[R] Obtain gradient at multiple values for exponential decay model

[David Winsemius]

> On Apr 6, 2018, at 3:43 AM, g l <gnulinux using gmx.com> wrote:
> 
>> Sent: Friday, April 06, 2018 at 5:55 AM
>> From: "David Winsemius" <dwinsemius using comcast.net>
>> 
>> 
>> Not correct. You already have `predict`. It is capale of using the `newdata` values to do interpolation with the values of the coefficients in the model. See: 
>> 
>> ?predict
>> 
> 
> The § details did not mention interpolation explicity; thanks.
> 
>> The original question asked for a derivative (i.e. a "gradient"), but so far it's not clear that you understand the mathematical definiton of that term. We also remain unclear whether this is homework.
>> 
> 
> The motivation of this post was simple differentiation of a tangent point (dy/dx) manually, then wondering how to re-think in modern-day computing terms. Hence the original question about asking the appropriate functions/syntax to read further ("curiosity"), not the answer (indeed, "homework"). :)
> 
> Personal curiosity should be considered "homework".

Besides symbolic differentiation, there is also the option of numeric differentiation. Here's an amateurish attempt:

myNumDeriv <- function(x){ (exp( predict (graphmodeld, newdata=data.frame(t=x+.0001))) - 
                                            exp( predict (graphmodeld, newdata=data.frame(t=x) )))/
                                          .0001 }
myNumDeriv(c(100, 250, 350))



David Winsemius
Alameda, CA, USA

'Any technology distinguishable from magic is insufficiently advanced.'   -Gehm's Corollary to Clarke's Third Law