GNOME Bugzilla – Bug 640344
Incorrect documentation of atan2(y, x)
Last modified: 2011-01-23 23:58:33 UTC
http://projects.gnome.org/gnumeric/doc/gnumeric-ATAN2.shtml and the documentation within (Insert > Function) both descrive atan2 as: b1: angle in radians b2: angle in radians "ATAN2 calculates the arc tangent of the ratio b1/b2..." or Arguments: y: y-coordinate x: x-coordinate However, the inputs appear to be switched! compare: =atan2(0.5,0.7) =atan(0.5/0.7) They should be the same, but instead... =atan2(0.7,0.5) is the one that matches.
I am running http://people.gnome.org/~mortenw/gnumeric/gnumeric-1.10.12-20101125.exe
The description: --------------------------------------- b1: angle in radians b2: angle in radians "ATAN2 calculates the arc tangent of the ratio b1/b2..." --------------------------------------- on the web site is unfortunately outdated. (This is a problem with the website. The documentation in the source that is used to create the html documentation is correct. See for example: http://www.math.concordia.ab.ca/~aguelzow/gnumeric/gnumeric-ATAN2.shtml So the intended description is as in function help browser: ---------------------------------- ATAN2: the arc tangent of the ratio of y and x Arguments: y: y-coordinate x: x-coordinate ATAN2 calculates the direction from the origin to (x,y) as an angle in radians. --------------------------------- And you are absolutely correct that this does not reflect what ATAN2 really calculates. Since this function is intended to be XL compatible we need to check what XL is really calculating to determine whether our function or our documentation is incorrect. On teh web the description of ATAN2 for Excel 2003 and newer is: ------------------------------------- ATan2 function returns the arctangent (in radians) of (x,y) coordinates. ATan2( x-coordinate, y-coordinate ) x-coordinate is the x-coordinate of a point. y-coordinate is the y-coordinate of a point. ------------------------------------- Similarly the ODF description is: ------------------------------------- Summary: Returns the principal value of the arc tangent given a coordinate of two numbers. The angle is returned in radians. Syntax: ATAN2( Number x ; Number y ) Returns: Number Constraints: x<>0 or y<>0 Semantics: Computes the arc tangent of two numbers (the x and y coordinates of a point), in radians. This is similar to ATAN(y/x), but the signs of the two numbers are taken into account so that the result covers the full range from -PI() to +PI(). ATAN2(0;0) is implementation-defined, evaluators may return 0 or an Error. Returns a principal value -PI < result ≤ PI. -------------------------------------- Reassigning to "Documentation" since this is most likely a documentation mistake.
This indeed was a documentation issue. The documentation has been corrected. This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.