I have been thinking about this, would I have to define:
[tex]
C=\frac{\partial}{\partial x}\int Cdx[/tex]
and then define
[tex]
B'=B-\int Cdx[/tex]
to get
[tex]
\frac{\partial A}{\partial t}+\frac{\partial B'}{\partial x}=0[/tex]
and then apply Lax-Wendroff to the above equation?