## is it possible to change ODE to PDE?...

is it possible to change ODE to PDE?

the ODE has diff(a(t),t) and diff(b(t),t)

how to convert to diff(t, a), diff(t, b) ?

## PDEtools build ...

What's wrong here?

restart; with(PDEtools); PDE2 := diff(u(x, y, t), t\$2) = diff(u(x, y, t), x\$2)+diff(u(x, y, t), y\$2); IBC2s := u(x, 0, t) = 0, u(x, 2, t) = 0, u(0, y, t) = 0, u(4, y, t) = 0, u(x, y, 0) = (.1*(-x^2+4*x))*(-y^2+2*y), (D[3](u))(x, y, 0) = 0; Sol2 := pdsolve({IBC2s, PDE2}); build(Sol2);

Error, invalid input: PDEtools:-build uses a 1st argument, ANS (of type {`=`, PDESolStruc}), which is mis

## Problem aplying the chain rule with dchange...

I have a problem using dchange when my variable depend on two (or more variables) and I would like to apply the chain rule.

For example, when I use the command

I would expect something like

But I get an error saying that the number of new variables and transformation equations must be the same.

Any idea how I could solve it?

Thanls a lot for your help.

## Can I numerically solve a PDE set with one initial...

I am wondering if I can use MAPLE to solve PDE set with one initial value problem for "q" and a boundary condition problem for "p". "q" need to be integrated over time, and for each time step, after updating "q", I need to solve poisson equation for "p":

diff(q(x,y,t),t)=-diff(p(x,y,t),x)*diff(q(x,y,t),y)/cos(xy)+diff(p(x,y,t),y)*diff(q(x,y,t),x)/cos(y)+b*cos(y)^2*diff(p(x,y,t),x)+F(x,y)

diff(p(x,y,t),x,x)+diff(p(x,y,t),y,y)+c(y)*p(x,y,t)=q(x,y,t)

IC: q(x,y,0)=q0(x,y)

BC: periodic in x, second type BC in y.

Many Thanks!

Wanying

## Solving a non linear system of PDE...

I want to solve the following non linear PDE

SS := [diff(u(x, y, t), t)-0.625e-1*(diff(u(x, y, t), x, x)+diff(u(x, y, t), y, y))-6*(diff(u(x, y, t)*(diff(v(x, y, t), x)), x)+diff(u(x, y, t)*(diff(v(x, y, t), y)), y)) - 2*(u(x, y, t))(1-u(x, y, t))=0, diff(v(x, y, t), t)-(diff(v(x, y, t), x, x))-(diff(v(x, y, t), y, y))+16*v(x, y, t) -u(x, y, t)=0]

when i use the command

sol := pdsolve(SS, [u, v], singsol = false)

maple give the error message

Error, (in pdsolve) found the independent variables {t, x, y} also present in the names of the functions of the system []

## How do I express bc for PDE...

I have a PDE with boundary conditions, from a NASA paper.  I always seem to have problems expressing the bc.

PDE := diff(u(x, t), t) = (1/4)*exp(2)*exp(-u(x, t))*(diff(diff(u(x, t), x), x))/(x^2+2);

The initial/boundary conditions are

@t=0, u(x, t) = 2-2*ln(-x^2+2)

@x=0, diff(u(x,t),x)=0  ## this is the bc I have problem expressing

@x=1, u(x,t) = 2+ln(1+t)

The exact solution given in the paper:

2 + ln(1+t) - 2*ln(2-x^2)

I tried

ics := u(x, 0) = 2*(1-ln(2-x^2));

bcs := D[1](u(0,t))=0, u(1,t)=2+ln(1+t);

PDEtools[Solve]([PDE,ics,bcs]); ## no solution

How do I do this?

Tom Dean

## How do I obtain a simplified system automatically...

HI everyone,

As can be seen from the attached file, the first three equations of Eq. (5) will render some of the other equations (and other terms) redundant. How can I obtain a simplified system automatically?

Thanks.

Pdesample.mw

## Does TWS command of Maple solves system of ODEs ?...

Dear all

I am trying to solve system of ODEs by TWS command for traveling wave solution, but an error is showing. When I enter sinlge ODE or PDE the command does not show any error. Why it is showing error for system of ODEs ?

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## PDETools Invariants Command Not Recognizing Rotati...

Hi, I'm trying to use Maple to construct some examples of symmetry solutions for certain nonlinear PDE's.  As a warm up, however, I'm working through the commands just for the heat equation in 3d: u[t]-u[x,x]-u[y,y]-u[z,z]=0

I've gotten Maple to produce both determining equations for the symmetry infinitesimal generators via the DeterminingPDE command.  I've also gotten the command Infinitesimals to work too.

