mxJiggle {OpenMx} | R Documentation |

Jiggle free parameter values, subject to box constraints. `imxJiggle()`

is called internally by `mxTryHard()`

(q.v.). `mxJiggle()`

provides a more user-friendly wrapper to `imxJiggle()`

, and can alternately emulate the 'JIGGLE' behavior of classic Mx.

```
mxJiggle(model, classic=FALSE, dsn=c("runif","rnorm","rcauchy"), loc=1, scale=0.25)
imxJiggle(params, lbounds, ubounds, dsn, loc, scale)
```

`model` |
An object of class MxModel. |

`classic` |
Logical; should |

`dsn` |
Character string naming which random-number distribution–either uniform (rectangular), normal (Gaussian), or Cauchy–to be used to perturb free-parameter values. Defaults to the uniform distribution (for |

`loc` , `scale` |
Numeric. The location and scale parameters of the distribution from which random values are drawn to perturb free-parameter values, defaulting respectively to 1 and 0.25 (for |

`params` |
Numeric vector of current free parameter values. |

`lbounds` |
Numeric vector of lower bounds on parameters. |

`ubounds` |
Numeric vector of upper bounds on parameters. |

If `mxJiggle()`

argument `classic=FALSE`

(the default), `mxJiggle()`

calls `imxJiggle()`

. In that case, `mxJiggle()`

passes `imxJiggle()`

its own values for arguments `dsn`

, `loc`

, and `scale`

, and extracts values for arguments `params`

, `lbounds`

, and `ubounds`

from `model`

. Then, `model`

's free-parameter values are randomly perturbed before being re-assigned to it. The distributional family from which the perturbations are randomly generated is dictated by argument `dsn`

. The distribution is parameterized by arguments `loc`

and `scale`

, respectively the location and scale parameters. The location parameter is the distribution's median. For the uniform distribution, `scale`

is the absolute difference between its median and extrema (i.e., half the width of the rectangle); for the normal distribution, `scale`

is its standard deviation; and for the Cauchy, `scale`

is one-half its interquartile range. Free-parameter values are first multiplied by random draws from a distribution with the provided `loc`

and `scale`

, then added to random draws from a distribution with the same `scale`

but with a median of zero.

If `mxJiggle()`

argument `classic=TRUE`

, then each free-parameter value `x_i`

is replaced with `x_i + 0.1(x_i + 0.5)`

; this is the same behavior elicited in classic Mx by keyword JIGGLE.

`imxJiggle()`

returns a numeric vector of randomly perturbed free-parameter values. `mxJiggle()`

returns `model`

, with its free parameter values altered according to the other function arguments.

```
data(demoOneFactor)
manifests <- names(demoOneFactor)
latents <- c("G")
factorModel <- mxModel(
"One Factor",
type="RAM",
manifestVars = manifests,
latentVars = latents,
mxPath(from=latents, to=manifests,values=0.8),
mxPath(from=manifests, arrows=2,values=1),
mxPath(from=latents, arrows=2,
free=FALSE, values=1.0),
mxData(cov(demoOneFactor), type="cov",
numObs=500)
)
iniPars <- coef(factorModel)
print(iniPars)
pars2 <- imxJiggle(params=iniPars,lbounds=NA,ubounds=NA,dsn="runif",loc=1,scale=0.05)
print(pars2)
mod2 <- mxJiggle(model=factorModel,scale=0.05)
coef(mod2)
mod3 <- mxJiggle(model=factorModel,classic=TRUE)
coef(mod3)
```

[Package *OpenMx* version 2.21.11 Index]