try operators with fixed input domain

demos/critical_filtering.py

demos/log_normal_wiener_filter.py

demos/paper_demos/cartesian_wiener_filter.py

demos/paper_demos/wiener_filter.py

demos/wiener_filter_via_curvature.py

demos/wiener_filter_via_hamiltonian.py

nifty/domain_tuple.py

nifty/field.py

nifty/library/critical_filter/critical_power_curvature.py

...ormal_wiener_filter/log_normal_wiener_filter_curvature.py

nifty/library/wiener_filter/wiener_filter_curvature.py

nifty/operators/composed_operator/composed_operator.py

nifty/operators/diagonal_operator/diagonal_operator.py

nifty/operators/endomorphic_operator/endomorphic_operator.py

nifty/operators/fft_operator/fft_operator.py

...rs/invertible_operator_mixin/invertible_operator_mixin.py

nifty/operators/laplace_operator/laplace_operator.py

nifty/operators/linear_operator/linear_operator.py

nifty/operators/response_operator/response_operator.py

...operators/smoothing_operator/direct_smoothing_operator.py