Re: Sparse matrix problem

[Dmitri A. Sergatskov]

On 1/3/07, David Bateman <address@hidden> wrote:
> address@hidden wrote:
>
> > [1+i 2-i] ./ [0 0-i]
> >
> > gives under Octave
> >
> > [NaN + NaNi     1 +   2i]
> >

> >
> > Michael.
> >
> No as that is a problem with the underlying C++ complex class and not
> octave at all.. Try the attached test program, which for me using g++
> 4.0.1 returns
>
> (1+i) / (0 + 0i) : (nan,nan)
> (1+i) / 0 : (nan,nan)
> 1 / 0 : inf

Try to compile the test program with optimization on. On my computer
(gcc version 4.1.1 20061011 (Red Hat 4.1.1-30))
address@hidden test1]$ g++ -O0 test.cc -o test
test.cc: In function 'int main()':
test.cc:10: warning: division by zero in '1.0e+0 / 0.'
address@hidden test1]$ ./test
(1+i) / (0 + 0i) : (nan,nan)
(1+i) / 0 : (nan,nan)
1 / 0 : inf
address@hidden test1]$ g++ -O2 test.cc -o test
test.cc: In function 'int main()':
test.cc:10: warning: division by zero in '1.0e+0 / 0.'
address@hidden test1]$ ./test
(1+i) / (0 + 0i) : (inf,inf)
(1+i) / 0 : (inf,inf)
1 / 0 : inf
(The same result with -O1)
In octave I get:

octave:1> [1+i 2-i] ./ 0
warning: division by zero
ans =

  Inf + Infi   Inf - Infi

octave:2> [1+i 2-i] ./ [0, i]
ans =

  NaN - NaNi    -1 -   2i

Since Octave is compiled with -O2 this test program does not seems to
be a representative example ...

Sincerely,

Dmitri.
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