Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: first anniversary of the IITS
Replies: 21   Last Post: Jan 10, 2015 4:01 PM

 Messages: [ Previous | Next ]
 clicliclic@freenet.de Posts: 1,245 Registered: 4/26/08
Re: first anniversary of the IITS
Posted: Mar 21, 2014 2:42 PM

Albert Rich schrieb:
>
> On Saturday, March 8, 2014 4:22:30 AM UTC-10, clicl...@freenet.de wrote:
>

> > My interest in Example 44 (like the similar but simpler 62, 64, 66, and
> > 118) was mostly in the asymmetric LN evaluation. Please fuse the ATAN's
> > in numbers 62, 64, 66 as you see fit; I find no continuity problems:
> >
> > ATAN(1 + SQRT(2)*SQRT(TAN(x))) - ATAN(1 - SQRT(2)*SQRT(TAN(x)))
> > = ATAN((TAN(x) - 1)/(SQRT(2)*SQRT(TAN(x)))) + pi/2
> >
> > [...]

>
> I revised the optimal antiderivatives for examples 62, 64, 66, 90, 91,
> 112 and 118 of Chapter 5 of the Timofeev integration test suite
> unifying arctangents as you suggested, and posted the results on the
> Rubi website at
>
> http://www.apmaths.uwo.ca/~arich/
>
> Note that the derivative of each side of the above equation are equal,
> so the unified arctangents can be used for antiderivatives. However,
> the two sides are not always equal assuming standard CCW
> (counter-clockwise) continuity is used along the arctangent's branch
> cut on the imaginary line. Interestingly the equation IS everywhere
> valid in Derive, since Derive uses CW continuity on the arctangent's
> branch cut...
>

It should be pointed out that paired ATAN's cannot always be fused
without continuity problems; consider

ATAN((1 - SQRT(3)*x)/SQRT(1-x^2)) - ATAN((1 + SQRT(3)*x)/SQRT(1-x^2))
= ATAN((1 - 2*x^2)/(SQRT(3)*x*SQRT(1-x^2))) ± pi/2

at x=0, for example.

The additive constants in the ATAN - ATAN = ATAN equations I gave apply
in Derive 6.10 on the real axis; often - and the more so on the complex
plane - they will be piecewise constants only. However, as you say, for
antiderivatives it suffices that the relations hold everywhere after
differentiation.

Just cosmetic defects are left to report in the Chapter 5 evaluations:
in Example 100, different versions of the radicand are employed in
parallel. And COS(2*x) could be used to advantage in the evaluations of
Examples 93-94, 96 and 117. A systematic check against the evaluations
in Timofeev's book, however, remains to be made.

Martin.