Why does transform_reduce give a different result than transform & reduce?

I tested some pull code and found that transform_reduce gives a slightly different computation result which completely confused me.

Here's an example test code: (for calculating the sum (exp (x)))

It has been executed and launched in VS2012 + CUDA 6.0

#include <iostream>
#include <cmath>
#include <thrust/device_vector.h>

using namespace std;

template <typename T>
struct exponential
{
    __host__ __device__
        T operator()(const T& x) const { 
            return exp(x);
    }
};

void main() {
    thrust::device_vector<double> f(7), g(7);
    f[0]=0.0; f[1]=1.0; f[2]=2.0; f[3]=3.0; f[4]=5.0; f[5]=5.0; f[6]=5.0;
    double d = thrust::transform_reduce(f.begin(), f.end(), exponential<double>(), 0, thrust::plus<double>());
    cout<<"transform_reduce result: " d<<endl;

    thrust::transform(f.begin(), f.end(), g.begin(), exponential<double>());
    double e = thrust::reduce(g.begin(), g.end());
    cout<<"transform+reduce result: "<<e;

}

      

        
        
        
      

    

The way out I got was that

transform_reduce result: 474
transform+reduce result: 476.432

      

        
        
        
      

    

The correct value should be 476.432 I don't know what happened in transform_reduce. This not only gives an integer but also the wrong answer. Doesn't mean transform_reduce should be the same as transform + reduce?

Please help me explain what happened ...