dsqt$m (2) --- calculate double precision square root    04/27/83


          | _C_a_l_l_i_n_g _I_n_f_o_r_m_a_t_i_o_n

          |      longreal function dsqt$m (x)
          |      longreal x

          |      Library: vswtmath (Subsystem mathematical library)


          | _F_u_n_c_t_i_o_n

          |      This  function  calculates  the  square  root  of  a  double
          |      precision floating point value.  Attempts to take the square
          |      root of negative values will result in an error.  The condi-
          |      tion SWT_MATH_ERROR$ is signalled if there  is  an  argument
          |      error.   An  on-unit  can  be  established to deal with this
          |      error; the SWT Math Library contains a default handler named
          |      'err$m' which the user may utilize.  The default  return  in
          |      this  case  will be the square root of the absolute value of
          |      the argument.


          | _I_m_p_l_e_m_e_n_t_a_t_i_o_n

          |      The algorithm involved is based  on  Newton's  approximation
          |      method  with  an  initial multiplicative approximation.  The
          |      argument is scaled to within the range [0.5, 2.0)  and  then
          |      the algorithm is iterated to a solution.  It is adapted from
          |      the  algorithm  given  in  the  book _S_o_f_t_w_a_r_e _M_a_n_u_a_l _f_o_r _t_h_e
          |      _E_l_e_m_e_n_t_a_r_y _F_u_n_c_t_i_o_n_s by William Waite and William Cody,  Jr.
          |      (Prentice-Hall, 1980).


          | _C_a_l_l_s

          |      Primos signl$


          | _S_e_e _A_l_s_o

          |      err$m (2), sqrt$m (2),
          |      _S_W_T _M_a_t_h _L_i_b_r_a_r_y _U_s_e_r_'_s _G_u_i_d_e

















            dsqt$m (2)                    - 1 -                    dsqt$m (2)