I added "plogis" to the derivative table in the development version of R; the patch against yesterday's R-devel src/deriv/main.c is available at http://www.zoology.ufl.edu/bolker/deriv_patch.txt .
I pretty much followed the framework of the other symbols;
here was my incantation
- } else if (CAR(expr) == PlogisSymbol) {
- ans = simplify(TimesSymbol,
- PP_S(TimesSymbol,
- PP_S2(ExpSymbol,
- PP_S2(MinusSymbol,CADR(expr))),
- PP_S(PowerSymbol,
- PP_S(PlusSymbol,
- Constant(1.),
- PP_S2(ExpSymbol,
- PP_S2(MinusSymbol,CADR(expr)))),
- Constant(-2.))),
- PP(D(CADR(expr),var)));
- UNPROTECT(8);
It seems to work:
> D(quote(plogis(a)),"a")
exp(-a) * (1 + exp(-a))^-2
> D(quote(plogis(a+b*x)),"x")
exp(-(a + b * x)) * (1 + exp(-(a + b * x)))^-2 * b
Any thoughts? I'm sure there's a cleverer way to do this ...
Ben Bolker
PS I get a minor build error at the end of the compilation
(on Ubuntu 8.10):
make[2]: *** No rule to make target `VR.ts', needed by
`stamp-recommended'. Stop.
make[2]: Leaving directory
`/usr/local/src/R/R-devel/src/library/Recommended'
make[1]: *** [recommended-packages] Error 2
make[1]: Leaving directory
`/usr/local/src/R/R-devel/src/library/Recommended'
make: *** [stamp-recommended] Error 2
... don't know if that is important or not.
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