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. Author manuscript; available in PMC: 2018 Jan 1.
Published in final edited form as: IEEE Trans Med Imaging. 2016 Aug 31;36(1):236–250. doi: 10.1109/TMI.2016.2604568

Fig. 1.

Fig. 1

Theoretical cost estimates of the classic and generalized adjoint approaches compared with the straightforward gradient calculation based on LU decomposition and back substitution.