scalar lambda = 0;

if (mag(lambdaDenominator) < VSMALL)
{ 
    //edge case
    if (mag(lambdaNominator) < VSMALL)
    { 
         // we're very close to the face & moving ~parallel, return lambda explicitly
        if (lambdaDenominator > 0 && lambdaNominator > 0)
        {
            if (lambdaDenominator < lambdaNominator) 
                lambda = 1.1; //needs to be > 1.0, particle stays in cell
            else // travelling along the face   
                lambda = 1.0; // assume we can move to the end position (to machine precision)
        } 
        else if (lambdaDenominator < 0 && lambdaNominator < 0)
        {
            if (lambdaDenominator > lambdaNominator) 
                lambda = 1.1; //needs to be > 1.0, particle stays in cell
            else // travelling along the face   
                lambda = 1.0; // assume we can move to the end position (to machine precision)
                
            
        } 
        else 
        { 
            //moving away from face, needs to be < 0
            lambda = -1.0;
        }
    }
    else
    {
        lamdba = 1.1; // not passing through this face
    }       

} else {
    lambda = lambdaNominator/lambdaDenominator;
}

return lambda;