#308 \"integrate\" asks if FALSE is pos, neg, or zero

closed
nobody
5
2007-12-15
2003-05-06
Robert Dodier
No

"integrate((1+erf(sqrt(1/u).(u-1)))/2,u,0,inf);" asks
if FALSE is positive, negative, or zero. That doesn't
seem like a meaningful question.

Since sqrt(1/u).(u-1) increases like sqrt(u), the
integrand approaches a positive constant (namely one)
and so the answer ought to be INF, I think.

I am running Maxima 5.9.0 on RedHat Linux 7.2.

Discussion

  • Robert Dodier
    Robert Dodier
    2004-11-25

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    attempt to fix title: replace ampersand-quot-semicolon w/
    quote marks (bug in sourceforge script, apparently)

     
  • Robert Dodier
    Robert Dodier
    2004-11-25

    • summary: "integrate" asks if FALSE is pos, neg, or zero --> "integrate" asks if FALSE is pos, neg, or zero
     
  • Robert Dodier
    Robert Dodier
    2005-05-16

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    Trying this with commutative multiplication instead of
    noncommutative (i.e.
    integrate((1+erf(sqrt(1/u)*(u-1)))/2,u,0,inf);) yields a
    noun form, without asking a question.

    Bug is still present in 5.9.1cvs from 3/31/2005 (clisp 2.33,
    linux).

     
  • Robert Dodier
    Robert Dodier
    2006-04-10

    • labels: --> Lisp Core - Integration
    • summary: "integrate" asks if FALSE is pos, neg, or zero --> \"integrate\" asks if FALSE is pos, neg, or zero
     
  • Harald Geyer
    Harald Geyer
    2007-06-08

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    It seem's the original problem has gone quite some time ago. I
    couldn't reproduce it under 5.11.0 nor 5.12.0. Now maxima asks
    an other (a little bit more meaningful) question:

    (%i2) integrate(1+erf(sqrt(u).(u-1)),u,0,inf);
    Is 'limit((1/sqrt(u)) . (1/u),u,0,plus) positive, negative, or zero? pos;
    (%o2) 'integrate(erf(sqrt(u) . (u-1))+1,u,0,inf)

    This seems to be the minimal example, where maxima asks
    this kind of question:

    (%i9) integrate(1+erf((u .u^2)),u,0,inf);
    Is 'limit(u . u^2,u,inf) positive, negative, or zero?pos;
    (%o9) 'integrate(erf(u . u^2)+1,u,0,inf)

    One might argue, that this question is ok, since it makes sense
    if the integral makes any sense at all. OTOH the handling
    of "." in integrals seems somewhat strange to me. Not sure
    whether this bug should be closed or not.

    This are futher cases:

    (%i17) integrate(1+erf((u^3 .u^2)),u,0,inf);
    Is 'limit(u^3 . u^2,u,inf) positive, negative, or zero?pos;
    (%o17) 'integrate(erf(u^3 . u^2)+1,u,0,inf)

    (%i18) integrate(1+erf((u^3 .u^n)),u,0,inf);
    Is 'limit(u^3 . u^n,u,inf) positive, negative, or zero?pos;
    (%o18) 'integrate(erf(u^3 . u^n)+1,u,0,inf)

    (%i11) integrate(1+erf((u .a)),u,0,inf);
    Is 'limit(u . a,u,inf) positive, negative, or zero?pos;
    (%o11) 'integrate(erf(u . a)+1,u,0,inf)

    In this cases maxima return a noun form or an actual answer
    without asking questions:

    (%i16) integrate(1+erf((u^2 .u^2)),u,0,inf);
    (%o16) 'integrate(erf((u^2)^^2)+1,u,0,inf)

    (%i12) integrate(1+erf((b .a)),u,0,inf);
    Integral is divergent -- an error. To debug this try debugmode(true);
    ... at least this is no worse than with other symbols.

    (%i8) integrate(1+erf((u^^2 .u^2)),u,0,inf);
    (%o8) 'integrate(erf(u^^2 . u^2)+1,u,0,inf)

     
  • Dan Gildea
    Dan Gildea
    2007-12-15

    • status: open --> closed
     
  • Dan Gildea
    Dan Gildea
    2007-12-15

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    I think the current behavior (described below) is fine.