simplify not working properly with complex numbers

[Julia Goedecke]

Hello,
I have searched through the back catalogue of numbas-users emails, but
not found what I'm looking for (I have the vague memory of seeing it
before, but perhaps I've just come across a similar problem before)

When I use simplify with some complex number variables in an expression,
the "minus" signs are not resolved properly so I get things like - -2i z.

Has anyone come across this before and knows a workaround?

Julia
--
www.julia-goedecke.de

[Ben Brawn]

This sounds like something Christian would want to see an example of in a question. I haven't heard or seen the double negative thing before.

[Julia Goedecke]

Hello,
I have made a question which demonstrates the problem and a possible
workaround for some cases:

https://numbas.mathcentre.ac.uk/question/share/view/93699eff-c5ae-418d-8eeb-2d0186261c6b

Julia

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[Christian Lawson-Perfect]

Thanks, Julia.

I'm sorry I haven't had time to look at this yet - the EAMS conference and stuff at Newcastle have taken up all my time this week. Hopefully I'll have a moment next week!

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[Christian Lawson-Perfect]

OK, I've sorted these out. The examples were very helpful, thanks Julia.

The problem was that the rule for pulling negation to the outside of a string of multiplications didn't deal with negative imaginary numbers. Complex numbers are quite finicky: they can either be represented algebraically, as an abstract expression of the form `a+b*i`, or as a single "complex number" token - typically this happens when you substitute a number into an expression.

I think I've made the right change to the simplification rules to make it deal with these cases.