matrix([ 1, taylor(x,x,0,1)],
[taylor(y,y,0,1), 1 ]) ^^ -1
matrix([ -1/(y^2-1) , y/(y^2-1) ],
[ y/(y^2-1) , -1/(y^2-1) ])
which is very wrong (it has apparently conflated variables x and y -- depending on the previous session history, it may return a result in x or in y). This happens both with ratmx=false and ratmx=true.
To calculate the correct answer:
Not sure whether this is a problem in the matrix code or the taylor code.