTheta()`.

### Examples

    myC <- setTheta(copClayton, 0.5)
    myC
    ## Frank copula with Kendall's tau = 0.8 :
    (myF.8 <- setTheta(copFrank, iTau(copFrank, tau = 0.8)))

    # negative theta is ok for dim = 2 :
    myF <- setTheta(copFrank, -2.5, noCheck=TRUE)
    myF@tau(myF@theta) # -0.262

    myT <- setTheta(tCopula(df.fixed=TRUE), 0.7)
    stopifnot(all.equal(myT, tCopula(0.7, df.fixed=TRUE),
                        check.environment=FALSE, tolerance=0))

    (myT2 <- setTheta(tCopula(dim=3, df.fixed=TRUE), 0.7))
    ## Setting 'rho' and 'df'  --- for default df.fixed=FALSE :
    (myT3 <- setTheta(tCopula(dim=3), c(0.7, 4)))

[Package copula version 1.0-1 Index]