luby序列的生成函数及其使用

        SAT求解器中search函数的实参是求解发生冲突的限量值。luby函数可以作为序列生成器，序列元素反映一定规律，这样可以使得重启按照指定冲突序列有计划的进行。

先看一下luby函数：

/*
  Finite subsequences of the Luby-sequence:

  0: 1
  1: 1 1 2
  2: 1 1 2 1 1 2 4
  3: 1 1 2 1 1 2 4 1 1 2 1 1 2 4 8
  ...


 */

static double luby(double y, int x){

    // Find the finite subsequence that contains index 'x', and the
    // size of that subsequence:
    int size, seq;
    for (size = 1, seq = 0; size < x+1; seq++, size = 2*size+1);

    while (size-1 != x){
        size = (size-1)>>1;
        seq--;
        x = x % size;
    }

    return pow(y, seq);
}

　　编写如下主函数调用luby函数，程序代码及运行结果如下：

    

#include <cstdlib>
#include <iostream>
#include <cmath>

using namespace std;
static double luby(double y, int x){
 
    // Find the finite subsequence that contains index 'x', and the
    // size of that subsequence:
    int size, seq;
    for (size = 1, seq = 0; size < x+1; seq++, size = 2*size+1);
 
    while (size-1 != x){
        size = (size-1)>>1;
        seq--;
        x = x % size;
    }
 
    return pow(y, seq);
}

int main()
{
    int y1 = 10;
    int x1 = 0;
    double result = 0;
    while(x1 < 20){
        result = luby(y1,x1);
        printf("luby(%-3d,%-2d) = %10.4f\n", y1, x1, result);
        x1++;
    }
    system("color f1");
    system("PAUSE");
    return 0;
}