R help - Sep 2017 - symbolic computing example with Ryacas

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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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
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/
> posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

Thanks for the response. Yes, I did study the vignette but did not
understand it fully. Anyway, I have tried once again now. I am happy to say
that I have got what I wanted.

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)")
slope <- Subst(FirstDeriv,x,x0)
#PrettyForm(slope) - gives errors
PrettyForm(Simplify(slope))

I was confused by the references to the yacas command.  Now, I have chosen
to omit it. Then I get what I want.
Thanks,
Vivek

2017-09-19 16:04 GMT+02:00 Bert Gunter <bgunter.4567 at gmail.com>:
> 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
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posti
>> ng-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
	[[alternative HTML version deleted]]