code: public static void symmLowerToFull( DMatrixRMaj A )
      {
          if( A.numRows != A.numCols )
              throw new MatrixDimensionException("Must be a square matrix");
  
          final int cols = A.numCols;
  
          for (int row = 0; row < A.numRows; row++) {
              for (int col = row+1; col < cols; col++) {
                  A.data[row*cols+col] = A.data[col*cols+row];
              }
          }
      }
docs: Given a symmetric matrix which is represented by a lower triangular matrix convert it back into
  a full symmetric matrix.
  
  @param A (Input) Lower triangular matrix (Output) symmetric matrix