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Solving system of inequalities in one variable

asked 2015-05-26 04:38:05 -0600

anonymous user

Anonymous

I am probably missing something about how to use sage:

If I run this:

x = var('x')
a = var('a')
solve([a*x>0,a>0],[x])

I get this results:

[[0 < x, a > 0], [x < 0, -a > 0, a > 0]]

However, I would expect something like:

[0 < x, a > 0]

What am I missing?

Thanks

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rws gravatar imagerws ( 2015-07-15 04:08:08 -0600 )edit

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answered 2015-05-27 07:51:38 -0600

tmonteil gravatar image

updated 2015-05-27 07:52:28 -0600

Formally, there is nothing wrong since the second list of inequalities leads to the empty set (because of -a > 0, a > 0). That said, one could indeed expect that that list would have been automatically removed. In general, the solve function is not reliable since it might fail silently (e.g. give less solution than expected), for such systems of inequelities, an alternative is to use qepcad, whose installation is unfortunately currently broken (it used to be an experimental package).

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Asked: 2015-05-26 04:38:05 -0600

Seen: 206 times

Last updated: May 27 '15