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These are replies submitted by arashghgood

Dear experts

I try to solve the partial integro-differential equation as following. but I recieved error. I would appreciate it if help me to solve this PIDE.

to have an idea about the equation and boundary conditions you can imagin a tank of water of length l and depth h. eta is considered as initial surface wave. then the PIDE shows the time evolution of the surface wave. (here eta and u(x,t) are the same). inface I try to use approximate solution eta for  initial condition

thank you in advance.



epsilon:= (a/l)^(2/3);

vel:= sqrt(9.81*h)*(1+epsilon/2-3/20*epsilon^2+3/56*epsilon^3);


eta:=h*( epsilon*(sech(X-vel*t))^2#-3/4*epsilon^2*(sech(X-vel*t))^2*(tanh(X-vel*t))^2 + epsilon^3*(5/8*(sech(X-vel*t))^2-101/80*(sech(X-vel*t))^4)*(tanh(X-vel*t))^2

eta:=h*( epsilon*(sech(X-vel*t))^2-3/4*epsilon^2*(sech(X-vel*t))^2*(tanh(X-vel*t))^2 + epsilon^3*(5/8*(sech(X-vel*t))^2-101/80*(sech(X-vel*t))^4)*(tanh(X-vel*t))^2


pdie:= 2*diff(u(x,t),t) + 3*diff(u(x,t),x) * u(x,t) +(1/3.0)*diff(u(x,t),x$3)
      -1/sqrt(Pi)* int(diff(u(x,tau),x)/sqrt(tau), tau= 0..t) = 0;
bounds:= {u(0,t)=0
        , u(10,t)=0
        , u(x,0)= eval(eta,t=0)
        , D[1](u)(0,t)=eval(dx_eta,x=0)#0.2738612788e-1*sech(13.69306394+27.38612788*t)^2*tanh(13.69306394+27.38612788*t)

#Generate IC for D[2](u)(x,0):
bounds:= bounds union{simplify@isolate}(
   convert(value(eval(convert(eval(pdie, {t= 0}), Diff), bounds)), D),

#Convert original PDIE to a true PDE (i.e., without integrals):
pde:= diff(pdie, t);

#Solve PDE system:
psol:= pdsolve(pde, bounds, numeric, optimize=true):
psol:-plot3d(u(x,t), x= 0..10, t= 0..0.2, grid=[150,150],orientation=[-90,0,0],axes=boxed);

Error, (in pdsolve/numeric/plot3d) unable to compute solution for t>HFloat(0.0):
Newton iteration is not converging



as you can see for K=1 the real and complex solutions exist. so K=1 is not interested. I look for (if it is possible) K=K1..K2 where all results (one or more) are imaginary for example. Or K=K3..K4 where all results (one or more) are complex, etc


for example assume that Q and K are real. So Q:=alpha and K=k. and s:=7.44. I attached what I expect to see. I want to have plots like these.



Dear acer

Thnaks for your reply. I think 2D plots are enough to study the relationships. in the cae of (i) (p-K plot) we can fix s.

In this post ( ) I explain how I get this equation by hand. I am also interested in doing this process with maple. could you please take a look at this and help me?


Dear users

is there any idea to solve the issue

this equation can be rewrite like this



maybe it is helpful

@Christian Wolinski 

Thanks a lot for comments on the code.

One more question. Do you have an idea to plot eq and see the zeros of the eq, beyond what I did? and what should I do I I want to study just the real Or just the imaginary section of the K or Q. In  other words, in the case of pure imaginary K, what knid of changes should be done in the code. Is it enought to set the K=0..14*I ?

@Christian Wolinski 

Dear Christian Wolinski 844 , First of all, thank you for your code. It is very interesting for me.

Could you please explain me the last two lines?

map(`@`(evalf, subs), sols, map(`@`(abs, lhs - rhs), EQ));
  fnormal(%, Digits - 4);

@Christian Wolinski 

Note that we aim to solve the eq=0. the term cosh(Q) in the denominator doesn't have a role. I use the denominator to have a clear plot.

could you please explain your post in detail?

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