“…Spectral method, which is well known as a global high accurate numerical approach, has received great attention and has been extensively applied to solving fractional differential equations (FDEs), see, e.g., [4,6,7,11,13,14] and the references therein. Diethelm [5] proved that the Caputo fractional boundary value problem can be reformulated as a Volterra or Fredholm integral equation.…”