options: User-configurable options
In ClimDown: Climate Downscaling Library for Daily Climate Model Output

ClimDown has a number of global options with sensible defaults pre-set. Options must be configured using R's options function. They can be set by using an .Rprofile file, or on the R session prompt prior to executing any ClimDown wrapper functions.

`max.GB`	An approximate measure of how much RAM to use in the chunk I/O loop. In reality, R does a lot of copying data, so if you have a firm RAM threshold, it's best to set this to about 1/3 to 1/4 of what you want the high-water mark to be. (default=1)
`trimmed.mean`	Undocumented and not recommended to change. (default=0)
`delta.days`	Undocumented and not recommended to change. (default=45)
`n.analogues`	The number of temporal analogues that the CA algorithm will search for and match. The higher this number, the longer the execution time of the reordering step. (default=30)
`calibration.start`	A POSIXct object that defines the beginning of the calibration period. (default=`as.POSIXct('1971-01-01', tz='GMT')`)
`calibration.end`	A POSIXct object that defines the end of the calibration period. (default=`as.POSIXct('2005-12-31', tz='GMT')`)
`tol`	Undocumented and not recommended to change. (default=0.1)
`expon`	Undocumented and not recommended to change. (default=0.5)
`multiyear`	Undocumented and not recommended to change. (default=TRUE)
`expand.multiyear`	Undocumented and not recommended to change. (default=TRUE)
`multiyear.window.length`	Undocumented and not recommended to change. (default=30)
`trace`	Undocumented and not recommended to change. (default=0.005)
`jitter.factor`	Undocumented and not recommended to change. (default=0.01)
`tau`	Undocumented and not recommended to change. (default=`list(pr=1001, tasmax=101, tasmin=101)`)
`seasonal`	Undocumented and not recommended to change. (default=`list(pr=TRUE, tasmax=FALSE, tasmin=FALSE)`)
`ratio`	Undocumented and not recommended to change. (default=`list(pr=TRUE, tasmax=FALSE, tasmin=FALSE)`)
`check.units`	A boolean value that determines whether to check the input units and convert them to the target output units. The safe option is to leave this set to TRUE, but if know for sure that the units match, modest performance gains can be made by not checking and performing this conversion. (default=TRUE)
`check.neg.precip`	A boolean value that determines whether to check for and eliminate negative precipitation values. Like check.units, modest performance gains can be achieved if you are certain that no negative precipitation values exist. (default=TRUE)
`target.units`	A list containing the units that should be used for the output file (default=`c(tasmax='celsius', tasmin='celsius', pr='kg m-2 d-1')`)