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Problem Report 2356 Details

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Report 2356 Actions

    Problem Report Number 2356
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Rejected (REJ)
    Problem Resolution ID REJ.X.0651
    Raised 2004-04-09 02:30
    Updated 2004-04-30 14:23
    Published 2004-04-30 14:23
    Product Standard Internationalised System Calls and Libraries Extended V3 (UNIX 03)
    Certification Program The Open Brand certification program
    Test Suite VSX4 version 4.6.2
    Test Identification XOPEN.os/maths/j0 9
    Specification Base Definitions Issue 6
    Problem Summary XOPEN.os/maths/j0 9 expects 0.0 for jn(x) when x is large.
    Problem Text This test fails because it expects a return value of 0.0 from jn(x)
    when x is large.

    According to Handbook of Mathematical Functions, Edited by M. Abramowitz
    et al; page 364, formula 9.2.1:

    Jn(x) ~ cos(x-(2n+1)*pi/4)*sqrt(2/x*pi) when x is large.

    This is what our implementation returns. The test should allow this
    value to be returned.
    Test Output
    ****************************************************************************************************************
    /tset/XOPEN.os/maths/j0/T.j0 9 Failed

    Test Description:
    When jn() is called with a second argument that is too large in
    magnitude or would cause underflow, then it returns zero and a
    range
    underflow error may occur.
    Note: This test is only executed in UNIX03 mode.

    Test Strategy:
    For UNIX03 modes:
    CREATE child process
    VERIFY that jn(n, maxdble) returns 0.0
    VERIFY that if an error is generated then this error is a
    range
    underflow error, using mlerrchk().

    Test Information:
    jn(2, maxdble) returned 4.18699e-155, expected 0.0


    ****************************************************************************************************************

    Review Information

    Review Type TSMA Review
    Start Date 2004-04-09 02:30
    Last Updated 2004-04-14 18:35
    Completed 2004-04-14 18:35
    Status Complete
    Review Recommendation Rejected (REJ)
    Review Response The formula given by the submitter is interesting mathematically, but
    I do not see how it can be of any value in a numeric computation of
    jn(2,x) for extremely large values of x such as DBL_MAX. Since x in
    this case is well beyond the point at which cos(x) suffers total loss
    of precision, the only information that the formula can usefully
    provide is that J2(x) lies in the range [-sqrt(2/x*pi), sqrt(2/x*pi)].

    I believe that this implementation is returning what is effectively
    a random value within that range, and that such behaviour does not
    comply with the XSH6 requirement that jn(2,x) should either return
    J2(x) or return 0.

    (I imagine the submitter may want to appeal this one, in which case
    it should go for expert review.)

    Review Type SA Review
    Start Date 2004-04-14 17:35
    Last Updated 2004-04-15 00:39
    Completed 2004-04-15 00:39
    Status Complete
    Review Resolution Rejected (REJ)
    Review Conclusion The SA does not find the argument in this PR sufficient to justify
    approval as a TSD and has therefore rejected it. We suggest the PR be
    sent for working group review under appeal.

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