docs: def plot_lines(x, fsamps, ax=None, downsample=100, **kwargs):
      """
      Plot function samples as a set of line plots.
  
      Parameters
      ----------
      x: 1D array-like
          x values to plot
  
      fsamps: 2D array-like
          set of functions to plot at each x. As returned by
          :func:`fgivenx.compute_samples`
  
      ax: axes object
          :class:`matplotlib.pyplot.ax` to plot on.
  
      downsample: int, optional
          Reduce the number of samples to a viewable quantity. (Default 100)
  
      any other keywords are passed to :meth:`matplotlib.pyplot.ax.plot`
      """
      if ax is None:
          ax = matplotlib.pyplot.gca()
      if downsample < len(fsamps.T):
          indices = numpy.random.choice(len(fsamps.T), downsample, replace=False)
      else:
          indices = numpy.arange(len(fsamps.T))
      color = kwargs.pop('color', 'k')
      alpha = kwargs.pop('alpha', 0.1)
      for y in fsamps.T[indices]:
          ax.plot(x, y, color=color, alpha=alpha, **kwargs)