def _init_structures(self, data, subjects):
        """Initializes data structures for SRM and preprocess the data.


        Parameters
        ----------
        data : list of 2D arrays, element i has shape=[voxels_i, samples]
            Each element in the list contains the fMRI data of one subject.

        subjects : int
            The total number of subjects in `data`.


        Returns
        -------
        x : list of array, element i has shape=[voxels_i, samples]
            Demeaned data for each subject.

        mu : list of array, element i has shape=[voxels_i]
            Voxel means over samples, per subject.

        rho2 : array, shape=[subjects]
            Noise variance :math:`\\rho^2` per subject.

        trace_xtx : array, shape=[subjects]
            The squared Frobenius norm of the demeaned data in `x`.
        """
        x = []
        mu = []
        rho2 = np.zeros(subjects)

        trace_xtx = np.zeros(subjects)
        for subject in range(subjects):
            mu.append(np.mean(data[subject], 1))
            rho2[subject] = 1
            trace_xtx[subject] = np.sum(data[subject] ** 2)
            x.append(data[subject] - mu[subject][:, np.newaxis])

        return x, mu, rho2, trace_xtx
Initializes data structures for SRM and preprocess the data.


        Parameters
        ----------
        data : list of 2D arrays, element i has shape=[voxels_i, samples]
            Each element in the list contains the fMRI data of one subject.

        subjects : int
            The total number of subjects in `data`.


        Returns
        -------
        x : list of array, element i has shape=[voxels_i, samples]
            Demeaned data for each subject.

        mu : list of array, element i has shape=[voxels_i]
            Voxel means over samples, per subject.

        rho2 : array, shape=[subjects]
            Noise variance :math:`\rho^2` per subject.

        trace_xtx : array, shape=[subjects]
            The squared Frobenius norm of the demeaned data in `x`.
        
hypertools/_externals/srm.py