# Re: [Rd] extending the derivs table/fools rushing in

From: Ben Bolker <bolker_at_zoology.ufl.edu>
Date: Thu, 14 Aug 2008 13:07:52 -0400

has this change added as well.
However, I'm not as confident that this is the right thing to do? Should curly brackets even be appearing in mathematical expressions?

Ben

Gabor Grothendieck wrote:

```> While you are at it could you add { to the
> table so that this works:
>
```

>> # this is ok
>> f <- function(x) x*x
>> D(body(f), "x")
```> x + x
>
```

>> # but not g which is same as f
>> # except it has { ... } surrounding its body
>> g <- function(x) { x*x }
>> D(body(g), "x")
```> Error in D(body(g), "x") : Function '`{`' is not in the derivatives table
>
>
> 2008/8/14 Ben Bolker <bolker_at_zoology.ufl.edu>:
```

>> 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_S(PowerSymbol,
>> - PP_S(PlusSymbol,
>> - Constant(1.),
>> - PP_S2(ExpSymbol,
>> - Constant(-2.))),
>> - 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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>>
>>

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Received on Thu 14 Aug 2008 - 17:09:54 GMT

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