API# fourierror.analytical dft() fft() fourierror.numerical dft() fft() fourierror.freq frequencies() fourierror.variable CovVariable CovarianceError concat() covariance_array() covariance_scalar() install_dispatch() install_operand_deferral() uninstall_dispatch() uninstall_operand_deferral() fourierror.data_array CovDataArray covariance_data_array() fourierror.utility validate_input() is_diagonal() construct_output()