[MATH-722] [math] Complex Tanh for "big" numbers

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.2
• Fix Version/s: 3.0
• Labels: patch

Environment

I'm working with Eclipse 3.6.2 on Windows XP, but the bug is Enviroment independent

• Assignee: Sebastien Brisard
• Reporter: Juan Barandiaran
• Created: 09/Dec/11 21:34
• Updated: 24/Mar/12 16:16
• Resolved: 27/Jan/12 07:01

Description

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