ClearMatrix := proc(    A :: Matrix,
                      tol :: numeric  )
   local m, n, i, j;
   m, n := LinearAlgebra:-Dimension(A);
   for i from 1 to m do
      for j from 1 to n do
         if abs(A[i,j]) < tol then
            A[i,j] := 0
         end if
      end do
   end do;
   return A;
end proc;