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MathGroup Archive 2000

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Use of Miscellaneous`RealOnly` Package

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25253] Use of Miscellaneous`RealOnly` Package
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sun, 17 Sep 2000 04:47:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear MathGroup,

Is it possible to turn the Miscellaneous`RealOnly` package on and off?
Consider the following problem. I want to find the inverse of the following
function:

F[u_, v_] := {u^3, v - u}

eqns = Thread[F[u, v] == {x, y}]
{u^3 == x, -u + v == y}

sols = Solve[eqns, {u, v}][[1]]
{v -> x^(1/3) + y, u -> x^(1/3)}

If the above Solve is done with the RealOnly package active, it fails and
gives Nonreal for the answers. So I definitely don't want it active at this
point. Now I define the inverse:

FI[x_, y_] = ({u, v} /. sols)
{x^(1/3), x^(1/3) + y}

Now when I evaluate

FI[-10, -10] // N
{1.077217345015942 + 1.865795172362064*I, -8.922782654984058 +
   1.865795172362064*I}

I obtain the complex root, so I need to load RealOnly package.

<< Miscellaneous`RealOnly`
FI[-10, -10] // N
{-2.15443, -12.1544}

So sometimes I want it, and sometimes I don't want it. But there seems no
way to get rid of it other than quitting the kernel.

Does anyone have any suggestions, or a smoother way to do this problem?

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/



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