Al86

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5 years, 38 days

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These are replies submitted by Al86

@Preben Alsholm thanks.

BTW do you know why did the collocation code you wrote doesn't seem to work for n:=91 and T:=[seq(0.1..1,0.01)];?

 

Did you try to excute the code in your machine with the change above that I changed?

 

I appreciate your help, but I would like to use collocation method, so I am puzzled why it's get stuck on what I changed.

 

@Preben Alsholm ,I want to use 100 points for the precision on the accuracy of the numerical solution.

My colleague told me that 10 points of sampling isn't enough for what we want to account for.

 

@Preben Alsholm , if I want to use 100 points, I need to change n:=100 and T:=[seq(0..1,0.01)];

 

I changed half an hour ago to n:=91 and T:=[seq(0.1..1,0.01)]; in the code and the code still evaluates on maple 18, is there a way to shorten the computation time?

One of my colleagues told me that something is wrong in the code if it takes that much time to evaluate?

 

@Preben Alsholm how do I find the numerical values of the approximated solution at the collocation points?

 

@Preben Alsholm For my problem I can use the following discretization scheme:

 

If we take time steps x_i = ih, y_j = jh, then:

 

1/h^2(-u_{i,j-1}-u_{i-1,j}+4u_{i,j} - u_{i+1,j} - u_{i,j+1}) = \sqrt(u_{i,j}) + (u_{i+1,j}-u_{i-1,j})^2/(4h^2 * u_{i,j}^{3/2}

 

But how to implement this in maple?

Thanks.

 

@Preben Alsholm , how can I plot the error of this approximated solution?

 

@Carl Love u(x1,x2,x3,x4) satisfies: d^2u/dx1^2+d^2u/dx2^2 = d^2u/dx3^2+d^2u/dx4^2

and u is twice differentiable.

 

@Preben Alsholm , hi, do you happen to know how can I estimate the error in this numerical solution?

 

 

@Preben Alsholm , this is another recursive integral equation which I want to solve numerically, I thought I could do it by using maple.

 

@Axel Vogt t>0, we can also truncate it to t<1.

 

@tomleslie 

Thanks, I appreciate your time you spent on this.

Can you please provide me with the links to the algorithms you talked about? or what did you search in google?

did you search: "methods of solving 2-D inhomogeneous Volterra equations"?

 

@tomleslie 

No need to be so harsh, I made some syntax mistakes, but it seems you got it right:

JT4:=JacobiTheta4((Pi/2)*x, exp((-Pi^2)*s));
JT3:=JacobiTheta3(0, exp((-Pi^2)*r));
h:=0.000065;
INT := v(x,t)=1-h*int(JT4*(1-h*int(JT3*v(1,t-r)^4,r=0..t-s))^4,s=0..t);

 

this is my problem, I want to solve for INT numerically, and I don't have an idea how, I also checked for this integral equation in a handbook of integral equations, but it's not mentioned there.

Do you have some suggestion how to solve this integral equation numerically?

 

@tomleslie 

Ok, here's the attachment:

Solving_numerical_integral.mw

restart;
INT := v(x,t)=1-0.000065*int(JacobiTheta4((Pi/2)*x , exp((-Pi^2)*s))*(1-0.000065*int(JacobiTheta3(0,exp((-Pi^2)*r)
v^4(1,t-r),r=0..t-s)))^4,s=0..t);
 

Error, missing operator or `;`

 

 

 

 

NULL

P.S

I want to numerically solve this equation for v(x,t), I thought of using some numerical integration method, but I seem to first get the above error.

 

Download Solving_numerical_integral.mw

 

@tomleslie 

v(x,t) does depend on x, since JacobiTheta0(1/2 x , i\pi t) = \sum_{m=-\infty}^\infty (-1)^m e^{-m^2\pi^2 t} \cos(m\pi x) , where the cosine depends on x.

I am not sure how to solve this integral equation numerically, so I asked for assitance here, if you can do that superb, if you can't I'll try by myself.

 

@tomleslie 

I tried the errorest option, but it doesn't display the errors in time and space, or of what order are these errors are.

I also need the rate of convergence of this numerical solution.

 

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