Old method for generating coords, used on original analysis
        of yeast data. Included to reproduce yeast result from paper.
        Reason for difference - switched to using spectral embedding
        method provided by scikit-learn (mainly because it spreads 
        points over a sphere, rather than a half sphere, so looks
        better plotted). Uses a different Laplacian matrix.

def spectral_embedding_(self, n):
        """
        Old method for generating coords, used on original analysis
        of yeast data. Included to reproduce yeast result from paper.
        Reason for difference - switched to using spectral embedding
        method provided by scikit-learn (mainly because it spreads 
        points over a sphere, rather than a half sphere, so looks
        better plotted). Uses a different Laplacian matrix.
        """
        aff = self._affinity.copy()
        aff.flat[::aff.shape[0]+1] = 0
        laplacian = laplace(aff)
        decomp = eigen(laplacian)
        return CoordinateMatrix(normalise_rows(decomp.vecs[:,:n]))