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TypeError: ECL says: Maxima asks: Is y positive, negative, or zero?

asked 2013-10-20 03:22:35 -0500

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I'm using sage to give me the inverse of functions using solve(). Most of the time, it works fine. But when I have roots of anything involved(for example, "solve((5x-2)^(1/7)==y,x)", I get the error message in the title. Is there any way around this?

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answered 2013-10-20 04:35:14 -0500

updated 2013-10-20 07:17:44 -0500


The ECL lib complains because (to its mind) the answer depends on the fact that y being positive negative or zero. To specify some restriction on variables within Sage just do

sage: var('y')
sage: assume(y > 0)
sage: solve((5*x-2)^(1/7)==y,x)
[x == 1/5*y^7 + 2/5]

Now, the operation x -> x^(1/7) looks unamiguous on RR because x -> x^7 is a bijection on RR.

An alternative would be to rewrite the equation

sage: var('y')
sage: solve((5*x-2)==y^7,x)
[x == 1/5*y^7 + 2/5]
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Asked: 2013-10-20 03:22:35 -0500

Seen: 583 times

Last updated: Oct 20 '13