.. _step3_section:


STEP 3 : Add the transverce velocity *v* 
========================================


Modify the source file in order to solve the y-component equation of the momentum to obtain the *v* component of the velocity vector. 


Firstly, write down the corresponding equation.

Check the best position in the conservative vector for this unknown (what is the actual unknown asscociated to this equation in conservative form?).

Also check the files **INITGAZ.DAT** as well as the subroutines :   **initgaz, prim, ecritplot, green_flux**.



.. hint ::
 In 1D a transverse velocity a constant field of v **does not change** the solution of the shock tube problem : it acts as a passive scalar !