Burcin Erocal wrote:
> On Friday 24 October 2008 15:17:57 Stan Schymanski wrote:
>> That's interesting. It seems that the bug lies in the use of floating
>> point numbers? By the way, simplify_trig and simplify_rational create
>> the same mistake. I agree that the use of simplify_radical() is not
>> very useful here, but if it makes such an obvious mistake, how
>> confident can we be that it doesn't make mistakes in more complicated
>> cases where we don't actually notice the mistake straight away? I
>> thought about using something like simplify_full() on any equation to
>> see if it can be simplified before I carry on with calculations.
>> Perhaps this is the wrong strategy, anyway. Any comments?
>> How could I actually get Sage to cancel out the 'a' in the equation?
>> None of the methods I tried do the job. I don't like doing things by
>> hand, because then I have to redo everything if I change an equation
>> somewhere at the top of the notebook.
>
> In this case, expand seems to do what you want. I don't know if it will help
> you with more complex expressions.
>
> sage: var("a,b,c")
> (a, b, c)
> sage: e = ((a*b - (1/2)*a*(b - c))/a); e
> (a*b - a*(b - c)/2)/a
> sage: e.expand()
> c/2 + b/2
>
> or with float coefficients:
>
> sage: e = ((a*b - (.5)*a*(b - c))/a); e
> (a*b - 0.500000000000000*a*(b - c))/a
> sage: e.expand()
> 0.500000000000000*c + 0.500000000000000*b
>
In general, I find that expand will end up simplifying things a lot more
than the simplify functions will.
I suppose it's like our secondary school math: when in doubt, multiply
everything out and then see what cancels.
Jason
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