public double EVAL(
UnivariatePolynomial p, double lowerBound, double upperBound, double fl, double fu) {
// System.out.println( "EVAL on (" + lowerBound + "," + upperBound + ") |-> (" + fl + "," + fu +
// ")" );
double m = (lowerBound + upperBound) / 2.0;
double r = (upperBound - lowerBound) / 2.0;
// System.out.println( "(m,r)=("+m+","+r+")" );
if (upperBound - lowerBound < EPSILON) {
// System.out.println( "epsilon reached" );
// prevent infinite loop (e.g. for non-squarefree polynomials)
if (fl * fu < 0.0) return m;
else return m; // java.lang.Double.NaN;
}
// test for exclusion predicate: no real root in (m-r,m+r)
UnivariatePolynomial t = p.shift(m);
// System.out.println( "Taylor exp. of f(x-" + m + "): " + t );
double fm = t.getCoeff(0);
double ta[] = t.getCoeffs();
ta[0] = -Math.abs(ta[0]);
for (int i = 1; i < ta.length; ++i) ta[i] = Math.abs(ta[i]);
if (0.0 > new UnivariatePolynomial(ta).evaluateAt(r)) return java.lang.Double.NaN;
// System.out.println( "Exclusion predicate false" );
// test for inclusion predicate: exactly one real root in (m-r,m+r)
UnivariatePolynomial t_der = p.derive().shift(m);
// System.out.println( "Taylor exp. of f'(x-" + m + "): " + t_der );
double ta_der[] = t_der.getCoeffs();
ta_der[0] = -Math.abs(ta_der[0]);
for (int i = 1; i < ta_der.length; ++i) ta_der[i] = Math.abs(ta_der[i]);
if (fl * fu <= 0.0 && 0.0 > new UnivariatePolynomial(ta_der).evaluateAt(r))
return bisect(p, lowerBound, upperBound, fl, fu);
// System.out.println( "Inclusion predicate false" ); System.out.println();
// bisect
double result_left = EVAL(p, lowerBound, m, fl, fm);
if (!java.lang.Double.isNaN(result_left)) return result_left;
else return EVAL(p, m, upperBound, fm, fu);
}
