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## Re: apparently wrong description of 'arg' function in octave-3.0.5

**From**: |
Ben Abbott |

**Subject**: |
Re: apparently wrong description of 'arg' function in octave-3.0.5 |

**Date**: |
Sun, 17 Apr 2011 10:54:26 -0400 |

On Apr 17, 2011, at 8:55 AM, Sergei Steshenko wrote:
>* Hello,*
>* *
>* in octave-3.0.5 'help arg' produces:*
>* *
>* "*
>* -- Mapping Function: arg (Z)*
>* -- Mapping Function: angle (Z)*
>* Compute the argument of Z, defined as THETA = `atan (Y/X)'. in*
>* radians.*
>* ".*
>* *
>* According to Wiki and my memories from school:*
>* *
>* http://en.wikipedia.org/wiki/Inverse_trigonometric_functions :*
>* *
>* arctangent y = arctan x x = tan y all real numbers −π/2 < *
>* y < π/2 −90° < y < 90°*
>* *
>* , i.e. the ranges equivalently are:*
>* *
>* −π/2 < y < π/2 −90° < y < 90°*
>* .*
>* *
>* The above ranges are insufficient for complex numbers - the range in*
>* radians should be either*
>* *
>* -pi .. pi*
>* *
>* or*
>* *
>* 0 .. 2 * pi.*
>* *
>* In reality the 'arg' function works correctly:*
>* *
>* "*
>* octave:23> 180 / pi * arg(-1 + 0.01i)*
>* ans = 179.43*
>* octave:24> 180 / pi * arg(-1 - 0.01i)*
>* ans = -179.43*
>* ",*
>* *
>* i.e. it implements -pi .. pi (-180 .. 180 degrees) range - opposed to*
>* what its built-in help message says (because of 'atan' and it's*
>* -pi/2 .. pi/2 range).*
>* *
>* Is the description fixed in later 'octave' versions ?*
The current sources include ...
-- Mapping Function: arg (Z)
-- Mapping Function: angle (Z)
Compute the argument of Z, defined as, THETA = `atan2 (Y, X)', in
radians.
Ben