Example 1: Problem #4 (p. 129 of Peressini, Sullivan, Uhl)

> f := X -> 2*X[1]^4+X[2]^2-4*X[1]*X[2]+5*X[2];
gradf := X -> vector( [ 8*X[1]^3-4*X[2], 2*X[2]-4*X[1]+5 ] );
Hf := X -> matrix( [ [ 24*X[1]^2, -4 ], [ -4, 2 ] ] );
x0 := vector( [ 0., 0.] );
tol := 10.^(-5);
N := 20;

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