Odp: ^ operator
On 16-Nov-09 13:13:27, Liviu Andronic wrote:
On 11/16/09, Ted Harding <Ted.Harding at manchester.ac.uk> wrote:
Not in this case (see below), though of course in general "-" takes precedence over "^", so, for example, in the expression -2^(1/3) the "-" is applied first, giving (-2); and then "^" is applied next, giving (-2)^(1/3). There is a work-round (see below).
Hmm.. I may be doing something wrong, but from here it looks to be the opposite.
-2^(1/3); -(2)^(1/3); -(2^(1/3));
[1] -1.2599 [1] -1.2599 [1] -1.2599
(-2)^(1/3)
[1] NaN The results don't change when switching from the unary minus.
0-2^(1/3); 0-(2)^(1/3); 0-(2^(1/3));
[1] -1.2599 [1] -1.2599 [1] -1.2599
Correct!!! I was inadvertently put on the wrong foot by Pietr Pikal's comment about precedence, and as a result what I wrote about precedence of "^" relative to "-" was on the wrong foot throughout, and should be ignored. My apologies for any confusion this may have caused to anybody. In any case, this is not relevant to Carol White's query about taking the cube root (or indeed any fractional power) of a negative number. This can only be done (as Carol intended it) by using the form sign(x)*(abs(x)^power). As I tried to point out, there is a distinction between an expression which the user may enter as x <- -1.234, and then x^(1/3), expecting -(1.234^(1/3)), and the cube root of the negative number x. Ted.
It seems to me that in this example "^" is applied first, and "-" second. There is also this fortune entry.
fortune("unary")
Thomas Lumley: The precedence of ^ is higher than that of unary minus.
It may be surprising,
[...]
Herv?? Pag??s: No, it's not surprising. At least to me... In the
country
where I grew up, I've
been teached that -x^2 means -(x^2) not (-x)^2.
-- Thomas Lumley and Herv?? Pag??s (both explaining that operator
precedence is working
perfectly well)
R-devel (January 2006)
Liviu
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