Bug introduced in 9.0 or earlier and fixed in 10.3.0
I am trying to get the Green's function of a toy diffusion equation
$$\frac{\partial^2 u(x,t)}{\partial x^2} = \frac{1}{\alpha^2}\frac{\partial u(x,t)}{\partial t}$$
with Mathematica 9. Then solve it by inverse Fourier transform:
u[x_, t_] := InverseFourierTransform[U[k, t], k, x]
D[u[x, t], {x, 2}]
D[D[u[x, t], x], x]
(* 0 *)
(* InverseFourierTransform[-k^2 U[k, t], k, x] *)
But can someone tell me why Out[4]
and Out[5]
are different? Thanks for your kindness.
Trace[D[u[x, t], {x, 2}]]
vs.Trace[D[D[u[x, t], x], x]]
shows this: !Mathematica graphics Mathematically speaking, both should give same result. Maple gives same result as you can see !Mathematica graphics $\endgroup$