Specifies how strong previous iteration steps are weighted in the modified Broyden scheme. For WC large, the last iteration step is weighted most. When starting with bad moments it is useful to cancel the stored Jacobi matrix after some iterations to let the calculation forget its history (delete file MIXM). You can also choose an arbitrary negative value for WC. In this case, WC is adjusted internally according to the inverse root mean square difference of the components of the mixed vector.