conatus.expert.lift

conatus.expert.lift(x, basis, n, lam=0, piece=None)

Tau term: x times the polynomial of index N+n of basis (lam=0) or of the ultraspherical C^(lam) basis of the same size and interval (lam >= 1, Chebyshev only): lifting an order-q equation in C^(q) puts its taus in the last q rows of the ultraspherical equation, the classic Olver–Townsend tau (no spurious eigenvalues for dt lap^2-type operators, which T-lifts produce). On a CompoundChebyshev basis piece (required) names the subinterval: mode N_piece + n of that piece (each piece of an order-q equation receives q taus); on a Laguerre basis lam is the derivative level k of L_n^(k) exp(-y/2).

Parameters:

• x (Any)

• basis (Basis)

• n (int)

• lam (int)

• piece (int | None)

Return type:

Expr