From: Rolf Turner <rolf_at_math.unb.ca>

Date: Fri 05 Aug 2005 - 05:13:53 EST

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Aug 05 05:19:39 2005

Date: Fri 05 Aug 2005 - 05:13:53 EST

Martin C. Martin wrote:

> Rolf Turner wrote:

*>
**> >> deriv(expression(sum(x)), "x")
**> >>
**> >>
**> >
**> > does not make any sense.
**> >
**> >
**> Good point. But this does:
**>
**> deriv(expression(sum(log(a*x))), "a")
**>
**> where a is a scalar.
*

Okay --- I see what you're getting at now.

But I think that to get deriv() to handle expressions of that sort, i.e for deriv(expression(sum(log(a*x))), "a") not to fall over, requires more than ``putting sum in the derivatives table''. The problem is that ``sum'' is not the ``right sort of function''. Functions that appear in the derivatives table are (I think --- I am not knowledgable about this) functions of a single variable, like sin and cos and log, u.s.w. Whereas sum is a function of arbitrarily many variables. What is needed is for deriv() to know the rule that ``the derivative of a sum is the sum of the derivatives''. This would require rewriting the code of deriv(). Whether the required rule could be built into deriv() safely and sensibly is not clear to me. It might be do-able; I wouldn't want to try it, but! cheers, Rolf Turner rolf@math.unb.ca ______________________________________________R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Aug 05 05:19:39 2005

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