RE: Confusing definition of atan2

Paul,

You are correct. The Verilog-2005 LRM makes the same mixup.
Although, as you say, it is mathematically correct, I will file an issue
with P1800 to correct it there.

Shalom

> -----Original Message-----
> From: owner-verilog-ams@server.eda.org [mailto:owner-verilog-
> ams@server.eda.org] On Behalf Of Paul Floyd
> Sent: Thursday, April 19, 2007 1:16 PM
> To: verilog-ams
> Subject: Confusing definition of atan2
> 
> Hi
> 
> In section 4.2.2 of the LRM, atan2 is defined as
> 
> atan2(x, y) Arc-tangent of x/y
> 
> Mathematically, this is correct, but to me it seems more conventional
> to
> reverse the order of x and y. When I started learning trigonometry, I
> was taught that tan is opposite over adjacent, or tan(t) = y/x, for a
> triangle like
> 
>    /|
>   / |
>  /  | y
> /t  |
> -----
>  x
> 
> For the LRM definition, the triangle would have to be
> 
>    /|
>   / |
>  /  | x
> /t  |
> -----
>   y
> 
> which I find a bit confusing.
> 
> In C, atan2 is declared as double atan2(double y, double x);
> 
> Regards
> Paul
> --
> Dr Paul Floyd
> Mentor Graphics Corporation
> 
> 
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