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#831 integrate(sin(x)/cos(x)^2,x,0,%pi/3);

closed
nobody
5
2006-02-12
2005-12-06
Anonymous
No

Should return 1 but returns 0 if cos(x) is declared
positive.
Strange enough, if cos(x) is declared zero, maxima
returns the correct result.

poul.riis@skolekom.dk

Discussion

  • Raymond Toy
    Raymond Toy
    2006-01-28

    Logged In: YES
    user_id=28849

    The hint that the result is correct if cos(x) is declared
    zero is key.

    It seems the problem is in sin-cos-intsubs1 in defint.lisp.
    There's a clause there:

      \(\(not \(equal \($asksign denom\) '$zero\)\)
       0.\)
    

    This seems bizarre. If the denom is not zero, why should it
    return 0? My limited understanding is that sin-cos-intsubs1
    is supposed to substitute the limits of the integral into
    the indefinite integral. (Which, by the way is correctly
    computed by antideriv.)

    Changing it to read (equal ($asksign denom) '$zero)) makes
    more sense, but I don't know about returning zero as the
    result. Undefined or infinity seems better, if a choice
    must be made.

     
  • Raymond Toy
    Raymond Toy
    2006-02-12

    Logged In: YES
    user_id=28849

    Fixed as described, but we return '$undefined instead of 0,
    for want of a better solution. Seems better than 0 anyway.

     
  • Raymond Toy
    Raymond Toy
    2006-02-12

    • status: open --> closed