[R] Combining expressions.

[Turner Rolf]

I am trying to construct a function to which I pass an expression as an argument.
>From that expression I want to create a somewhat more complicated expression
and then differentiate it using D() or deriv().

To give a simple example, I'd like to be able to do something like

e1 <- expression(x^2 + y^2)
e2 <- some.magic(e1,"n")

or maybe e2 <- some.magic(e1,expression(n))

and get e2 being expression((x^2+y^2)^n).  (Whence I can then do D(e2,"x") and D(e2,"y").)

Is there any way to accomplish this?

Thanks.

        cheers,

         Rolf Turner
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