pub fn poynting_vector_kernel(
e: &CausalMultiVector<f64>,
b: &CausalMultiVector<f64>,
) -> Result<CausalMultiVector<f64>, PhysicsError>pub fn poynting_vector_kernel(
e: &CausalMultiVector<f64>,
b: &CausalMultiVector<f64>,
) -> Result<CausalMultiVector<f64>, PhysicsError>