diff.h

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#ifndef __SABLIB_DIFF_H__
#define __SABLIB_DIFF_H__
 
#include <Eigen/Eigen>
 
namespace sablib {

enum class Dir {
    RowWise,   
    ColumnWise 
};

template <typename Derived>
const typename Derived::PlainObject
Diff(const Eigen::MatrixBase<Derived> & m0, const int n = 1, const Dir dir = Dir::RowWise)
{
    typename Derived::PlainObject m = m0;
    int rows = m.rows(), columns = m.cols();
 
    if(dir == Dir::ColumnWise){
        for(int i = 0; i < n ; i++){
            int col_counts = columns - i - 1;
            m.leftCols(col_counts) = m.block(0, 1, rows, col_counts) - m.leftCols(col_counts);
        }
 
        return m.leftCols(columns - n);
    }
    else{
        for(int i = 0; i < n ; i++){
            int row_counts = rows - i - 1;
            m.topRows(row_counts) = m.block(1, 0, row_counts, columns) - m.topRows(row_counts);
        }
 
        return m.topRows(rows - n);
    }
}

template <typename Derived>
const typename Derived::PlainObject
Diff(const Eigen::SparseMatrixBase<Derived> & m0, const int n = 1, const Dir dir = Dir::RowWise)
{
    typename Derived::PlainObject m = m0;
 
    if(dir == Dir::ColumnWise){
        for(int i = 0; i < n; i++){
            m = (m.rightCols(m.cols() - 1) - m.leftCols(m.cols() - 1)).eval();
        }
    }
    else{
        for(int i = 0; i < n; i++){
            m = (m.bottomRows(m.rows() - 1) - m.topRows(m.rows() - 1)).eval();
        }
    }
 
    return m;
}
 
}; // namespace sablib
 
#endif // __SABLIB_DIFF_H__