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Topic: An independent integration test suite
Replies: 128   Last Post: Dec 8, 2013 3:21 PM

 Messages: [ Previous | Next ]
 Waldek Hebisch Posts: 267 Registered: 12/8/04
Re: where the air gets thin for Axiom & Co.
Posted: Mar 26, 2013 8:26 AM

clicliclic@freenet.de wrote:
>
> Waldek Hebisch schrieb:

> >
> > clicliclic@freenet.de wrote:

> > >
> > > I bumped into this and am surprised by 70% failures (and not just
> > > timeouts) of the Axiom integrator on algebraic integrals possessing
> > > logarithmic antiderivatives that involve the single simple radical
> > > SQRT(x^3+1) or SQRT(x^4+1):
> > >
> > >
> > > This must be where the missing computation of the "splitting field
> > > of the Trager resultant" comes in.

> >
> > If one wants to describe the reason in one sentence, then yes.
> > [...]
> >
> > FYI, FriCAS contans code which in many cases avoids both
> > problems. Namely, FriCAS tries to split integral and
> > integrate parts separately. This handles the sqrt(1 + x^4)
> > cases. Currently in sqrt(1 + x^3) case FriCAS is unable
> > to find working split and gives up.
> >

A little correction (I wrote the above from memory): FriCAS
has problems with (1 + x^3)^(1/3). The sqrt(1 + x^3) seem
to work fine.

> Thanks for the explanation.
>
> If the failure to suitably split elementary integrals involving the
> radical sqrt(1 + x^3) = sqrt((1 + x)*(1 - x + x^2)) is somehow caused by
> the presence of an odd power in the radicand, the substitution t^2 =
> 1 + x might help, which introduces the radical sqrt(3 - 3*t^2 + t^4)
> where all powers of t are even. A better substitution would be t^2 =
> (1 - x + x^2)/(1 + x), which introduces sqrt(-3 + 6*t^2 + t^4), because
> here t remains real whenever the original radical is real.

Theoretically the sqrt(1 + x^3) is very easy. However, FriCAS does
not take any advantage of this special form and in fact changes
variables to produce IIRC square root of polynomial of degree 4.
To give more details: Trager algorithm produces expression
of form

\sum c_i*u_i

where each u_i has simple poles with integer residues. For
rational functions each u_i would produce a log term. In
algebraic case sometimes u_i directly give log term (this
is the case in Kauers examples) sometimes one must combine
several terms into one. Trager gave a method do decide if
a single u_i corresponds to a log. However, Trager test
only works if u_i has no poles at infinity. So Trager
must first change variables to remove poles at infinity.
This changes u_i, in particular in Kauers case each u_i
splits into two terms. Namely, one term corresponds to
poles of the logand, another to zeros of the logand.
Consequently, after change of variables single u_i
_never_ gives a log. one must always combine them.
FriCAS tries to find matching terms by looking at
terms that have residue differning only by signs.
This heuristic may fail if two logands have common
pole (or zero). Kauers examples put poles at infinity,
so there is common pole. In sqrt(x^4+1) there are
two poles at infinity and this seem to be the reason
that matching still works. In sqrt(x^3+1) Trager
test for logs may be modified to handle pole at
infinity, so there is no need to change variables
and then logs would be directly visible without
any need for matching. In (x^3+1)^3 case correct
way of matching terms is "obvious" for humans, but
not so easy to code in a general way.

Concerning you change of variables: it assumes knowledge
of some root of x^3+1. However, for irreducible cubic
root would introduce algebraic extension and that is
_very_ expensive for FriCAS.

