[math] Complex Tanh for "big" numbers
-------------------------------------
Key: MATH-722
URL: https://issues.apache.org/jira/browse/MATH-722
Project: Commons Math
Issue Type: Bug
Affects Versions: 2.2
Environment: I'm working with Eclipse 3.6.2 on Windows XP, but the bug
is Enviroment independent
Reporter: Juan Barandiaran
Priority: Minor
Hi,
In Complex.java the tanh is computed with the following formula:
tanh(a + bi) = sinh(2a)/(cosh(2a)+cos(2b)) + [sin(2b)/(cosh(2a)+cos(2b))]i
The problem that I'm finding is that as soon as "a" is a "big" number,
both sinh(2a) and cosh(2a) are infinity and then the method tanh returns in
the real part NaN (infinity/infinity) when it should return 1.0.
Wouldn't it be appropiate to add something as in the FastMath library??:
if (real>20.0){
return createComplex(1.0, 0.0);
}
if (real<-20.0){
return createComplex(-1.0, 0.0);
}
Best regards,
JBB
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