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The description of the ATAN2 function in Microsoft Excel is not 1.

  1. #1
    Celeste
    Guest

    The description of the ATAN2 function in Microsoft Excel is not 1.

    The description of the ATAN2 function in Microsoft Excel help does not seem
    100% accurate to me. It states "ATAN2(a,b) equals ATAN(b/a), except that a
    can equal 0 in ATAN2. "

    I don't think that is accurate because ATAN2 takes into account the quadrant
    in which z lies and has the range of -pi to pi (excluding -pi). This
    special inverse tangent uses the sign of x and y to determine the quadrant,
    and allows for answers in quandrant 2 (-x, +y) and quadrant 3
    (-x,-y) whereas the standard arctan is restricted to quadrants 1 and 4
    (range of -pi/2 to +pi/2).

    There are cases in which ATAN(y/x) does not equal ATAN2(x,y), other than
    when x = 0. For example, when x = -5 and y =-15, ATAN(-15/-5) = 1.249 and
    ATAN2(-5,-15) = -1.89

    I'm not a math expert, but this description seems misleading to me. I
    suggest a description similar to the C++ ATAN2(x,y) function "The atan2()
    function computes the arc tangent of y/x, using the signs of the arguments to
    compute the quadrant of the return value. "


  2. #2
    Harlan Grove
    Guest

    Re: The description of the ATAN2 function in Microsoft Excel is not 1.

    "Celeste" <Celeste@discussions.microsoft.com> wrote...
    >The description of the ATAN2 function in Microsoft Excel help does not
    >seem 100% accurate to me. It states "ATAN2(a,b) equals ATAN(b/a), except
    >that a can equal 0 in ATAN2. "

    ....

    Yes, this is inaccurate except for x and y > 0.

    >There are cases in which ATAN(y/x) does not equal ATAN2(x,y), other than
    >when x = 0. For example, when x = -5 and y =-15, ATAN(-15/-5) = 1.249 and
    >ATAN2(-5,-15) = -1.89


    This has everything to do with quadrants. In this case, the ATAN result is
    angularly displaced 180 degrees from the ATAN2 result. The ATAN result is
    1.249 radians counterclockwise from the positive X axis, and the ATAN2
    result is 1.89 radians clockwise from the positive X axis, which happens to
    be 1.249 radians counterclockwise from the negative X axis.

    >I'm not a math expert, but this description seems misleading to me.
    >I suggest a description similar to the C++ ATAN2(x,y) function . . .


    You're making the understandable but naive assumption anyone within
    Microsoft wants to expend any effort or resources fixing their
    documentation. This isn't the only place Excel's documentation (aka online
    help) is misleading or just plain wrong.



  3. #3
    Tushar Mehta
    Guest

    Re: The description of the ATAN2 function in Microsoft Excel is not 1.

    Hi Celeste,

    You are right. ATAN2 can do with a better explanation. As can many
    other XL functions. {g}

    I'll see if someone among my limited contacts within MS -- I am not
    particularly astute at networking {vbg} -- is willing to follow up and
    improve the documentation. But, I wouldn't hold my breath expecting a
    change any time soon.

    --
    Regards,

    Tushar Mehta
    www.tushar-mehta.com
    Excel, PowerPoint, and VBA add-ins, tutorials
    Custom MS Office productivity solutions

    In article <35496788-BFED-4210-AC4E-79537480D814@microsoft.com>,
    Celeste@discussions.microsoft.com says...
    > The description of the ATAN2 function in Microsoft Excel help does not seem
    > 100% accurate to me. It states "ATAN2(a,b) equals ATAN(b/a), except that a
    > can equal 0 in ATAN2. "
    >
    > I don't think that is accurate because ATAN2 takes into account the quadrant
    > in which z lies and has the range of -pi to pi (excluding -pi). This
    > special inverse tangent uses the sign of x and y to determine the quadrant,
    > and allows for answers in quandrant 2 (-x, +y) and quadrant 3
    > (-x,-y) whereas the standard arctan is restricted to quadrants 1 and 4
    > (range of -pi/2 to +pi/2).
    >
    > There are cases in which ATAN(y/x) does not equal ATAN2(x,y), other than
    > when x = 0. For example, when x = -5 and y =-15, ATAN(-15/-5) = 1.249 and
    > ATAN2(-5,-15) = -1.89
    >
    > I'm not a math expert, but this description seems misleading to me. I
    > suggest a description similar to the C++ ATAN2(x,y) function "The atan2()
    > function computes the arc tangent of y/x, using the signs of the arguments to
    > compute the quadrant of the return value. "
    >
    >


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