ETKI ignores timestepper

[odunbar]

Purpose

ETKI (and EKI) adapt to the timestep by dividing the noise covariance by the timestep

EnsembleKalmanProcesses.jl/src/EnsembleTransformKalmanInversion.jl

Line 113 in fb45f75

scaled_obs_noise_cov = ekp.obs_noise_cov / ekp.Δt[end]

unfortunately, unlike in EKI, ETKI does not use this quantity, instead it uses an internally stored inverse covariance.

Solution

Simply multiply the stored inverse covariance in etki_update by the timestep to pass this effect on.