[TurbJet]

Hello,

I have one simple question about OpenFoam matrix class.

In it's definition, the function 'allocate' says:

void Foam::Matrix<Form, Type>::allocate()
{
    if (n_ && m_)
    {
        v_ = new Type*[n_];
        v_[0] = new Type[n_*m_];

        for (register label i=1; i<n_; i++)
        {
            v_[i] = v_[i-1] + m_;
        }
    }
}

What baffles me is that since v_ is a pointer to a pointer, it supposes to be a 2D array. However, what about this part:

v_[0] = new Type[n_*m_];

? It seems only v_[0] saves the entire matrix, namely the matrix is stored in a 1D-form. But why it still do this :

v_ = new Type*[n_];

?

Why not doing something like:

v_ = new Type * [n_];
for(i=0; i<n_;++i)
    v_[i] = new Type [m_];

Thanks ahead !

[GerhardHolzinger]

My guess is that two memory allocations

v_ = new Type*[n_];
v_[0] = new Type[n_*m_];

were deemed more efficient than doing n+1 allocations

v_ = new Type * [n_];
for(i=0; i<n_;++i)
    v_[i] = new Type [m_];

The way it is implemented

void Foam::Matrix<Form, Type>::allocate()
{
    if (n_ && m_)
    {
        v_ = new Type*[n_];
        v_[0] = new Type[n_*m_];

        for (register label i=1; i<n_; i++)
        {
            v_[i] = v_[i-1] + m_;
        }
    }
}

you get pretty much the look&feel of a 2D array.

[TurbJet]

Originally Posted by GerhardHolzinger

My guess is that two memory allocations

v_ = new Type*[n_];
v_[0] = new Type[n_*m_];

were deemed more efficient than doing n+1 allocations

v_ = new Type * [n_];
for(i=0; i<n_;++i)
    v_[i] = new Type [m_];

The way it is implemented

void Foam::Matrix<Form, Type>::allocate()
{
    if (n_ && m_)
    {
        v_ = new Type*[n_];
        v_[0] = new Type[n_*m_];

        for (register label i=1; i<n_; i++)
        {
            v_[i] = v_[i-1] + m_;
        }
    }
}

you get pretty much the look&feel of a 2D array.

I still don't get it. With this one

v_[0] = new Type[n_*m_];

doesn't it mean all the elements will be saved in v[0][i] ? If so, why doesn't it just declare a 1D array to save the entire matrix?