code: def _create_dct_matrix(self):
          
          self.s2dct = numpy.zeros((self.mfcc_size, self.filter_bank_size))
          for i in range(0, self.mfcc_size):
              freq = numpy.pi * float(i) / self.filter_bank_size
              self.s2dct[i] = numpy.cos(freq * numpy.arange(0.5, 0.5 + self.filter_bank_size, 1.0, 'float64'))
          self.s2dct[:, 0] *= 0.5
          self.s2dct = self.s2dct.transpose()
docs: Create the not-quite-DCT matrix as used by Sphinx,
          and store it in ```self.s2dct```.