smoothness indicators
s1 = (13.0/12.0)*(v1-2.0*v2+v3)^2 + 0.25*(v1-4.0*v2+3.0*v3)^2
s2 = (13.0/12.0)*(v2-2.0*v3+v4)^2 + 0.25*(v2-v4)^2
s3 = (13.0/12.0)*(v3-2.0*v4+v5)^2 + 0.25*(3.0*v3-4.0*v4+v5)^2