atan2

[Powersoft]

Dear Forum members,

Is there a working example for the HP Prime to show the atan2(y,x) function?


Thanks.

Jan Kromhout
Hellevoetsluis-NL

[Martin Hepperle]

If you have to roll your own atan2(y,x) function have a look at

http://en.wikipedia.org/wiki/Atan2

Martin

[DrD]

Here is a little atan2(y,x) program especially useful as a subroutine:

Code:


EXPORT atan2(y,x)
BEGIN

// atan2 returns coordinates in correct angle for all four quadrants  
  CASE
    if x==0 AND y==0 then return "undefined"; end;         // x=0, y=0  
    if x>0 then return atan(y/x); end;                     // x>0
    if x<0 AND y>=0 then return atan(y/x)+pi; end;         // x<0, y>=0
    if x==0 AND y>0 then return pi/2; end;                 // x=0, y>0
    if x<0 AND y<=0 then return atan(y/x)-pi; end;         // x<0, y<0
    if x==0 AND y<0 then return -pi/2; end;                // x=0, y<0 
  END;
 
  return;
 
END;

[Helge Gabert]

Don't forget there is also ARG

ARG(x+i*y)=ATAN2(y,x),

and ARG is built-in.

[jte]

(04-11-2015 03:39 AM)Helge Gabert Wrote:  Don't forget there is also ARG

ARG(x+i*y)=ATAN2(y,x),

and ARG is built-in.

I've just tried ARG for a handful of values and have noticed a few minor details that might be worth keeping in mind.

• Both home ARG and CAS arg respect the angle measure setting (radians / degrees).
• Home ARG returns an error for zero while the CAS arg returns 0.0.
• The CAS arg deals with large and small magnitude arguments in a different manner than home ARG does. (With CAS epsilon as 1E-12 and degrees angle measure, CAS arg returns undef for 1E309+i and for 1E-12*i, 90.0 for 1e-12+1e-11*i, and 84.2894068625 for 1.01e-12+1.01e-11*i.)