added getsubmatrix variant

Author: MarcG-TUE

include/maxplus/algebra/mpmatrix.h

@@ -182,6 +182,8 @@ class Matrix {
 
     [[nodiscard]] Matrix getSubMatrix(const std::list<unsigned int> &indices) const;
 
+    [[nodiscard]] virtual std::shared_ptr<Matrix> getSubMatrixPtr(const std::list<unsigned int> &indices) const;
+
     [[nodiscard]] Matrix getSubMatrixNonSquare(const std::list<unsigned int> &indices) const;
 
     /**

src/algebra/mpmatrix.cc

@@ -608,6 +608,12 @@ Matrix Matrix::getSubMatrix(const std::list<unsigned int> &indices) const {
     return this->getSubMatrix(indices, indices);
 }
 
+std::shared_ptr<Matrix> Matrix::getSubMatrixPtr(const std::list<unsigned int> &indices) const {
+    assert(this->getRows() == this->getCols());
+    return this->getSubMatrixPtr(indices, indices);
+}
+
+
 /**
  * Make sub matrix with indices in list for non-square matrix. The new matrix only keeps the columns
  * of the original matrix with the selected indices.