java - 在Java中寻找多项式的根

Question

我需要找到 Legendre polynomial 的(近似数值)解.我尝试了几个 Java 库，但没有一个有我要找的东西(最接近的是 commons-math，它甚至有用于在 Laguerre solver 中查找解决方案的代码，但它没有公开方法)。是否有现有的解决方案，或者我是否需要实现自己的解决方案？

Answer 1

您可以使用 EJML (高效的 Java 矩阵库)。

请在下面找到相同的示例。

public class PolynomialRootFinder {

    /**
     * <p>
     * Given a set of polynomial coefficients, compute the roots of the polynomial.  Depending on
     * the polynomial being considered the roots may contain complex number.  When complex numbers are
     * present they will come in pairs of complex conjugates.
     * </p>
     *
     * @param coefficients Coefficients of the polynomial.
     * @return The roots of the polynomial
     */
    public static Complex64F[] findRoots(double... coefficients) {
        int N = coefficients.length-1;

        // Construct the companion matrix
        DenseMatrix64F c = new DenseMatrix64F(N,N);

        double a = coefficients[N];
        for( int i = 0; i < N; i++ ) {
            c.set(i,N-1,-coefficients[i]/a);
        }
        for( int i = 1; i < N; i++ ) {
            c.set(i,i-1,1);
        }

        // Use generalized eigenvalue decomposition to find the roots
        EigenDecomposition<DenseMatrix64F> evd =  DecompositionFactory.eigGeneral(N, false);

        evd.decompose(c);

        Complex64F[] roots = new Complex64F[N];

        for( int i = 0; i < N; i++ ) {
            roots[i] = evd.getEigenvalue(i);
        }

        return roots;
    }
}