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  Java bug with ATAN2  (Read 635 times)
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Offline jmguillemette
« Posted 2013-12-31 14:48:49 »

Ok.. i think i just tripped across a java bug in the Math.atan2(x,y) operation.

Atan2 should return the following results.

X   Y         Atan2
1   1         0.785398163
-1   1         2.35619449
1   -1         -0.785398163
-1   -1         -2.35619449

but if you run Atan2 with 1, -1 you dont get -0.78.. instead you get 2.356!

Not sure if this is true for all versions of java.. can anyone try this out and see what you get?


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Offline jmguillemette
« Reply #1 - Posted 2013-12-31 14:53:07 »

just tried the same code on another machine and the function works as expected.
So its likely this bug is isolated to a specific release of java.

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Offline jmguillemette
« Reply #2 - Posted 2013-12-31 14:57:48 »

arg.. i may have found my cause.. (face to palm)
in Java atan2 is y, x instead of x,y

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Offline matheus23

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« Reply #3 - Posted 2013-12-31 14:57:54 »

But you are aware, that it's
atan2(y, x)

Either you turned that around, or the implementation turned that around.

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Offline jmguillemette
« Reply #4 - Posted 2013-12-31 15:00:46 »

matheus your right on the money..

in my math i was calculating the angle so i could do some math against its specific coordinates.

i looked up the atan2 operation and everywhere i looked it was standardized on x, y
but the javadoc for Math.atan2 is y,x and i missed it .

of course i dont find that till i post up here (after being stuck for a day and a bit, trying to figure out why my math was not working )

such is the way.. back to happy coding now i guess.


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