如何减去两个稀疏向量

Question

我刚接触SparseVector。我想减去两个SparseVectors，并返回结果为SparseVector。

Vector和SparseVector的区别是什么?

我试图从定义函数开始，需要两个SparseVector，但没有得到任何帮助我!

import java.awt.Point;
import java.util.HashMap;
import cern.colt.list.DoubleArrayList;
import cern.colt.matrix.impl.SparseDoubleMatrix1D;
public class SparseVector extends SparseDoubleMatrix1D {
    public SparseVector(int size) {
        super(size);
    }
    public SparseVector(double[] values) {
        super(values);
    }
    public  SparseVector subtract(SparseVector v1, SparseVector v2) {
        // TODO: How to implement it?
    }
}

Answer 1

似乎没有必要创建自定义实现。请考虑下面的例子:

import cern.colt.matrix.impl.SparseDoubleMatrix1D;
import cern.jet.math.Functions;
// …
final SparseDoubleMatrix1D aMatrix = new SparseDoubleMatrix1D(new double[] { 3.0 });
final SparseDoubleMatrix1D bMatrix = new SparseDoubleMatrix1D(new double[] { 1.0 });
aMatrix.assign(bMatrix, Functions.minus);
// aMatrix is the result.
System.out.println(aMatrix);

请参考cern.jet.math.Functions类。

<标题> 自定义实现

注意静态方法可能是冗余的。

import cern.colt.matrix.impl.SparseDoubleMatrix1D;
import cern.jet.math.Functions;
final class SparseVector extends SparseDoubleMatrix1D {
    public SparseVector(int size) {
        super(size);
    }
    public SparseVector(double[] values) {
        super(values);
    }
    /**
     * Subtract otherVector from this vector.
     * The result is stored in this vector.
     * @param otherVector other vector
     * @return this vector
     */
    public SparseVector subtract(SparseVector otherVector) {
        assign(otherVector, Functions.minus);
        return this;
    }
    public static SparseVector subtract(SparseVector x, SparseVector y) {
        final SparseVector result = new SparseVector(x.toArray());
        result.subtract(y);
        return result;
    }
}

的例子:

final SparseVector aVector = new SparseVector(new double[] { 3.0 });
final SparseVector bVector = new SparseVector(new double[] { 1.0 });
aVector.subtract(bVector);
// aVector is the result.
System.out.println(aVector);