--
Waldek Hebisch
hebisch@math.uni.wroc.pl

Date Subject Author
2/24/13 clicliclic@freenet.de
3/19/13 clicliclic@freenet.de
3/21/13 Waldek Hebisch
3/22/13 clicliclic@freenet.de
3/26/13 Waldek Hebisch
3/26/13 clicliclic@freenet.de
4/20/13 clicliclic@freenet.de
4/20/13 Nasser Abbasi
4/20/13 Rouben Rostamian
4/20/13 clicliclic@freenet.de
4/20/13 Rouben Rostamian
4/20/13 Axel Vogt
4/20/13 clicliclic@freenet.de
4/20/13 Axel Vogt
4/21/13 Axel Vogt
4/21/13 clicliclic@freenet.de
4/21/13 Waldek Hebisch
4/22/13 clicliclic@freenet.de
4/22/13 Axel Vogt
4/22/13 clicliclic@freenet.de
4/23/13 Waldek Hebisch
4/24/13 clicliclic@freenet.de
4/25/13 Waldek Hebisch
4/26/13 clicliclic@freenet.de
4/27/13 Waldek Hebisch
4/24/13 Richard Fateman
4/24/13 clicliclic@freenet.de
4/25/13 Richard Fateman
4/26/13 clicliclic@freenet.de
4/26/13 Axel Vogt
4/27/13 clicliclic@freenet.de
4/25/13 Waldek Hebisch
4/25/13 Peter Pein
4/25/13 Nasser Abbasi
4/26/13 Peter Pein
4/26/13 clicliclic@freenet.de
4/26/13 Peter Pein
4/26/13 clicliclic@freenet.de
4/26/13 Richard Fateman
4/27/13 clicliclic@freenet.de
4/27/13 Richard Fateman
6/30/13 clicliclic@freenet.de
6/30/13 Axel Vogt
7/1/13 clicliclic@freenet.de
7/1/13 Axel Vogt
7/1/13 Waldek Hebisch
7/2/13 clicliclic@freenet.de
7/2/13 clicliclic@freenet.de
7/2/13 clicliclic@freenet.de
7/2/13 Nasser Abbasi
7/2/13 Nasser Abbasi
7/4/13 clicliclic@freenet.de
7/4/13 Nasser Abbasi
7/4/13 Nasser Abbasi
7/5/13 clicliclic@freenet.de
7/5/13 Nasser Abbasi
7/9/13 clicliclic@freenet.de
7/10/13 Nasser Abbasi
7/10/13 Richard Fateman
7/10/13 Nasser Abbasi
7/10/13 clicliclic@freenet.de
8/6/13 clicliclic@freenet.de
9/15/13 Albert D. Rich
9/15/13 clicliclic@freenet.de
9/15/13 clicliclic@freenet.de
9/21/13 Albert D. Rich
9/21/13 clicliclic@freenet.de
9/22/13 daly@axiom-developer.org
9/24/13 daly@axiom-developer.org
9/30/13 daly@axiom-developer.org
9/22/13 Albert D. Rich
9/25/13 Albert D. Rich
9/25/13 Albert D. Rich
9/25/13 clicliclic@freenet.de
9/25/13 Albert D. Rich
9/26/13 Albert D. Rich
9/26/13 clicliclic@freenet.de
9/26/13 Albert D. Rich
9/29/13 clicliclic@freenet.de
10/1/13 Albert D. Rich
10/1/13 clicliclic@freenet.de
10/1/13 Albert D. Rich
10/5/13 clicliclic@freenet.de
10/5/13 Albert D. Rich
10/6/13 clicliclic@freenet.de
10/10/13 Albert D. Rich
10/10/13 Nasser Abbasi
10/11/13 clicliclic@freenet.de
11/6/13 Albert D. Rich
11/6/13 Nasser Abbasi
11/7/13 did
11/7/13 clicliclic@freenet.de
11/7/13 clicliclic@freenet.de
11/7/13 Albert D. Rich
11/12/13 clicliclic@freenet.de
11/12/13 Albert D. Rich
11/13/13 clicliclic@freenet.de
11/13/13 Albert D. Rich
11/14/13 clicliclic@freenet.de
11/14/13 Albert D. Rich
11/15/13 clicliclic@freenet.de
11/15/13 Albert D. Rich
11/16/13 clicliclic@freenet.de
11/16/13 clicliclic@freenet.de
11/21/13 Albert D. Rich
11/21/13 clicliclic@freenet.de
11/21/13 Nasser Abbasi
11/21/13 Albert D. Rich
11/21/13 Albert D. Rich
11/22/13 clicliclic@freenet.de
11/14/13 Albert D. Rich
11/15/13 clicliclic@freenet.de
11/15/13 Nasser Abbasi
11/16/13 clicliclic@freenet.de
11/16/13 Nasser Abbasi
11/7/13 did
11/7/13 clicliclic@freenet.de
4/20/13 Richard Fateman
4/21/13 clicliclic@freenet.de
4/20/13 Axel Vogt
4/20/13 clicliclic@freenet.de
4/20/13 Waldek Hebisch
4/21/13 G. A. Edgar
12/8/13 clicliclic@freenet.de
10/5/13 Albert D. Rich
10/6/13 clicliclic@freenet.de