Re: What to do in v. 6 in place of

• To: mathgroup at smc.vnet.net
• Subject: [mg76829] Re: What to do in v. 6 in place of
• From: Helen Read <hpr at together.net>
• Date: Mon, 28 May 2007 01:00:12 -0400 (EDT)
• References: <f3bh1e\$37g\$1@smc.vnet.net>

```Bob Hanlon wrote:
> This works for simple cases such as your examples.
>
> Clear[realPlot];
> realPlot[expr_,
>    {x_Symbol, xmin_?NumericQ, xmax_?NumericQ},
>    opts___] := Module[{d, e, f, y},
>    e = Flatten@{expr};
>    d = (Denominator@PowerExpand@Log[x, #] & /@ e);
>    f = y /. (ToRules@
>          Reduce[y^#[[2]] == PowerExpand[#[[1]]^#[[2]]],
>           y, Reals] & /@ Thread[{e, d}]);
>    Plot[f, {x, xmin, xmax}, opts]];
>
> Grid[{{realPlot[x^(1/3), {x, -8, 8}],
>    realPlot[x^(3/5), {x, -8, 8}]},
>   {realPlot[{x^(1/3), x^(3/5)}, {x, -8, 8}]}}]

This completely misses the point, which is to make it easy for beginning
calculus students to plot functions such as x^(1/3) for negative x.
There is no way they could follow what you have written, let alone
reproduce it themselves.

Probably the best solution at this point is to simply use the old
Miscellaneous`RealOnly` package when this comes up in class, and just
ignore the "obsolete package" message.

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