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Thread: Expm1() problems - precision

  1. #1
    Newbie
    Join Date
    Feb 2014
    Posts
    2

    Expm1() problems - precision

    Hi Guys.

    I created an OpenCL program to execute some mathematic operations. It worked fine in AMD video card (result matched with wolframalpha, for instance) but when I tried to use a computer with a Quadro 600 video card and linux, my program returned values that didn't matched the precision we expected for function expm1(x).
    I thought my video card had a problem, but I tried in another machine with quadro 600 and linux and obtained the same results from the first one.
    I tried run this program in Windows and I don't have this problem.

    Some examples:

    operation: expm1(input)
    output: -0.727467
    expected:-0.727468
    input: -1.3

    operation: expm1(input)
    output: 0.733252
    expected:0.733253
    input: 0.55

    operation: expm1(input)
    output: 0.822116
    expected:0.822119
    input: 0.6

    operation: expm1(input1)
    output: 0.915535
    expected:0.915541
    input 1: 0.65

    operation: expm1(input1)
    output: 991.271
    expected:991.275
    input 1: 6.9

    I've alread researched about this function ulp, but the maximun value is 1(full range)

    Is this a problem with the driver for linux?

    Thanks and Regards
    Rafael R. Machado

  2. #2
    Senior Member
    Join Date
    Oct 2012
    Posts
    105
    Indeed it works fine with Windows. I even get a precision of 1ulp instead of the 3ulps required by OpenCL specification.

    So it looks like a bug in the Linux driver.

  3. #3
    Newbie
    Join Date
    Feb 2014
    Posts
    2
    Thanks for the answer utnapishtim

    I'll continue this subject at the nVidia's fórum

    https://devtalk.nvidia.com/default/t...ems-precision/

    Thanks again
    Rafael R. Machado

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