How to calculate the sum of a vector without using loop or std::accumulate()?

Question

I'm trying to implement an Euclidean vector for my programming assignment. I need to overload operator* to provide dot product calculation for two vectors with arbitrary same dimension. As 3D vector for example:

Vector<3> v1, v2; //two 3D vectors.

double dotProduct = v1 * v2;

The value of dotProduct should be v1[0]*v2[0]+v1[1]*v2[1]+v1[2]*v2[2]

So, my problem is how to get this value without using any explicit loop and std::accumulate() operation in numeric.h header file? Because those are forbidden in this assignment.

P.S. I may use functor(self defined) together with STL algorithm.

1) Do you know that the operands will always be three-dimensional? 2) What is a Vector? — Robᵩ
– Robᵩ, Commented Nov 3, 2012 at 2:51
As you've written dotProduct = v1[0]*v2[0]+v1[1]*v2[1]+v1[2]*v2[2], it appears to me that you have an idea of how to approach this. What have you tried and where exactly are you stuck? — Anthony Burleigh
– Anthony Burleigh, Commented Nov 3, 2012 at 2:56
There is no <numeric.h>, only <numeric>. Your answer is on this page. (Hint: the dot product is a type of what?) — GManNickG
– GManNickG, Commented Nov 3, 2012 at 3:00
What you're trying to compute is normally called an inner product. Searching existing algorithms with that mind might be fruitful. — Jerry Coffin
– Jerry Coffin, Commented Nov 3, 2012 at 3:04
std::for_each may serve well when using builtin loops isn't permitted. — Stephen Niedzielski
– Stephen Niedzielski, Commented Nov 3, 2012 at 3:13

Jerry Coffin · Accepted Answer · 2012-11-03 03:14:25Z

2

If you really want to avoid explicit loops and algorithms in general (not just std::accumulate), you could use std::valarrays instead:

std::valarray<double> a;
std::valarray<double> b;

// code to put data in a and b goes here

double dotProduct = (a * b).sum();

I've used double as the type here, but you can (of course) use whatever type makes sense for the data/situation you're dealing with.

answered Nov 3, 2012 at 3:14

Jerry Coffin

494k83 gold badges656 silver badges1.2k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Lorenz · Accepted Answer · 2016-03-16 16:03:03Z

1

You can use std::inner_product, see http://en.cppreference.com/w/cpp/algorithm/inner_product

double dotProduct = std::inner_product(v1.begin(), v1.end(), v2.begin());

answered Mar 16, 2016 at 16:03

Lorenz

1065 bronze badges

Comments

Robᵩ · Accepted Answer · 2012-11-03 03:06:58Z

0

If you can't use explicit loops, perhaps your teacher is asking you to use recursion.

template<int N>
int VectorSum(const Vector<N>& v1, const Vector<N>& v2, int m) {
  if(m) return v1[m]*v2[m] + VectorSum(v1, v2, m-1);
  return v1[0]*v2[0];
}

template<int N>
int operator+(const Vector<N>& v1, const Vector<N>& v2) {
  return VectorSum(v1, v2, N-1);
}

answered Nov 3, 2012 at 3:06

Robᵩ

170k20 gold badges251 silver badges323 bronze badges

Comments

lovaya · Accepted Answer · 2012-11-03 12:08:20Z

0

I happened to read a text about it， so I copy it for you. may be it's introduced in the book :C++ Templates: The Complete Guide.

#include <iostream>

template<int DIM,typename T>
struct DotProduct {
    static T execute(const T v1[],const T v2[]);
};
template<int DIM,typename T>
T DotProduct<DIM,T>::execute(const T v1[],const T v2[]) {
    return v1[0]*v2[0] + DotProduct<DIM-1,T>::execute(v1+1,v2+1);
};

template<typename T>
struct DotProduct<1,T> {
    static T execute(const T v1[],const T v2[]);
};

template<typename T>
T DotProduct<1,T>::execute(const T v1[],const T v2[]) {
    return v1[0]*v2[0];
};

int main()
{
    int v1[] = {1,2,3}; 
    int v2[] = {4,5,6};
    int r2 = DotProduct<3,int>::execute(v1,v2);
    std::cout << r2 << std::endl;
    return 0;
}

answered Nov 3, 2012 at 12:08

lovaya

4633 silver badges3 bronze badges

1 Comment

JackHuVandy Over a year ago

A nice example for using template and recursion! Thanks a lot!

Collectives™ on Stack Overflow

How to calculate the sum of a vector without using loop or std::accumulate()?

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related