CRELCU ( centre, axis, majrad, majaxi, minrad, elipse, ifail )
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  Create an elliptic curve.

Receives:
  KI_vec_centre             centre         --- centre of ellipse
  KI_vec_axis               axis           --- axis direction
  KI_dbl_radius            *majrad         --- major radius
  KI_vec_axis               majaxi         --- major axis
  KI_dbl_radius            *minrad         --- minor radius

Returns:
  KI_tag_curve             *elipse         --- elliptical curve
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_majrad_minrad_mismatch major radius less than minor radius
  KI_majaxi_not_perpn       major axis and axis not perpendicular
  KI_radius_too_large       radius too large

Description:
  An elliptical curve is created. The direction of the major axis must be at
  right angles to the axis of the ellipse. The minor radius must be less than
  or equal to the major radius.

  The curve has a clockwise direction, when viewed along the axis direction.