On Mon, Feb 26, 2018 at 8:52 PM, Juan Luis Varona
<juanluis.var...@gmail.com> wrote:
> In sagemath 7.5, we can use this code:
>
> t=var('t');
> M=matrix(4,[[0,0,5/4,2],[t,0,0,0],[0,1,0,0],[0,0,1,0]]);
> P=charpoly(M);
> P.substitute(x=1)
>
> Then, we get the correct answer
> -13/4*t + 1
>
> However, the same code gives an error with sagemath 8.2.
>
> A workaround that again gives the correct answer with sagemath 8.2 is the
> following:
>
> t=var('t');
> M=matrix(4,[[0,0,5/4,2],[t,0,0,0],[0,1,0,0],[0,0,1,0]]);
> P=charpoly(M);
> y=var('y')
> P.substitute(x=y).substitute(y=1)
>
> What is happening?
>
> Is this a bug or a strange feature of the "x" obtained from charpoly?
>
This works in 7.6 and on cocalc.com:
sage: PR.<x,t> = PolynomialRing(QQ, 2, "x,t")
sage: M=matrix(PR,[[0,0,5/4,2],[t,0,0,0],[0,1,0,0],[0,0,1,0]])
sage: P = M.charpoly()
sage: P(1)
-13/4*t + 1
> Thanks in advance!
>
> Juan Luis Varona
>
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