acos$m (2) --- calculate inverse cosine                  04/27/83


          | _C_a_l_l_i_n_g _I_n_f_o_r_m_a_t_i_o_n

          |      longreal function acos$m (x)
          |      real x

          |      Library: vswtmath (Subsystem mathematical library)


          | _F_u_n_c_t_i_o_n

          |      This  function  calculates  the  inverse cosine of an angle.
          |      The argument to the function is the cosine of the angle, and
          |      the function returns the measure of the angle,  in  radians.
          |      Arguments  to  the  function  must be in the closed interval
          |      [-1.0, 1.0].  In the case of an error,  the  default  return
          |      value  is  zero.  The condition 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.

          |      This  function  is  intended  to serve as a single precision
          |      function although it returns a double precision result.  The
          |      function has been coded so that any value returned will  not
          |      overflow  or  underflow  a  single  precision floating point
          |      value.  The double precision register  overlaps  the  single
          |      precision register so it is possible to declare and use this
          |      function as simply a "real" function.


          | _I_m_p_l_e_m_e_n_t_a_t_i_o_n

          |      The function is implemented as a rational minimax approxima-
          |      tion  on  a modified argument value.  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

          |      dsqt$m, Primos signl$


          | _S_e_e _A_l_s_o

          |      cos$m (2), dacs$m (2), dsqt$m (2), err$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










            acos$m (2)                    - 1 -                    acos$m (2)