-> I'm trying to port some Zeno programs over to BASIC and I'm stuck on the
-> Zeno function ARCTANXY(x,y). According to the Zeno manual,
-> it should be equal to ATN(y/x) when x and y are both non-zero.
-> I created a BASIC function that does that but the results don't match
-> the Zeno output. Does anyone here know exactly what calculation to
-> use for ARCTANXY? TIA
Here's how I usually code it in QBasic.
FUNCTION Ang(X, Y)
SELECT CASE SGN(X)
CASE 1: Ang = ATN(Y / X)
CASE -1: Ang = ATN(Y / X) + PI
CASE ELSE: Ang = SGN(Y) * PI / 2
END SELECT
END FUNCTION
Of course PI has to be pre-defined.
The FUNCTION produces an angle in the range -PI/2 <= Ang < 3*PI/2.
That's the complete circle, but if you want to adjust the range to,
e.g., 0 to 2*PI, you'd have to add a bit of fiddling.
Note that Ang is *not* equal to ATN(Y/X) if X is negative. ATN doesn't
produce the complete circle of values.
dow
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