Equation Icon  h1(t;ξ) = u(t;ξ)cos ϕ(t;ξ), h2(t;ξ) = v(t;ξ)cosϕ (t;ξ ), (33 ) h3(t;ξ) = u(t;ξ)sinϕ (t;ξ ), h4(t;ξ) = v(t;ξ)sinϕ (t;ξ),