Semyon Glazyrin wrote:
> Hello!
>
> When I try to integrate one simple expression maxima asks me about
> sign of one subexpression. But I think in this case integral limits
> answer the question:
>
> (%i2) assume(a>0,b>0);
> (%o2) [a > 0, b > 0]
> (%i3) integrate(sqrt(a/x-b),x,0,a/b);
> Is b x - a positive, negative, or zero?
>
> n; %pi a
> (%o3) ---------
> 2 sqrt(b)
>
> Does maxima do such type of checks?
Unfortunately this tendency to ask signs is a really serious problem of
maxima. The person who introduced "asksign" in the system did a very bad
choice for many reasons.
* First, rules as sqrt(x^2)=abs(x) are stories for little children. They
have no sense whatsoever as soon as one works with complex numbers.
A square root has two values, period. Choosing cuts like the negative real
axis is totally arbitrary, and a nonsense for complex roots.
* Second, a practical reason, nobody doing a not completely trivial
computation (and for a trivial one, maxima is not necessary) has any reason
to know the answer to the question.
* Third, it makes running maxima under another system, like in Sage,
difficult at best.
>
> thanks,
> Semyon.
--
Michel Talon