makeRegressionFitnessFunction: Create a fitness function for symbolic regression
In rgp: R genetic programming framework

Creates a fitness function that calculates an error measure with respect to a given set of data variables. A simplified version of the formula syntax is used to describe the regression task. When an indsizelimit is given, individuals exceeding this limit will receive a fitness of Inf.

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makeRegressionFitnessFunction(formula, data, envir, errorMeasure = rmse,
  indsizelimit = NA, penalizeGenotypeConstantIndividuals = FALSE,
  subSamplingShare = 1)

`formula`	A formula object describing the regression task.
`data`	An optional data frame containing the variables in the model.
`envir`	The R environment to evaluate individuals in.
`errorMeasure`	A function to use as an error measure, defaults to RMSE.
`indsizelimit`	Individuals exceeding this size limit will get a fitness of `Inf`.
`penalizeGenotypeConstantIndividuals`	Individuals that do not contain any input variables will get a fitness of `Inf`.
`subSamplingShare`	The share of fitness cases s sampled for evaluation with each function evaluation. 0 < s ≤q 1 must hold, defaults to `1.0`.