Example 2: Example 3.2.4 (p. 101 of Peressini, Sullivan, Uhl)

> f := X -> X[1]^2 + a^2 * X[2]^2;
gradf := X -> vector( [ 2*X[1], 2*a^2*X[2] ] );
Hf := X -> matrix( [ [ 2, 0 ], [ 0, 2*a^2 ] ] );
a := 6.;
x0 := vector( [ evalf( a/sqrt(1+a^2) ), evalf( 1/a/sqrt(1+a^2) ) ] );
a := 6.;
tol := 10.^(-5);
N := 15;

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