CIGAL Reference Manual, Chapter 3 (Functions): atan

Atan -- Calculate the arc tangent of a variable or a ratio

usage: tgtvarb = atan(srcvarb)
or: tgtvarb = atan(svarb1,svarb2)

The second form calculates the arc tangent of the ratio of the two arguments. This is done using the C library function ATAN2 instead of ATAN.

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