code: def gridlines(ax, scale, multiple=None, horizontal_kwargs=None,
                left_kwargs=None, right_kwargs=None, **kwargs):
      
  
      if 'linewidth' not in kwargs:
          kwargs["linewidth"] = 0.5
      if 'linestyle' not in kwargs:
          kwargs["linestyle"] = ':'
      horizontal_kwargs = merge_dicts(kwargs, horizontal_kwargs)
      left_kwargs = merge_dicts(kwargs, left_kwargs)
      right_kwargs = merge_dicts(kwargs, right_kwargs)
      if not multiple:
          multiple = 1.
      ## Draw grid-lines
      # Parallel to horizontal axis
      for i in arange(0, scale, multiple):
          horizontal_line(ax, scale, i, **horizontal_kwargs)
      # Parallel to left and right axes
      for i in arange(0, scale + multiple, multiple):
          left_parallel_line(ax, scale, i, **left_kwargs)
          right_parallel_line(ax, scale, i, **right_kwargs)
      return ax
docs: Plots grid lines excluding boundary.
  
      Parameters
      ----------
      ax: Matplotlib AxesSubplot, None
          The subplot to draw on.
      scale: float
          Simplex scale size.
      multiple: float, None
          Specifies which inner gridelines to draw. For example, if scale=30 and
          multiple=6, only 5 inner gridlines will be drawn.
      horizontal_kwargs: dict, None
          Any kwargs to pass through to matplotlib for horizontal gridlines
      left_kwargs: dict, None
          Any kwargs to pass through to matplotlib for left parallel gridlines
      right_kwargs: dict, None
          Any kwargs to pass through to matplotlib for right parallel gridlines
      kwargs:
          Any kwargs to pass through to matplotlib, if not using
          horizontal_kwargs, left_kwargs, or right_kwargs