[Scilab-users] Re : problem with matrix of polynomials

[Federico Miyara]

Samuel,

Thanks for your answer. Simply being the determinant small doesn't seem 
a problem when using floating point. Probably the bigger problem is the 
presence, somewhere, of very dissimile orders of magnitude.

One curious detail in my example is that the solution of the system when 
adding these lines (input vector and multiplication by the inverse matrix):

V1 = 1;
B = [V1/R1, V1/Z2, 0, 0]';
phi = inv(A) * B;

the denominator of the resulting node potentials in vector phi should be 
of degree 8 but they happen to be just scalars (degree 0) as if the 
coefficients were below %eps

Regards,

Federico


On 09/03/2020 09:36, sgougeon at free.fr wrote:
> Hello Federico,
>
> cond() and rcond() do not accept rationals, but the determinant of A is very close to 0:
> --> det(A)
>   ans  =
>                               
>            3.573D-10
>     ------------------------
>     0.0000027s² +7.433D-10s³
>
> This likely explains that the inversion is not reliable.
>
> Regards
> Samuel
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