CalcCFLdt2D.m

function dtcritical=CalcCFLdt2D(UserVar,RunInfo,CtrlVar,MUA,F,u,v)

%
%  CFL   : dt < l/v
%
%

if nargin ==5


    switch lower(CtrlVar.FlowApproximation)


        case 'sstream'

            u=F.ub;
            v=F.vb;


        case 'ssheet'

            u=F.ud ;
            v=F.vd ;


        case 'hybrid'

            u=F.ub+F.ud ;
            v=F.vb+F.vd ;


        otherwise

            error('what case')

    end

end

speed=sqrt(u.*u+v.*v) ;
speed=Nodes2EleMean(MUA.connectivity,speed);

l=sqrt(2*MUA.EleAreas);


dtcritical=min(l./(speed+eps));


if all(speed==0)
    dtcritical=nan;
end

end