R help - Mar 2012 - sqrt(-x) vs. -x^0.5

Hi Everyone,

    I did a search through the archives and did not find an answer,
although I must admit it is a hard search to do ( ^0.5 is tough to
explicitly search for ).

    I am sure there is some mathematically accurate reason to explain the
following, but I guess I either never learned it or have since forgotten it.

    In 'R', when I type (for instance):

sqrt(-4)

    I get

NaN

    but if I type in:

-4 ^ 0.5

    I get

-2

    I presume this is on purpose and correct, but it's the first time
I've
come across any theoretical difference between ^0.5 and sqrt.  What is the
theoretical difference / meaning between these two operations?

                              Thanks!
                                   Mike


---
[The theory of gravity] is to me so great an absurdity that I believe no
Man who has in philosophical matters a competent faculty of thinking can
ever fall into it.  -- Isaac Newton

	[[alternative HTML version deleted]]

It's order of operations, and a good reason to always use
parentheses: which is evaluated first, the unary minus or
the raising-to-powers?

(-4)^0.5
-(4^0.5)

sqrt(-4)
-sqrt(4)

Sarah

On Wed, Mar 21, 2012 at 7:09 PM, Mike Williamson <this.is.mvw at
gmail.com> wrote:
> Hi Everyone,
>
> ? ?I did a search through the archives and did not find an answer,
> although I must admit it is a hard search to do ( ^0.5 is tough to
> explicitly search for ).
>
> ? ?I am sure there is some mathematically accurate reason to explain the
> following, but I guess I either never learned it or have since forgotten
it.
>
> ? ?In 'R', when I type (for instance):
>
> sqrt(-4)
>
> ? ?I get
>
> NaN
>
> ? ?but if I type in:
>
> -4 ^ 0.5
>
> ? ?I get
>
> -2
>
> ? ?I presume this is on purpose and correct, but it's the first time
I've
> come across any theoretical difference between ^0.5 and sqrt. ?What is the
> theoretical difference / meaning between these two operations?
>
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Thanks!
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Mike
>
-- 
Sarah Goslee
http://www.functionaldiversity.org