= ''' Tangent Approximations ''' =

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== 1 - Actives variables degraded to passive ==
Some active variables are treated as passive (mainly due to non-differentiability characteristics). 

 * ''avmu'', ''avmv'': the vertical eddy viscosity. The turbulent closure scheme ''zdftke'' induces some non-differentiabilities for there variables. They are used in ''dynzdf_imp_tam.F90'' routine.

 * ''uslp'', ''vslp'': the slope of neutral surface (slope of isopycnal surfaces referenced locally) are treated as passive in order to not recomputed them at each step. They are used in ''traldf_iso_tam.F90'' routine.

 * ''wslpi/j'': vertical mixing coefficinet due to lateral mixing. They are used in ''trazdf_imp_tam.F90'' routine.

== 2 - Simplifications ==

*  removal of upstream part of second order centered scheme for ''traadv_cen2_tam.F90''. It introduces 
some non-differentiabilities. Some complementary test must be held to fully implement the second 
order scheme 

* removal of zonal mean lateral diffusive heat and salt transport (''pht_ldf'' and ''pst_ldf'' )

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