Mega Code Archive
Computing an inner product of tuples represented as maps
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#include <map>
#include <iostream>
using namespace std;
int main()
{
const long N = 600000; // Length of tuples x and y
const long S = 10; // Sparseness factor
map<long, double> x, y;
for (long k = 0; 3 * k * S < N; ++k)
x[3 * k * S] = 1.0;
for (long k = 0; 5 * k * S < N; ++k)
y[5 * k * S] = 1.0;
double sum;
map<long, double>::iterator ix, iy;
for (sum = 0.0, ix = x.begin(); ix != x.end(); ++ix) {
long i = ix->first;
iy = y.find(i);
if (iy != y.end())
sum += ix->second * iy->second;
}
cout << sum << endl;
return 0;
}
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