Why is valarray so slow?

Question

I am trying to use valarray since it is much like MATLAB while operating vector and matrices. I first did some performance check and found that valarray cannot achieve the p

Answer 1

I finally got this through using delayed evaluation. The code may be ugly since I am just starting learning these C++ advanced concepts.

Here is the code:

#include 
#include 
#include 
#include "windows.h"

using namespace std;
SYSTEMTIME stime;
LARGE_INTEGER sys_freq;

double gettime_hp();

// To improve the c = a*b (it will generate a temporary first, assigned to 'c' and delete the temporary.
// Which causes the program really slow
// The solution is the expression template and let the compiler to decide when all the expression is known.


// Delayed evaluation
//typedef valarray Vector;
class Vector;

class VecMul
{
    public:
        const Vector& va;
        const Vector& vb;
        //Vector& vc;
        VecMul(const Vector& v1, const Vector& v2): va(v1), vb(v2) {}
        operator Vector();
};

class Vector:public valarray
{
    valarray *p;

    public:
        explicit Vector(int n)
        {
            p = new valarray(n);
        }
        Vector& operator = (const VecMul &m)
        {
            for(int i=0; i

The running result on Visual studio is:

double operator* 41.2031 ms
valarray operator* 43.8407 ms
valarray[i] operator* 42.49 ms