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35 lines
1.4 KiB
Markdown
35 lines
1.4 KiB
Markdown
The [_ATAN2](_ATAN2) function returns the radian angle between the positive x-axis of a plane and the point given by the coordinates (x, y).
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## Syntax
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> angle! = [_ATAN2](_ATAN2)(y, x)
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## Parameter(s)
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* y is the vertical axis position (row) as a positive, zero or negative floating point value.
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* x is the horizontal axis position (column) as a positive, zero or negative floating point value.
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## Description
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* The [DOUBLE](DOUBLE) radian angle returned is **positive** for upper row values where y > 0.
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* _ATAN2(y, x) = [ATN](ATN)(y# / x#) when x > 0
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* _ATAN2(y, x) = [ATN](ATN)(y# / x#) + [_PI](_PI) when x < 0
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* _ATAN2(y, x) = [_PI](_PI) / 2 when x = 0
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* The [DOUBLE](DOUBLE) radian angle returned is 0 when x > 0 and [_PI](_PI) when x < 0 where y = 0
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* The [DOUBLE](DOUBLE) radian angle returned is **negative** for lower row values where y < 0.
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* _ATAN2(y, x) = [ATN](ATN)(y# / x#) when x > 0
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* _ATAN2(y, x) = [ATN](ATN)(y# / x#) - [_PI](_PI) when x < 0
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* _ATAN2(y, x) = -[_PI](_PI) / 2 when x = 0
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* _ATAN2(0, 0) is undefined and the function returns 0 instead of a division error.
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## Error(s)
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* With [ATN](ATN)(y / x), x can never be 0 as that would create a Division by Zero [ERROR Codes](ERROR-Codes) 11 or #IND.
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## See Also
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* [ATN](ATN) (arctangent)
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* [_PI](_PI) (QB64 function)
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* [Mathematical Operations](Mathematical-Operations)
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* [Atan2 reference](https://en.wikipedia.org/wiki/Atan2)
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