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Question: How get unknown after substitution by linearization scheme?

Question:How get unknown after substitution by linearization scheme?

salim-barzani 1645 Maple 2024
substitution differential-equations
September 05 2025
0

i did substitution but my result is so different from the author i think he just take the linear term of theta but i didn't do that so how take just linear term of that function and find unknwon , and how afeter replacing eq(12) inside eq(11) we can remove thus exponential and find w? also i think author did a mistake which the equation 12 is theta(x,t) not Q(x,t)

> 

restart
> 

with(PDEtools)
> 

undeclare(prime, quiet)
> 

declare(u(x, t), quiet); declare(U(xi), quiet); declare(V(xi), quiet); declare(theta(x, t), quiet)
> 

pde := diff(u(x, t), `$`(t, 2))-s^2*(diff(u(x, t), `$`(x, 2)))+(2*I)*(diff(u(x, t)*U^2, t))-(2*I)*alpha*s*(diff(u(x, t)*U^2, t))+I*(diff(u(x, t), `$`(x, 2), t))-I*beta*s*(diff(u(x, t), `$`(x, 3)))

diff(diff(u(x, t), t), t)-s^2*(diff(diff(u(x, t), x), x))+(2*I)*(diff(u(x, t), t))*U^2-(2*I)*alpha*s*(diff(u(x, t), t))*U^2+I*(diff(diff(diff(u(x, t), t), x), x))-I*beta*s*(diff(diff(diff(u(x, t), x), x), x))

 (1)
> 

T := u(x, t) = (sqrt(Q)+theta(x, t))*exp(I*(Q^2*epsilon*gamma+Q*q)*t); T1 := U = sqrt(Q)+theta(x, t)

u(x, t) = (Q^(1/2)+theta(x, t))*exp(I*(Q^2*epsilon*gamma+Q*q)*t)

  

U = Q^(1/2)+theta(x, t)

 (2)
> 

P := collect(eval(subs({T, T1}, pde)), exp)/exp(I*(Q^2*gamma*`ε`+Q*q)*t)

diff(diff(theta(x, t), t), t)+(2*I)*(diff(theta(x, t), t))*(Q^2*epsilon*gamma+Q*q)-(Q^(1/2)+theta(x, t))*(Q^2*epsilon*gamma+Q*q)^2-s^2*(diff(diff(theta(x, t), x), x))+(2*I)*(diff(theta(x, t), t)+I*(Q^(1/2)+theta(x, t))*(Q^2*epsilon*gamma+Q*q))*(Q^(1/2)+theta(x, t))^2-(2*I)*alpha*s*(diff(theta(x, t), t)+I*(Q^(1/2)+theta(x, t))*(Q^2*epsilon*gamma+Q*q))*(Q^(1/2)+theta(x, t))^2+I*(diff(diff(diff(theta(x, t), t), x), x)+I*(diff(diff(theta(x, t), x), x))*(Q^2*epsilon*gamma+Q*q))-I*beta*s*(diff(diff(diff(theta(x, t), x), x), x))

 (3)
> 

 

> 

TT := Q = alpha[1]*exp(I*(k*x-t*w))+alpha[2]*exp(-I*(k*x-t*w))

Q = alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w))

 (4)
> 

S := eval(subs(TT, P))

diff(diff(theta(x, t), t), t)+(2*I)*(diff(theta(x, t), t))*(gamma*epsilon*(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^2+(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))*q)-((alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^(1/2)+theta(x, t))*(gamma*epsilon*(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^2+(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))*q)^2-s^2*(diff(diff(theta(x, t), x), x))+(2*I)*(diff(theta(x, t), t)+I*((alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^(1/2)+theta(x, t))*(gamma*epsilon*(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^2+(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))*q))*((alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^(1/2)+theta(x, t))^2-(2*I)*alpha*s*(diff(theta(x, t), t)+I*((alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^(1/2)+theta(x, t))*(gamma*epsilon*(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^2+(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))*q))*((alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^(1/2)+theta(x, t))^2+I*(diff(diff(diff(theta(x, t), t), x), x)+I*(diff(diff(theta(x, t), x), x))*(gamma*epsilon*(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))^2+(alpha[1]*exp((k*x-t*w)*I)+alpha[2]*exp(-I*(k*x-t*w)))*q))-I*beta*s*(diff(diff(diff(theta(x, t), x), x), x))

 (5)

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