code: def meridian(lat, ell: Ellipsoid = None, deg: bool = True):
      """computes the meridional radius of curvature for the ellipsoid
  
      like Matlab rcurve('meridian', ...)
  
      Parameters
      ----------
      lat : float
          geodetic latitude (degrees)
      ell : Ellipsoid, optional
            reference ellipsoid
      deg : bool, optional
            degrees input/output  (False: radians in/out)
  
      Returns
      -------
      radius: float
          radius of ellipsoid
      """
  
      lat, ell = sanitize(lat, ell, deg)
  
      f1 = ell.semimajor_axis * (1 - ell.eccentricity**2)
      f2 = 1 - (ell.eccentricity * sin(lat)) ** 2
      return f1 / sqrt(f2**3)
  
file_path: pymap3d/src/pymap3d/rcurve.py
imports: from __future__ import annotations
  from .ellipsoid import Ellipsoid
  from .mathfun import cos, sin, sqrt
  from .utils import sanitize
label_desc: Use image node_id 3 for calling a global function with example usage: meridian(lat, ell, deg) and returns: unknown