Hi tvn,
Am Montag, den 17.01.2011, 14:22 -0800 schrieb tvn:
> I try to solve for 3 variables x y z with 3 equations as below ,
> I am expecting something like z = r1, x = -r1, y = -2*r1 but instead
> get x = y = z = 0 (which trivially valid though not expected). Is
> this because the numbers used too complex (equation 2) and have some
> rounding errors ? if not what's the cause and how to get around it ?
> Thanks
>
>
>
>
> sage version 4.6.1
>
>
> solve([x + 0.106*y + 1.212*z == 0, 3.8759765625*x + 0.04801171875*y +
> 3.972*z == 0, 3.0625*x + 0.09325*y + 3.249*z == 0],[x,y,z])
> [[x == 0, y == 0, z == 0]] #not expected
sage: A = matrix([[1, 0.106, 1.212], [3.8759765625, 0.04801171875,
3.972], [3.0625, 0.09325, 3.249]])
sage: A.rank()
3
Thus (0,0,0) is the unique solution of your system.
Cheers,
Eckhard
>
>
>
>
> Is this due to rounding/precision error because if I replace the 2nd
> equation with another one then it works fine ?
>
>
> solve([x + 0.106*y + 1.212*z == 0, 2.25*x + 0.841*y + 3.932*z == 0,
> 3.0625*x + 0.09325*y + 3.249*z == 0],[x,y,z])
> [[x == -r44, y == -2*r44, z == r44]] #expected
>
>
>
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