[R] symbolic computing example with Ryacas
Vivek Sutradhara
viveksutra at gmail.com
Tue Sep 19 11:37:33 CEST 2017
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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