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forward models are ignored and only contributions from the regularization and 
forward models are ignored and only contributions from the regularization and 
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crossgradient term are used. 
crossgradient term are used. 
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\end{methoddesc} 
\end{methoddesc} 
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\section{Gradient calculation}\label{chapter:ref:inversion cost function:gradient} 
\section{Gradient calculation}\label{chapter:ref:inversion cost function:gradient} 
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In this section we briefly discuss the calculation of the gradient and the Hessian operator. 
In this section we briefly discuss the calculation of the gradient and the Hessian operator. 