There are 2 parameters `NO_SHEAR_MODES`: ```python params.NO_SHEAR_MODES params.oper.NO_SHEAR_MODES ``` See https://foss.heptapod.net/fluiddyn/fluidsim/blob/branch/default/fluidsim/solvers/ns2d/strat/solver.py#L72 The second one should be fine but the first one seems to be buggy. https://foss.heptapod.net/fluiddyn/fluidsim/blob/branch/default/fluidsim/solvers/ns2d/strat/time_stepping.py#L188 The block is useless and `key_fft[0, :] = 0` assumes too much about how the arrays in Fourier space are organized!