如何创建稀疏矩阵作为列表列表？ (C++)

Question

The question is: Is it possible to create a sparse matrix using the following sparse list implementation? In special, using a class template with a class template (SparseList*>)?

I've created a class template named SparseList where I can add elements in whatever index I want.

I'd like to use it to create a SparseMatrix class template. So I tried the following...

//SparseMatrix.h

template <typename T>
class SparseMatrix {
    public:
        SparseMatrix();

    private:
        SparseList<SparseList<T>*> *matrix; 
};

template <typename T>
SparseMatrix<T>::SparseMatrix() {
    matrix = new SparseList<SparseList<T>*>();
}

But when I try to instantiate it on main...

int main() {
    SparseMatrix<int> *matrix;
    matrix = new SparseMatrix<int>(); //without this line it compiled normally.

    return 0;
}

I got the following error...

In file included from src/main.cpp:
SparseMatrix.h:   instantiated from 'SparseMatrix<T>::SparseMatrix() [with T = int]'
main.cpp:   instantiated from here
SparseList.h: error: template argument required for 'struct SparseMatrix'

I'm using NetBeansIDE 6.9.1 with MinGW.

EDIT:

//SparseList.h
template <typename T>
class SparseList {

    template <typename U>
    friend std::ostream & operator<<(std::ostream &output, const SparseList<U> &list);

public:
    SparseList();
    virtual ~SparseList();

    void insert(T &entry, int index);
    T & get(int i);
    int length();

private:
    struct ListNode {
        int index;
        T *entry;
        ListNode *next;
    };

    ListNode *head; //pointer to the first entry in the sparse list.
    int size; //# of entries.
};

I already tested inserts and gets, constructors and destructors, everything in the SparseList. Working fine... =)

Answer 1

Why all the pointers?

This should do the job as your data storage inside your class:

std::map<std::pair<I, I>, T> 

Where I is your index type (eg int ) and T is your number type (eg double).

Or you could just use compressed_matrix from boost::ublas .