Update parameter values according to the different options 'abs', 'rep', and 'rel'

update_par(par, par_up, change, to_chg)

Arguments

par	Vector with parameter values that are updated
par_up	Value that is applied to the paramter values for updating
change	Type of change, either: abs', 'rep', or 'rel'
to_chg	Index vector that indicates the values of the parameter vector that should be updated