On Tue, Nov 16, 2010 at 8:13 AM, SoTaNeZ <[email protected]> wrote:
> Hi all.
>
> I got this exception while executin numpy.linalg.solve(a,b) being:
>
> a = array([[ 1.00000000e+000, -4.19430400e+006, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, -2.47845883e-119,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> -2.68435456e+008, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, -3.38813179e-021, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, -4.09600000e+003,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> -2.56000000e+002, 0.00000000e+000, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, -7.20575940e+016, 0.00000000e+000],
> [ 1.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, 0.00000000e+000,
> 0.00000000e+000, 0.00000000e+000, -1.56250000e-002],
> [ 1.00000000e+000, 1.00000000e+000, 1.00000000e+000,
> 1.00000000e+000, 1.00000000e+000, 1.00000000e+000,
> 1.00000000e+000, 1.00000000e+000, 1.00000000e+000]])
>
> b = array([0, 0, 0, 0, 0, 0, 0, 0, 1])
>
> I guess some numbers in a are too big or too small, aren't they?
some eigenvalues are very close to zero
>>> np.linalg.eigh(a)[0]
array([ -2.87298335e+00, -1.60293723e-16, -3.43582743e-17,
-1.24477525e-32, -1.84567471e-33, 3.95359079e-33,
8.81541828e-18, 4.09615908e-16, 4.87298335e+00])
if you need to get a robust solution, you could use lstsq, but whether
the solution makes sense will depend on your application (I guess it
should be equivalent to using the pinv)
>>> np.linalg.lstsq(a,b)
(array([ -5.91579259e-08, 2.21469552e-14, 2.31028827e-10,
-2.06502900e-16, 2.31028892e-10, 5.95746983e-08,
1.51994027e-05, -8.20980166e-25, 2.31042993e-10]),
array([], dtype=float64), 5, array([ 7.20575940e+16,
2.68435456e+08, 4.19430411e+06,
4.09600024e+03, 2.56003891e+02, 2.30353618e+00,
1.30462749e+00, 1.03982867e-02, 1.95397635e-10]))
Josef
>
> Thanks,
> David.
>
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