Re: [Maxima-discuss] A question about 1//2

[Barton W. <wi...@un...>]

> In some ways it would be better to use common lisp rationals.


Incidentally: there are several tests in the testsuite that pass  CL rationals and complex numbers to simplifya; two that I know of are


    is(part(?complex(1,2),0)="+")


    ?nformat(?/(1,2))


These might be good tests, but they are arguably bogus input--I know of no nonbogus test in the testsuite  that passes a CL rational or complex number to simplifya.


More Maxima trivia: Expand has the feature:


  (%i3) expand(exp(-x)/(1+x));
  (%o3) 1/(x*%e^x+%e^x)

No (so-called) expansion (controlled by mminusp, I think)

  (%i4) expand(exp(x)/(1+x));
  (%o4) %e^x/(x+1)

I have evidence that eliminating this expansion rule allows integrate(x^4/(a*x^2+x+c)^(5/2),x) to evaluate correctly, but  prevents specint(exp(-t)/(t+1)^2,t) from evaluating.

For evaluating integrate(x^4/(a*x^2+x+c)^(5/2),x), I'd guess that the expansion prevents Maxima from detecting a derivative divides opportunity.

I'd guess that if the rule x^(-y)/(a +b) --> 1/(a * x^y + b*x^y) only  worked when x is %e,  the testsuite would run OK and that the bug

   integrate(x^4/(a*x^2+x+c)^(5/2),x) --> nounform

would be fixed.



--Barton
________________________________
From: Raymond Toy <toy...@gm...>
Sent: Friday, June 23, 2017 3:49:20 PM
To: max...@li...
Subject: Re: [Maxima-discuss] A question about 1//2

>>>>> "Andreas" == Andreas Eder <and...@gm...> writes:

    Andreas> Hi,
    Andreas> i found that in the file ellipt.lisp we define the variable 1//2 like:
    Andreas> (defvar 1//2 '((rat simp) 1 2))
    Andreas> and in mopers.lisp there is a macro definition like:
    Andreas> (defmacro 1//2 () ''((rat simp) 1 2))

    Andreas> Does anybody know the reason - apart from mere historical
    Andreas> accident - for this situation. If there is one :-)

That was probably me and I didn't know about the other.

    Andreas> Shouldn't we unify thes uses?

Yes, we should.

    Andreas> The use of the macro definition looks clumsy to me, since it looks like
    Andreas> a function call for what should simply be the use of a constant. In
    Andreas> this
    Andreas> respect the variable definitions looks better.
    Andreas> Another approach would be to define a symbol macro.
    Andreas> What is your opinion about that?
    Andreas> I'm sure 1//2 is not the only case (there is also a definition of
    Andreas> half).
    Andreas> There a surely more such occurances.

Using a macro or symbol macro seems wasteful since there would be a
copy everywhere instead of just the one in the defvar.

--
Ray


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