[Numpy-discussion] Error in tanh for large complex argument

Pauli Virtanen pav at iki.fi
Fri Jan 28 05:30:00 EST 2011


Fri, 28 Jan 2011 11:25:19 +0100, Mark Bakker wrote:
> I'll file a ticket.
> 
> Incidentally, if tanh(z) is simply programmed as
> 
> (1.0 - exp(-2.0*z)) / (1.0 + exp(-2.0*z))

This will overflow as z -> -\infty. The solution is probably to use a 
different expression for Re(z) < 0, and to check how other libraries do 
this in case the above still misses something.

	Pauli




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