thrust/examples/max_abs_diff.cu

#include <thrust/inner_product.h>
#include <thrust/functional.h>
#include <thrust/device_vector.h>

#include <iostream>
#include <cmath>

// this example computes the maximum absolute difference 
// between the elements of two vectors

template <typename T>
struct abs_diff : public thrust::binary_function<T,T,T>
{
    __host__ __device__
    T operator()(const T& a, const T& b)
    {
        return fabsf(b - a);
    }
};


int main(void)
{
    thrust::device_vector<float> d_a(4);
    thrust::device_vector<float> d_b(4);

    d_a[0] = 1.0;  d_b[0] = 2.0; 
    d_a[1] = 2.0;  d_b[1] = 4.0;
    d_a[2] = 3.0;  d_b[2] = 3.0;
    d_a[3] = 4.0;  d_b[3] = 0.0;

    // initial value of the reduction
    float init = 0;

    // binary operations
    thrust::maximum<float> binary_op1;
    abs_diff<float>        binary_op2;

    float max_abs_diff = thrust::inner_product(d_a.begin(), d_a.end(), d_b.begin(), init, binary_op1, binary_op2); 

    std::cout << "maximum absolute difference: " << max_abs_diff << std::endl;
    return 0;
}