test=matrix(c( expression(x^3-5*x+4), expression(log(x^2-4*x)))) works. btw. you recieved an error because D expects an expression and you offered a list > class(test[1]) [1] "list" to get the error relating to the misuse of the tilde operator you have to prompt the "correct" extractor "[[" f<-test[[1]] D(f,"x")
Am Mon, 18 Sep 2006 18:30:57 +0200 schrieb Evan Cooch <[EMAIL PROTECTED]>: > Normally, I do symbolics in Maple, or Mathematica, but I'm trying to > write a simple script for students to handle some *very* simple > calculations (for other purposes) with matrix or vector elements, where > the elements are coded symbolically. What I've tried with *partial" > success is use of the tilde (~) operator. So, for example, consider a > simple vector: > > test=matrix(c(~ x^3-5*x+4, ~log(x^2-4*x))) > > Now, when I look at test, I see > > > test > [,1] > [1,] Expression > [2,] Expression > > Fine. When I try to extract one of the vector elements, I see (for > example) > > > test[1] > [[1]] > ~x^3 - 5 * x + 4 > > > Fine - but now I'm trying to figure out how to use the extracted matrix > element for anything else. For example, using D for simple symbolic > derivatives > > f <- test[1]; > D(f,"x") > > should *in theory* work, but I get the following: > > > D(f,"x"); > [1] NA > > But, if I try > > f <- expression(x^3-5*x+4); > D(f,"x"); > > works fine. > > So, even though it looks as if each element of test is coded as an > expression, it seems as though it is somehow a different type of > expression than if I code it explicitly as an expression. I'm *guessing* > it has to do with the tilde operator not assigning the formula to > anything, but I'm not sure. > > Suggestions? Pointers to the obvious? > > Thanks! > -- -------------------- Universität Hamburg Institut für Statistik und Ökonometrie Dipl.-Wi.-Math. Eik Vettorazzi Von-Melle-Park 5 20146 Hamburg Tel.: +49 40-42838-3540 ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
