提高并行矩阵乘法的效率可以采用多种方法，如优化算法、调整计算顺序、并行化等。以下是一种以Java并行化实现的示例代码：

import java.util.concurrent.ForkJoinPool; import java.util.concurrent.RecursiveAction;

public class ParallelMatrixMultiplication extends RecursiveAction { private final int THRESHOLD = 256; private int[][] A, B, C; private int rowStart, rowEnd, colStart, colEnd, size;

public ParallelMatrixMultiplication(int[][] A, int[][] B, int[][] C, int rowStart, int rowEnd, int colStart, int colEnd) {
    this.A = A;
    this.B = B;
    this.C = C;
    this.rowStart = rowStart;
    this.rowEnd = rowEnd;
    this.colStart = colStart;
    this.colEnd = colEnd;
    this.size = A.length;
}

@Override
protected void compute() {
    if ((rowEnd - rowStart) * (colEnd - colStart) <= THRESHOLD) { // 如果矩阵规模小于阈值，则直接串行化计算
        for (int i = rowStart; i < rowEnd; i++) {
            for (int j = colStart; j < colEnd; j++) {
                int sum = 0;
                for (int k = 0; k < size; k++) {
                    sum += A[i][k] * B[k][j];
                }
                C[i][j] = sum;
            }
        }
    } else {
        // 将矩阵分成四块并并行化计算
        int midRow = (rowStart + rowEnd) / 2;
        int midCol = (colStart + colEnd) / 2;
        invokeAll(
                new ParallelMatrixMultiplication(A, B, C, rowStart, midRow, colStart, midCol),
                new ParallelMatrixMultiplication(A, B, C, rowStart, midRow, midCol,