[R] Save values from an expression that is created from deriv command

[Gabor Grothendieck]

Try this:

D(expression(x*x), "x")


On Sat, May 23, 2009 at 12:46 PM, dimitris kapetanakis
<gamitor at gmail.com> wrote:
>
> Dear all,
>
> I want to save a value from an expression that I created by using the deriv
> function. So for example the output from an expression using the deriv
> command is:
>
> expression({
>    .expr7 <- 4 * b.nox.2^2 - 12 * b.nox.3 * b.nox.1
>    .expr9 <- -2 * b.nox.2 - sqrt(.expr7)
>    .expr10 <- 6 * b.nox.3
>    .value <- .expr9/.expr10
>    .grad <- array(0, c(length(.value), 1L), list(NULL, c("b.nox.3")))
>    .grad[, "b.nox.3"] <- 0.5 * (12 * b.nox.1 * .expr7^-0.5)/.expr10 -
>        .expr9 * 6/.expr10^2
>    attr(.value, "gradient") <- .grad
>    .value
> })
>
> The problem is that I do not know how to store the:
>
> .grad[, "b.nox.3"] <- 0.5 * (12 * b.nox.1 * .expr7^-0.5)/.expr10 -
>        .expr9 * 6/.expr10^2
>
> and then use its numerical value in my code.
>
> How can I store the above value or any output from the expression from deriv
> command so I can use it later in the code?
>
> Any help would be highly appreciated
>
> Thanks
>
> Dimitris
> --
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