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?
Thanks in advance!
Juan Luis Varona
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