text: """Create coordinates of immersed boundary and save them to file."""
  
  import math
  import numpy
  import pathlib
  
  import petibmpy
  
  
  # Simulation directory.
  simudir = pathlib.Path(__file__).absolute().parents[1]
  
  # Set parameters.
  L, n = 1.0, 60  # Length of the domain and number of cells along a direction
  R = 0.25  # radius of the cylinder
  xc, yc = 0.5, 0.5  # center of the cylinder
  ds = L / n  # approximate distance between two adjacent markers
  N = math.ceil(2 * numpy.pi * R / ds)  # number of segments on boundary
  
  # Create the cylinder coordinates.
  theta = numpy.linspace(0.0, 2 * numpy.pi, num=N + 1)[:-1]
  x, y = xc + R * numpy.cos(theta), yc + R * numpy.sin(theta)
  
  # Save the coordinates into file.
  filepath = simudir / 'cylinder.body'
  petibmpy.write_body(filepath, x, y)
  