Allow the user to set and examine a variety of ROI options like the default
solver or the function used to compute the gradients.
Usage
ROI_options(option, value)
Arguments
option
any options can be defined, using 'key, value' pairs.
If 'value' is missing the current set value is returned for the given 'option'.
If both are missing. all set options are returned.
value
the corresponding value to set for the given option.