hi friends

I encountered a problem and I can not draw the plot of this code

> sol := fsolve({diff(S, x) = 0, diff(S, y) = 0}, {x, y});

> with(VectorCalculus);

> with(linalg);

> s1 := evalf(subs(sol, linalg[grad](S, [x, y])));

> with(VectorCalculus);

> with(LinearAlgebra);

> s2 := evalf(subs(sol, linalg[hessian](S, [x, y]))); pmp0 := [x-subs(sol, x), y-subs(sol, y)]; sapprox := s0+evalm(`&*`(`&*`(transpose(pmp0), s2), pmp0));

> with(Statistics);

>

> with(stats); statevalf[icdf, chisquare[4]](.95);

> with(VectorCalculus);

> with(plottools);

> with(plots);

> with(linalg); ellips := {seq(stats*([statevalf[icdf, chisquare[4]]])(c) = sapprox, c = [.5, .95, .999])};

> plots(ellips(x, y), x = 950 .. 1000, y = 700 .. 750, grid = [50, 50], view = [950 .. 1000, 700 .. 750]);

can you helpe me?Thank you