Use Complex.ZERO.

This does not change the equals comparison. Note that this will not
detect sign differences, e.g. (0.0, 0.0) == (-0.0, 0.0) and a tolerance
may be required for more robustness.

commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/analysis/solvers/LaguerreSolver.java

@@ -368,7 +368,8 @@ public class LaguerreSolver extends AbstractPolynomialSolver {
                 final Complex denominator = dplus.abs() > dminus.abs() ? dplus : dminus;
                 // Perturb z if denominator is zero, for instance,
                 // p(x) = x^3 + 1, z = 0.
-                if (denominator.equals(Complex.ofCartesian(0.0, 0.0))) {
+                // This uses exact equality to zero. A tolerance may be required here.
+                if (denominator.equals(Complex.ZERO)) {
                     z = z.add(Complex.ofCartesian(absoluteAccuracy, absoluteAccuracy));
                     oldz = Complex.ofCartesian(Double.POSITIVE_INFINITY,
                                        Double.POSITIVE_INFINITY);