On entry: the point at which components of the solution and derivative are to be evaluated.
twant should not normally be an extrapolation point, that is
twant should satisfy
or if integration is proceeding in the negative direction
where
is the previous integration point and is, to within rounding,
tcurr –
hlast (see
d02qxf). Extrapolation is permitted but not recommended and
is returned whenever extrapolation is attempted.