R help - Jun 2013 - evaluation of equations from Ryacas

Hello again.

Now I have the following:
> xx
[1] "Solve(1 - R/100==(2*y)/10000,R)"
> yacas(xx)
expression(list(R == 100 * (1 - 2 * y/10000)))
>
I would like to put in a value for y and obtain R.
I've tried more stuff with eval and Eval, but no luck yet.

Any suggestions would be much appreciated.

Thanks,
Erin


-- 
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodgess@gmail.com

	[[alternative HTML version deleted]]

Dear Erin,

Not exactly elegant, but
> e<-expression(list(R == 100 * (1 - 2 * y/10000)))
> ee <- e[[1]][2]
> ee
(R == 100 * (1 - 2 * y/10000))()
> eval(parse(text=(substring(paste(ee), 5))), list(y=5))
[1] 99.9

Regards
S?ren


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Erin Hodgess
Sent: 19. juni 2013 07:03
To: R help
Subject: [R] evaluation of equations from Ryacas

Hello again.

Now I have the following:
> xx
[1] "Solve(1 - R/100==(2*y)/10000,R)"
> yacas(xx)
expression(list(R == 100 * (1 - 2 * y/10000)))
>
I would like to put in a value for y and obtain R.
I've tried more stuff with eval and Eval, but no luck yet.

Any suggestions would be much appreciated.

Thanks,
Erin


--
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences University of Houston -
Downtown
mailto: erinm.hodgess at gmail.com

	[[alternative HTML version deleted]]

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On Wed, Jun 19, 2013 at 1:03 AM, Erin Hodgess <erinm.hodgess at gmail.com>
wrote:
> Hello again.
>
> Now I have the following:
>> xx
> [1] "Solve(1 - R/100==(2*y)/10000,R)"
>> yacas(xx)
> expression(list(R == 100 * (1 - 2 * y/10000)))
>>
Try the Ryacas Sym interface:
> library(Ryacas)
>
> R <- Sym("R")
> y <- Sym("y")
> ans <- Solve(R == 100 * (1 - 2 * y / 10000), R)
> ans
expression(list(R == 100 * (1 - 2 * y/10000)))
> Set(y, 3)
expression(3)
> ans
expression(list(R == 4997/50))
> Set(y, 4)
expression(4)
> ans
expression(list(R == 2498/25))


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