Bug#499565: basic matrix computations give incorrect results

[John Peterkort]

Sylvestre Ledru wrote:
>> -->A = [ 1 2 0 0 1; 2 0 1 0 2; 3 2 1 -1 4]
>>   A  =
>>
>>      1.    2.    0.    0.    1.
>>      2.    0.    1.    0.    2.  	
>>      3.    2.    1.  - 1.    4.
>>
>> -->R = rref(A)
>>   R  =
>>
>>      1.    0.    0.5     0.    2.
>>      0.    1.  - 0.25    0.    2.776D-17
>>      0.    0.    0.      1.  - 2.
>>
>> -->C = 2 * R
>>   C  =
>>
>>      2.    0.    2.     0.    2.
>>      0.    2.  - 0.5    0.    5.551D-17
>>      0.    0.    0.     2.  - 2.
>>
>> The result of C=2*R is incorrect. C(1,3) should be 1 not 2, C(1,5) should be 4 
>> not 2, and C(3,5) should be -4 not -2.
> After this example, could you try 
> -- > C(1,3)-1
> What is the result ?


-->A = [ 1 2 0 0 1; 2 0 1 0 2; 3 2 1 -1 4]
  A  =

     1.    2.    0.    0.    1.
     2.    0.    1.    0.    2.
     3.    2.    1.  - 1.    4.

-->R = rref(A)
  R  =

     1.    0.    0.5     0.    2.
     0.    1.  - 0.25    0.    2.776D-17
     0.    0.    0.      1.  - 2.

-->C = 2 * R
  C  =

     2.    0.    2.     0.    2.
     0.    2.  - 0.5    0.    5.551D-17
     0.    0.    0.     2.  - 2.

-->C(1,3)-1
  ans  =

   - 1.110D-16

It looks like the display problem occurs at C(1,3), R(1,5) and R(3,5).

-->R(1,5)-1
  ans  =

   - 1.110D-16

-->R(3,5)+1
  ans  =

     1.110D-16


I don't know if this will help you or not, but I downloaded scilab-5.0.1 
directly from The scilab web site.  When I ran it I got the exact same incorrect 
output as I reported in the original bug report.

Also, when running scilab-5.0.1 from the command line I got the following output 
on the terminal:


jack at gig:/data/download/scilab/scilab-5.0.1/bin$ ./scilab
jack at gig:/data/download/scilab/scilab-5.0.1/bin$
(<unknown>:23812): Gtk-WARNING **: Locale not supported by C library.
         Using the fallback 'C' locale.

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64

(<unknown>:23812): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libxfce.so: 
wrong ELF class: ELFCLASS64



  John