vdw_new.cpp
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	#include <iostream>
	#include <Eigen/Core>

	using namespace Eigen;

	#ifndef SCALAR
	#define SCALAR float
	#endif

	#ifndef SIZE
	#define SIZE 10000
	#endif

	#ifndef REPEAT
	#define REPEAT 10000
	#endif

	typedef Matrix<SCALAR, Eigen::Dynamic, 1> Vec;

	using namespace std;

	SCALAR E_VDW(const Vec &interactions1, const Vec &interactions2)
	{
	return (interactions2.cwise()/interactions1)
	.cwise().cube()
	.cwise().square()
	.cwise().square()
	.sum();
	}

	int main()
	{
	//
	// 1 2 3 4 ... (interactions)
	// ka . . . . ...
	// rab . . . . ...
	// energy . . . . ...
	// ... ... ... ... ... ...
	// (variables
	// for
	// interaction)
	//
	Vec interactions1(SIZE), interactions2(SIZE); // SIZE is the number of vdw interactions in our system
	// SetupCalculations()
	SCALAR rab = 1.0;
	interactions1.setConstant(2.4);
	interactions2.setConstant(rab);

	// Energy()
	SCALAR energy = 0.0;
	for (unsigned int i = 0; i<REPEAT; ++i) {
	energy += E_VDW(interactions1, interactions2);
	energy = 1 + 1e-20 i; // prevent compiler from optimizing the loop
	}
	cout << "energy = " << energy << endl;
	}