[R] symbolic computing example with Ryacas

Bert Gunter
2017-09-19T14:04:22Z

Have you studied the "Introduction to Ryacas" vignette that come with
the
package?

Cheers,
Bert



Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Tue, Sep 19, 2017 at 2:37 AM, Vivek Sutradhara <viveksutra at
gmail.com>
wrote:

> Hi all,
> I am trying to implement the following matlab code with Ryacas :
>
> syms U x x0 C
>
> d1=diff(U/(1+exp(-(x-x0)/C)),x);
>
> pretty(d1)
>
> d2=diff(U/(1+exp(-(x-x0)/C)),x,2);
>
> pretty(d2)
>
> solx2 = solve(d2 == 0, x, 'Real', true)
>
> pretty(solx2)
>
> slope2=subs(d1,solx2)
>
>
> I have tried the following :
>
> library(Ryacas)
>
> x <- Sym("x");U <- Sym("U");x0 <-
Sym("x0");C <- Sym("C")
>
> my_func <- function(x,U,x0,C) {
>
>   return (U/(1+exp(-(x-x0)/C)))}
>
> FirstDeriv <- deriv(my_func(x,U,x0,C), x)
>
> PrettyForm(FirstDeriv)
>
> slope <- yacas("Subst(x,x0),deriv(my_func(x,U,x0,C), x)")
>
> PrettyForm(slope)
>
>
> I don't understand how I should use the Subst command. I want the slope
of
> the first derivative at x=x0. How do I implement that?
>
> I would appreciate any help that I can get.
>
> Thanks,
>
> Vivek
>
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>
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