16 Feb 17:05 2013

## Bug 2546: Solve with duplicate equations

Rupert Swarbrick <rswarbrick <at> gmail.com>

2013-02-16 16:05:12 GMT

2013-02-16 16:05:12 GMT

A few days ago, bug 2546 was filed [1], describing slightly inconsistent behaviour of solve() when given duplicate equations. Transcript: (%i1) solve([sin(x)=cos(x), sin(x)=cos(x)],x); (%o1) [] (%i2) solve([sin(x)=cos(x)],x); (%o2) [sin(x) = cos(x)] (solve() doesn't actually return anything helpful in either case, but that's not really what the bug is about) What's going on is that $SOLVE calls either SSOLVE (for a single equation) or SOLVEX (for multiple equations). When they can't find any useful solution, their behaviour is different. We could insert a call to REMOVE-DUPLICATES on the equation list before deciding what to do, but I think this would be fooled by pretty obviously identical equations (eg. x+y and y+x are different; x*(1+x) and x+x^2 are different...). I'm not sure whether it makes much sense to try and do anything cleverer - calling expand on the equations might be a bit bonkers... So, in my opinion, this isn't really a bug. The weird behaviour is that SSOLVE returns a sort of partial result when it gets stuck and SOLVEX returns an empty list. Weirdness like this is why I don't call solve() in scripts and instead rely on eg. algsys() where at least I know what I'll get if it fails. Does anyone have strong feelings here? Otherwise, I'll close the bug as wontfix (or more like "wontfix any time soon, sorry"). Rupert [1] https://sourceforge.net/p/maxima/bugs/2546/

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