docs: def correlation_matrix(corrdf, title, **kwargs):
      """Plot image of a matrix correlation.
      Parameters
      ----------
      corrdf: DataFrame
          The matrix correlation to plot.
      title: str
          The matrix title
      Returns
      -------
      str, The resulting image encoded as a string.
      """
      imgdata = BytesIO()
      fig_cor, axes_cor = plt.subplots(1, 1)
      labels = corrdf.columns
      matrix_image = axes_cor.imshow(corrdf, vmin=-1, vmax=1, interpolation="nearest", cmap='bwr')
      plt.title(title, size=18)
      plt.colorbar(matrix_image)
      axes_cor.set_xticks(np.arange(0, corrdf.shape[0], corrdf.shape[0] * 1.0 / len(labels)))
      axes_cor.set_yticks(np.arange(0, corrdf.shape[1], corrdf.shape[1] * 1.0 / len(labels)))
      axes_cor.set_xticklabels(labels, rotation=90)
      axes_cor.set_yticklabels(labels)
  
      matrix_image.figure.savefig(imgdata, bbox_inches='tight')
      imgdata.seek(0)
      result_string = 'data:image/png;base64,' + quote(base64.b64encode(imgdata.getvalue()))
      plt.close(matrix_image.figure)
      return result_string