docs: @Override
      public boolean setA(DMatrixRBlock A) {
          if( A.numRows < A.numCols )
              throw new IllegalArgumentException("Number of rows must be more than or equal to the number of columns.  " +
                      "Can't solve an underdetermined system.");
  
          if( !decomposer.decompose(A))
              return false;
  
          this.QR = decomposer.getQR();
  
          return true;
      }