[R] Fitting Richards' curve

[Abby Spurdle]

> It's possible that Martin's package, cobs, can do this, but not sure,
> I haven't tried it.
> And there may be other R packages for fitting splines/smoothers to
> data, subject to shape constraints.

Further to my previous post.
I read through the documentation for the cobs package.
And (someone please correct me if I'm wrong) I don't think it can
produce a smoother with an S-shaped shape constraint.
I found two other packages for smoothing under shape constraints, but
doesn't look like they can either.

I have code that could be adapted for this purpose.
But one it's incomplete, two it (currently) requires the user to
specify a smoothness parameter, and three doesn't produce any kind of
inference...