[Octave-bug-tracker] [bug #59774] The function acot(x) seems to compute the wrong number for x<0.

[Kai Torben Ohlhus]

Follow-up Comment #2, bug #59774 (project octave):

Rik's post got truncated due to a markup error.

[comment #1 comment #1:]
> Octave is correct, or at least follows other numerical analysis packages.
> 
> On the Wikipedia page you cite, see the section "Relationships between
trigonometric functions and inverse trigonometric functions".  There, you will
find the relationship
> 
> 
> tan (arccot (x)) = 1/x
> 
> 
> Apply arctan() to both sides of the equation and the result is
> 
> 
> arctan (tan (arccot (x))) = arctan (1/x)
> ===
> arccot (x) = arctan (1/x)
> 
> 
> For a test, try
> 
> 
> acot (-1)
> 
> 
> In Octave, Matlab, and Mathematica this returns -pi/4.  Under your scheme
the result is 3/4pi which is different on both the sign and the value.
> 

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