[R] symbolic matrix elements...

[Tony Plate]

If I construct the matrix by list()ing together the expressions rather 
than c()ing, then it works OK:

 > x <- matrix(list( expression(x3-5*x+4), expression(log(x2-4*x))))
 > x[1,1]
[[1]]
expression(x3 - 5 * x + 4)

 > x[[1,1]]
expression(x3 - 5 * x + 4)
 > D(x[[1,1]], "x")
-5
 >

The reason c() doesn't work properly here might have something to do 
with it creating a language object of an unconventional type:

 > c( expression(x3-5*x+4), expression(log(x2-4*x)))
expression(x3 - 5 * x + 4, log(x2 - 4 * x))
 > expression(x3-5*x+4)
expression(x3 - 5 * x + 4)
 >

Using list() with language objects is much safer if you just want to 
make lists of them.

-- Tony Plate

Evan Cooch wrote:
> 
> Eik Vettorazzi wrote:
> 
>>test=matrix(c( expression(x^3-5*x+4), expression(log(x^2-4*x))))
>>works.
> 
> Well, not really (or I'm misunderstanding). Your code enters fine (no 
> errors), but I can't access individual elements - e.g., test[1,1] gives 
> me an error:
> 
>  > test=matrix(c( expression(x^3-5*x+4), expression(log(x^2-4*x))))
>  > test[1,1]
> Error: matrix subscripting not handled for this type
> 
> Meaning...what?
> 
> 
>>btw. you recieved an error because D expects an expression and you 
>>offered a list
> 
> 
> OK - so why then are each of the elements identified as an expression 
> which I print out the vector? Each element is reported to be an 
> expression. OK, if so, then I remain puzzled as to how this is a 'list'.
> 
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