From bug-octave-request at bevo dot che dot wisc dot edu Wed Feb 27 11:14:13 2002
Subject: Problem with exp-function
From: Andreas Helms <helms at astro dot physik dot uni-potsdam dot de>
To: bug-octave at bevo dot che dot wisc dot edu
Date: Wed, 27 Feb 2002 18:13:22 +0100


Hello,

I found an unexpected behavior of the exp-function:

octave:8> exp(-700)
ans =  9.8597e-305
octave:9> exp(-750)
ans = 0
octave:10> exp(-730)
error: floating point exception -- trying to return to prompt


I don't know if the floating point exception is a bug in octave or a system 
specific problem (I'm running octave on a TRU64 system). 

The following C++ program 

        #include<math.h>
        #include<iostream>

        int main()

        {

                double x;
                double y;
                x = -700.0;
                y = exp(x);
                cout << "x = " << x << " exp(x) = " << y << endl;

                x = -750.0;
                y = exp(x);
                cout << "x = " << x << " exp(x) = " << y << endl;

                x = -730.0;             
                y = exp(x);
                cout << "x = " << x << " exp(x) = " << y << endl;
                return 0;
        }

gives the output:

        x = -700 exp(x) = 9.85968e-305
        x = -750 exp(x) = 0
        x = -730 exp(x) = 0



     Andreas

        

Lehrstuhl Astrophysik   mailto:helms at astro dot physik dot uni-potsdam dot de
Universitaet Potsdam    http://www.astro.physik.uni-potsdam.de/~helms
D-14469 Potsdam         ftp://ftp.astro.physik.uni-potsdam.de/pub/helms
Phone: +49 331 977 1556  FAX   : +49 331 977 1107



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