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I have a list of polynomial equations that represent constraints on a system, but they are not independent and are therefore some are redundant.

my real list is very long. A simple example would be

eqns = {x^2+y^2 == 1, -x^2-y^2 == -1}

I'm not trying to (nor could I) solve the system of equations. I'd just like to have a list that contains only independent constraints. Is there a way to achieve this?

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    $\begingroup$ You can Simplify all the equations and then use DeleteDuplicates like this: Simplify /@ {x^2 + y^2 == 1, -x^2 - y^2 == -1} // DeleteDuplicates $\endgroup$ May 18, 2017 at 3:32
  • $\begingroup$ Simplify is leaving the equations in a non-identical format (eg out by an overall minus sign) so DeleteDuplicates does not recognise them as being duplicates $\endgroup$ May 18, 2017 at 3:40
  • $\begingroup$ Did the above code work for those equations? $\endgroup$ May 18, 2017 at 3:51
  • $\begingroup$ it does seem to work when I incorporate my eqtns in code you specify but not when I simplify them independently then perform DeleteDuplicates after. Does your simplify code somehow enforce a more uniform result from Simplify? $\endgroup$ May 18, 2017 at 3:55
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    $\begingroup$ It seems that Eliminate[eqns, {}] would do the trick? Could you give more examples or explain more about the real equations? $\endgroup$
    – rhermans
    May 18, 2017 at 10:11

1 Answer 1

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I think this question deserves a formal answer.

Let;s work a slightly more complicated example.

eqns = {x^2 + y^2 == 1, -x^2 - y^2 + 1 == 0, 5 x - 1 == y, y == 5 x - 1};
eqns // Simplify // DeleteDuplicates

{x^2 + y^2 == 1, 5 x == 1 + y}

The idea is to regularize the equations and delete the duplicates.

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