(Pi/2. ) != (90.0 DegToRad)

From: Kathrin Stoerig <Kathrin.Stoerig_at_cern.ch>
Date: Thu, 21 Dec 2006 12:31:16 +0100

Hello,

I have been working with some trigonometric functions of the
"TMath"-Class when I discovered a peculiar behaviour of ROOT v5.0.12e.
I have appended a stand-alone piece of my code. The comments at the end show my output when compiling or interpreting. While interpreting with Cint, everything is okay, but when I compile it, the following comparison is astonishing to me:

"Double_t phi=90.0*TMath::DegToRad();

 if (phi==TMath::Pi()/2.0) returns "false",  while if(phi==TMath::PiOver2()) returns true?! "

Much more interesting is the fact, that:
"Double_t phi=90.0*TMath::DegToRad();

cout<<phi<<endl;
 if (phi==TMath::Pi()/2.0) now returns "true" - instead of "cout" e.g. an empty "for"-loop is possible and still returns "true", a variable declaration as "Int_t a=5" returns "false" and "Double_t b=TMath::Cos(5.)" returns "true" again.

Any ideas?
As you can see in my code, I tried a lot of possibilities (casting the numbers to doubles, updating ROOT to version 5.0.14 etc.) without success. Please tell me whats wrong or how to prevent this infelicitous situation.

Best regards,
Kathrin Stoerig

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Kathrin Störig

II.Physikalisches Institut

Universitaet Goettingen                                      Telefon: 

+49 551 39 12214

Friedrich-Hund Platz 1 D-37077 Goettingen Telefax: +49 551 39 4493

Kathrin.Stoerig_at_phys.uni-goettingen.de
<mailto:Kathrin.Stoerig_at_phys.uni-goettingen.de>

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Received on Thu Dec 21 2006 - 12:31:30 MET