@abc.abstractproperty<EOL><INDENT>def PARAMLIMITS(self):<DEDENT>
pass<EOL>
Dict of tuples giving lower and upper allowed param values.

        For each `param` in `freeparams`, `PARAMLIMITS[param]`
        is a 2-tuple of floats giving upper and lower allowed
        values of `param` (or of each element in `param` if
        `param` is an array).