[R] some questions about sympy (that is, rSymPy)

[Kjetil Halvorsen]

see below.

On Fri, Apr 13, 2012 at 8:50 PM, Kjetil Halvorsen
<kjetilbrinchmannhalvorsen at gmail.com> wrote:
> I am experimenting with rSymPy, and it seems to work nice.
>
>
> However, I dislike the need to wrap all sympy expressions within
> quotes, it leads to ugly calls like
> library(rSymPy)
> Var("x,y,z")
> sympy("(x+y)**2")
> and so on.
>
> Inspired by the function cq from mvbutiles package:
> library(mvbutils)
>> cq
> function (...)
> {
>    as.character(sapply(as.list(match.call(expand.dots = TRUE))[-1],
>        as.character))
> }
> <bytecode: 0x7fca88443f78>
> <environment: namespace:mvbutils>
>
> I tried to write
>> sympyq
> function(...) {
>   arg <- as.character(match.call(expand.dots=TRUE)[-1])
>   thiscall   <- as.call(list(as.name("sympy"), arg))
>   print( thiscall ) # for debugging
>   eval(thiscall, parent.frame() )
> }
>
> Some examples:
> (After doing
> Var("x,y,z") )
>> sympyq(4+4)
> sympy("4 + 4")
> [1] "8"
>
>> sympyq(3*x+4*y+89*z-6*x)
> sympy("3 * x + 4 * y + 89 * z - 6 * x")
> [1] "-3*x + 4*y + 89*z"
>>
>
> But then:
>
>> sympyq( (x+y)**2 )
> sympy("(x + y)^2")
> Error in .jcall("RJavaTools", "Ljava/lang/Object;", "invokeMethod", cl,  :
>  Traceback (most recent call last):
>  File "<string>", line 1, in <module>
> TypeError: unsupported operand type(s) for ^: 'Add' and 'int'
>
> Note that R has changed the  syntax **2 to ^2, which sympy does not
> seem to like!
>
> Any ideas for avoiding this, or more generally, better ideas for
> achieving what I am trying to do?
>
> Kjetil

Ok, I am trying now with

> sympyq
function(...) {
   arg <- as.character(match.call(expand.dots=TRUE)[-1])
   arg <- gsub('^', x=arg, replacement='**', fixed=TRUE)
   thiscall   <- as.call(list(as.name("sympy"), arg))
   print( thiscall )
   eval(thiscall, parent.frame() )
}

which gives:

> sympyq( (x+y)**2 )
sympy("(x + y)**2")
[1] "(x + y)**2"

> sympyq ( sin(pi) )
sympy("sin(pi)")
[1] "0"

> sympyq( limit(sin(x)/x, x, 0) )
sympy("limit(sin(x)/x, x, 0)")
[1] "1"

> sympyq( diff(sin(2*x), x, 2) )
sympy("diff(sin(2 * x), x, 2)")
[1] "-4*sin(2*x)"

so seems to work, but then, tyhe following I do not understand:

> sympyq( ((x+y)**2).expand() )
Error: unexpected symbol in "sympyq( ((x+y)**2).expand"

> sympyq( sin(x+y).expand(trig=True) )
Error: unexpected symbol in "sympyq( sin(x+y).expand"

???

Kjetil