However, when I next use PDETools Invariants command, it correctly outputs invariants for most of the generator output of Infinitesimals EXCEPT it won't output anything for the simple rotation generators yd[x]-xd[y].  It will, however, output invariants if the rotation is between an independent and the dependent coordinate.

An example:
with(PDETools)
S:=[_xi[x]=y, _xi[y]=-x, _eta[u]=0]
Invariants(S,u(x,y))

*Above returns nothing, But if you instead have _xi[x]=x and _xi[y]=y then it returns the right invariants.

## A problem about the "Infinitesimals" in pdetools...

There is an example in the help of maple, that is to solve the symmetries of the equation ut=uxx using the order "Infinitesimals".

But the result i can't understand.

I solved by hand and find  _eta[u](x, t, u)=cu+b(x,t), where b(x,t) is a solution of the ut=uxx.

While in maple, b is only two exponential function which are also the solution of ut=uxx.

why?

## How I can use Differential Algebra package to obta...

Dear All

I need to reduce system of differential equation system into triangular system which I came to know can be done using Maple package "DifferentialAlgebra", but I do not know how to use this package for triangularization.

The differential system is DetSys derived from  some PDE:

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 (1)
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 (3)
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 (4)
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 (5)
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Regards

Hello, I am using PDEtools to evaluate an equation but got system inconsistent in respect of a parameter used after the command map(pdsolve). I am afraid the result sebsequently given may not be correct, did I do something wrong?

Thanks.

test.mw

## Problem with coefficients in PDEtools...

hi,

i want to compute the determining PDE system satisfied by the infinitesimals, such as the KdV equation.

but i have a problem, if i use the command

DeterminingPDE(PDE1, integrabilityconditions = false, split = false)

i can get the coefficients of independent objects, but u[t] exists.

i want to replace u[t] by (-u[x]u-u[x,x,x]), then extract the coefficients.

but i can't collect the coefficients.

my code:

with(PDEtools, DeterminingPDE, declare, diff_table, casesplit, InfinitesimalGenerator, Infinitesimals, SymmetryTest, ReducedForm, FromJet, ToJet);

declare(u(x, t));

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

PDE1 := U[]*U[x]+U[t]+U[x, x, x] = 0;

DetSys := DeterminingPDE(PDE1, integrabilityconditions = false, split = false);
detsys := FromJet(DetSys, u(x, t), differentiationnotation = diff);
pd1 := subs(U[t] = -U[]*U[x]-U[x, x, x], detsys); #u[t]->(-u[x]u-u[x,x,x])
pd2 := ToJet(pd1, [u(x, t)]);

how do i collect the coefficients?

help!

## Equating partial derivative to zero...

In PDEtools, suppose to I wish assign zero value to certain first order partial derivative such that higher order derivatives automatically vanish in subsequent excutions, how I can do that?

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 (1)

Suppose we wish following derivative equal to zero,

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 (2)

If we use ":=" for value assignment we will get error. Under above assuption how can we make following derivatives zero?

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 (3)
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## The dchange command returns zero...

Hello Maple primers

I am trying to do a coordinate transformation which involves a number of partial derivatives. I turned to the PDETools[dchange] to accomplish this but it will just return 0 when run through.

The problem is as such. First two functions are defined which contain a lot of "stuff". Then the forward and reverse transformations are defined between the coordinates; and finally the transformation is done.

del_1:=Diff(Y,r1,r1)+2/r1*(Diff(Y,r1)) + Diff(Y,r2,r2)+2/r2*(Diff(Y,r2))+2*(Diff(Y,r3,r3))+4/r3*(Diff(Y,r3))+((r1^2-r2^2+r3^2)/(r1*r3))*(Diff(Y,r1,r3))+(r2^2-r1^2+r3^2)/(r2*r3)*(Diff(Y,r2,r3)):

del_2:=Diff(Y,r1,r1)+2/r1*(Diff(Y,r1))+(r1^2-r2^2+r3^2)/(r1*r3)*Diff(Y,r1,r3)+Diff(Y,r2,r2)+2/r2*(Diff(Y,r2))+(-r1^2+r2^2+r3^2)/(r2*r3)*(Diff(Y,r2,r3))+4/r3*(Diff(Y,r3))+2*(Diff(Y,r3,r3)):

#Forward transformation

R1:=0.5*(v)+0.25*(w):
R2:=0.5*(u)+0.25*(w):
R3:=0.5*(u)+0.5*(v):

tr:={r1=R1,r2=R2,r3=R3}:

#Reverse transformation
rR1:=(-r1+r2+r3):
rR2:=(r1-r2+r3):
rR3:=2*(r1+r2-r3):

rtr:={u=rR1,v=rR2,w=rR3}:
nv:={u,v,w}:
AA:=simplify(del_1+del_2);
PDEtools[dchange](tr,AA,nv,rtr);

This will return zero. Is there something obvious I am missing here? I have used the dchange tool before in a similar manner and it has worked without issue.

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