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Question: An error about subs()

Question:An error about subs()

zhuxian 60 Maple
typesetting subs pdetools
October 21 2017
0

 

restart

with(PDEtools)

declare(u(x, t))

` u`(x, t)*`will now be displayed as`*u

 (1)

U := diff_table(u(x, t))

char := eta(x, t, U[])-U[x]-2*U[t]

eta(x, t, u(x, t))-(diff(u(x, t), x))-2*(diff(u(x, t), t))

 (2)

       

pde := U[x]+U[x, x]

diff(u(x, t), x)+diff(diff(u(x, t), x), x)

 (3)

tp1 := subs(U[] = char, pde)

diff(eta(x, t, u(x, t))-(diff(u(x, t), x))-2*(diff(u(x, t), t)), x)+diff(diff(eta(x, t, u(x, t))-(diff(u(x, t), x))-2*(diff(u(x, t), t)), x), x)

(4)

 

Just as the result above, I can't interpret why the last term of the formula (4) is (2)_xx.

 

Is ther a bug, or just because I made a mistake somewhere???

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Thanks!

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