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On 8/05/2009, at 7:10 PM, steve donovan wrote:
On Fri, May 8, 2009 at 12:01 AM, Geoff Leyland <geoff_leyland@fastmail.fm> wrote:I've had a quick look at your code, but I can't work this one out: what's the result of differentiating 3*x^2 + 5*x^2? That is, does it gather termsthat aren't exactly alike?Yes, Houston, we do have a problem: + 3 * 2 * x + 5 * 2 * x (unfolded result) - 6 * x + 10 * x (folded result) Obviously it's missing an opportunity for simplification, but I don't know how to express it generally yet.
I cheat for this: I separate any coefficient from the rest of the expression, make sure that the rest of the terms are ordered alphabetically, and then compare string representations:
3 * x * y + 5 * y * x =>
terms["x*y"] = { coeff=3, expression=x * y}
and then
terms["x*y"].coeff += 5
It's dirty but it works well enough. For my purposes, I don't want to
transform x * z + y * z into (x + y) * z, which would be quite a bit
tougher.
And collaboration would be most cool.
Yes. I've already pinched some good ideas from your code, thanks, so I figure I owe you.