You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: pde15s.m
    path of file: ./repos/chebfun/@chebfun
    
    the code of the file until where you have to start completion: function varargout = pde15s(varargin)
%PDE15S   Solve PDEs using Chebfun.

    
function varargout = pde15s(varargin)
%PDE15S   Solve PDEs using Chebfun.
%
%   UU = PDE15s(PDEFUN, T, U0, BC) where PDEFUN is a handle to a function with
%   arguments u, t, x, and D, T is a vector, U0 is a CHEBFUN or a CHEBMATRIX,
%   and BC is a CHEBOP boundary condition structure will solve the PDE dU/dt =
%   PDEFUN(U, t, x) with the initial condition U0 and boundary conditions BC
%   over the time interval T.
%
%   [TT, UU] = PDE15s(PDEFUN, T, U0, BC) returns also the time chunks TT.
%   If T is a 2-vector these will be given by linspace(T(1), T(2), 51).
%
%   [TT, UU, VV, ...] = PDE15s(...), in the case of a coupled system, will
%   return the quasimatrices UU, VV,... whose columns correspond to each
%   function at the times in the vector TT.
%
%   [TT, UU] = PDE15s(...), in the case of a coupled system, will return the
%   CHEBMATRIX UU, where each row corresponds to a variable at the times TT.
%
%   PDEFUN should take the form @(T, X, U1, U2, ..., UN), where U1, ..., UN are
%   the unknown depend