Added checking for negative number of elements, in case of int overflow. Debugging prints included.

src/TNL/Matrices/Sparse_impl.h

@@ -109,6 +109,20 @@ template< typename Real,
           typename Index >
 void Sparse< Real, Device, Index >::allocateMatrixElements( const IndexType& numberOfMatrixElements )
 {
+    std::cout << "  Allocating matrix elements..." << std::endl;
+   // CHECKING: if the number of matrix elements is larger than the highest number the IndexType can go to?
+   // INT OVERFLOW
+    
+   // CORRECT? ELL stores certain matrices in such a way, which could cause the number of matrix elements 
+   //          to be greater than the maximum value IndexType can store, thus causing int overflow when 
+   //          creating the arrays "values" and "indexes".
+   //   PROBLEM: int can overflow in such a way that it is still positive, thus rendering this assert useless.
+   //       HOW FIX? Do we have to create special conditions for every format in its allocation method? We can't 
+   //                tell from within this method, if numberOfMatrixElements is an overflown value or not.
+   TNL_ASSERT_GE( numberOfMatrixElements, 0, "Number of matrix elements must be non-negative." );
+    
+   std::cout << "  numberOfMatrixElements = " << numberOfMatrixElements << std::endl;
+   
    this->values.setSize( numberOfMatrixElements );
    this->columnIndexes.setSize( numberOfMatrixElements );
 
@@ -118,6 +132,8 @@ void Sparse< Real, Device, Index >::allocateMatrixElements( const IndexType& num
     */
    if( numberOfMatrixElements > 0 )
       this->columnIndexes.setValue( this->columns );
+   
+   std::cout << "->END OF allocateMatrixElements!!!" << std::endl;
 }
 
 template< typename Real,