Coin-or Linear Programming: ClpPlusMinusOneMatrix representation

Question

I'm using Coin-or Linear Programming library. I want to construct a ClpPlusMinusOneMatrix. Its constructor is:

ClpPlusMinusOneMatrix (int numberRows, 
                       int numberColumns, 
                       bool columnOrdered, 
                       const int *indices, 
                       const CoinBigIndex *startPositive, 
                       const CoinBigIndex *startNegative);

It's not exactly clear what startPositive and startNegative are. If it's the same concept as described for another class here, then how does the matrix differentiate +1 and -1 vales?

For example, if I want to implement 1x4 matrix: [1 -1 1 -1]. How does Clp know the value of the last two elements?

#include <coin/ClpPlusMinusOneMatrix.hpp>

int main()
{
        int indices [4] {0, 1, 2, 3}; 
        CoinBigIndex startPositive [2] {0, 4}; 
        CoinBigIndex startNegative [2] {1, 4}; 
        ClpPlusMinusOneMatrix(1, 4, false, indices, startPositive, startNegative);
}

Thanks

Answer 1

If you browse the source code here, you can deduce what startPositve and startNegative are. First, the matrix must be constructed such that all +1 elements must precede all -1 values in a row, if row major, or column, if column major. Then startPositive[i] is simply the element index of the first +1 in row i, if row major, or column i if column major.