@@ -263,8 +263,8 @@ For \textbf{EXTOBS}=1 the observed data is read in from one file for all process

"DAMPTYPE" : "2",

\end{verbatim}

Gradients of the L2-norm based data misfit are calculated for each parameter class ($v_p$, $v_s$ and $\rho$) for each shot and summed over all shots and used frequencies. In each iteration raw gradients are stored for each grid point in the folder \textit{grad} in binary format. The order of the values resembles the order in the model files. Their file name include the label given in the input file (GRAD\_FILE), the maximum inversion frequency of this iteration, the parameter class and the iteration number (e.g. \textit{grad/toy\_grad.vp\_200.00Hz\_it6}). Additionally, the conjugate gradients are stored. They are labelled with numbers iteration+1000 (e.g.\textit{grad/toy\_grad.vp\_200.00Hz\_it1006}). \\

It is possible to save additional gradients by including the function \textit{savegrad()} at the required position in the \textit{src/ifos3d.c} source code. This can be useful to look at gradients at single shots or to test a preconditioning function.

Gradients of the L2-norm based data misfit are calculated for each parameter class ($v_p$, $v_s$ and $\rho$) for each shot and summed over all shots and used frequencies. In each iteration raw gradients are stored for each grid point in the folder \textit{grad} in binary format. The order of the values resembles the order in the model files. Their file name include the label given in the input file (GRAD\_FILE), the maximum inversion frequency of this iteration, the parameter class and the iteration number (e.g. \textit{grad/toy\_grad.vp\_200.00Hz\_it6}). Additionally, the conjugate gradients are stored. They are labelled with numbers iteration+2000 (e.g.\textit{grad/toy\_grad.vp\_200.00Hz\_it2006}). \\

It is possible to save additional gradients by including the function \textit{outgrad()} at the required position in the \textit{src/ifos3d.c} source code. This can be useful to look at gradients at single shots or to test a preconditioning function.

\subsubsection*{Gradient preconditioning}

The option \textbf{DAMPTYPE} defines a local preconditioning of the gradients at source and receiver positions as described in section~\ref{sec:preconditioning}. The following options are avalable:\\