Bug#499565: basic matrix computations give incorrect results
Sylvestre Ledru
sylvestre.ledru at inria.fr
Mon Sep 22 12:45:50 UTC 2008
> -->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 ?
We believe this might be a display issues (ie the internal value is OK
but the display is wrong...).
This used to occur with old version of gfortran.
Sylvestre
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