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#1
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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
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"Celeste" 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. |
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