<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _log_multivariate_normal_density_spherical(X, means, covars):
 """Compute Gaussian log-density at X for a spherical model."""

    cv = covars.copy()
    if covars.ndim == 1:
        cv = cv[:, np.newaxis]
    if cv.shape[1] == 1:
        cv = np.tile(cv, (1, X.shape[-1]))
    return _log_multivariate_normal_density_diag(X, means, cv)