function r = m_nthroot(n, A)
  x0 = A / n;
  m  = n - 1;
  while(1)
    x1 = (m*x0 + A./ x0 .^ m) / n;
    if ( abs(x1-x0) < abs(x0 * 1e-9) )
      r = x1;
      return
    endif
    x0 = x1;
  endwhile
endfunction