## 30 Reputation

2 years, 138 days

## Problem with Solving a PDE...

Maple 2021

Hi Everyone,

I intend to find the invariants of a 2nd-order Tensor using the representation of the rotational group as an Infinitesimal generator. However, maple does not seem to find the correct invariants $\tr \mathbf{a}$, $\tr \mathbf{a}^2$, $\tr \mathbf{a}^3$. Maple only returns an empty set. I can't seem to figure out why that is the case.

Here is my code

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 (1)
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 (4)

Any input would be appreciated!

## Expanding Derivatives in Equations...

Maple 2021

Hi Everyone,

ich have a question, that is probably rather trivial. I am currently doing some calculations with the differential geometry package. (I know the Physics package was recommended, however, the DG package seems more appropriate for my purposes after having a look through the Physics help page)

My goal is to substitute a functional expression into equations derived in curvilinear (spherical and helical) coordinates. my problem now is that maple won't expand the differentials of the expressions I have substituted.

I hope the answer isn't too trivial. Although I assume it will be :)

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 (1)

Defining the Metric Tensor and Calculating the Connection Coefficients

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 (1.3)

Defining the PDF as a Tensor (Metric) Density

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 (2.1)
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Convective Operator

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 (3.1)
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In particular, the last line should simplify quite a bit when expanding derivatives.

## Covariant Derivative of a Tensor Density...

Maple

Hi Everyone,

surely my question has a simple answer, however, I am a bit stumped. I need to calculate field equations for which I need to take the covariant derivative of a tensor density. This yields additional "Christoffel-terms" in the usual manner.

For mathematical details see e.g. (https://math.stackexchange.com/questions/2267059/covariant-derivative-of-tensor-densities)

(I hope it's ok to link resources from another forum)

My problem is that I can't seem to find a command to define a tensor density in the Differential Geometry package. I can only obtain Metric densities through the "MetricDensity" command. However, this command does not create a tensor density in the usual manner.

One workaround might be to substitute the Metric Density from the command mentioned above into the covariant derivative after expanding in terms of the Christoffel-symbols.

Any input would be appreciated.

## Lie Symmetries of ODE-Systems for a give...

Maple

Hi everyone,

I'm new to using Maple and I've got a question concerning the calculation of the Lie Symmetries of an ODE. Basically, I want to us the method described in this paper: https://doi.org/10.1063/1.3097304 in order to find a perturbative solution to a system of first oder ODE's.

I thus need a special form of the generator. However I can't quite figure out the notation from the examples provided in the maple helt. I also can't figure out why I can't calculate the general form of the Symmetries using the following code:

restart;
with(PDEtools);
with(DEtools);
Imp := 2*diff(y(x), x)*y(x)/A(x) - diff(y(x), x) - diff(A(x), x)*(y(x)/A(x))^2 - C_p*diff(A(x), x) - eta(x)*lambda(x)*sqrt(A(x)*pi)/4*(y(x)/A(x) - 1)^2 = 0;
Conti := diff(y(x), x) - 2*sqrt(A(x)*pi)*beta(x)*(1 - H + C/A(x)) = 0
Cons := diff(eta(x), x) = 0

sys := {Cons, Conti, Imp};
DepVars = {A(x), eta(x), y(x)};
deteqs := DeterminingPDE(sys);


Help or a link to some more examples would be much appreciated.

Regards,

Johannes

## Error When using DeterminingPDE...

Maple

Good Afternoon,

I'm relatively new to using Maple and I have encountered a problem that I don't seem to be able to figure out myself.

I am trying to calculate the determining equations, and subsequently the infinitesimals of an underdetermined set of PDE's. However, I keep getting the error message

"Error, (in PDEtools:-ToJet) incorrect use of the dependent variable name(s) [R, p, u, v, w], as indexed function names in: {w[](R[z]*v[y]+v[z]), w[](R[z]*w[y]+w[z])}"

restart;
with(PDEtools);
with(DEtools);
declare(u(y, z));
u(y, z) will now be displayed as u

declare(v(y, z));
v(y, z) will now be displayed as v

declare(w(y, z));
w(y, z) will now be displayed as w

declare(p(y, z));
p(y, z) will now be displayed as p

declare(R(z));
R(z) will now be displayed as R

Conti := diff(u(y, z), y) + u(y, z)/(y - R(z)) + diff(w(y, z), z) + diff(R(z), z)*diff(w(y, z), y) = 0;
NSU := v(y, z)^2/(y - R(z)) - diff(p(y, z), y) = 0;
NSV := ((u(y, z)*diff(v(y, z), y) + u(y, z)*v(y, z)/(y - R(z)) + w(y, z)(diff(v(y, z), z) + diff(R(z), z)*diff(v(y, z), y))) + (-diff(v(y, z), y)/(y - R(z)) - diff(v(y, z), y, y) + v(y, z)/(y - R(z))^2)) + diff(R(z), z)*diff(w(y, z), y) = 0;
NSW := u(y, z)*diff(w(y, z), z) + w(y, z)(diff(w(y, z), z) + diff(R(z), z)*diff(w(y, z), y)) + diff(p(y, z), z) + diff(R(z), z)*diff(p(y, z), y) - diff(w(y, z), y)/(y - R(z)) - diff(w(y, z), y, y) - diff(R(z), z)*diff(w(y, z), y) = 0;
sys := [Conti, NSU, NSV, NSW];
deteqs := Infinitesimals(sys);
Error, (in PDEtools:-ToJet) incorrect use of the dependent variable name(s) [R, p, u, v, w], as indexed function names in: {w[](R[z]*v[y]+v[z]), w[](R[z]*w[y]+w[z])}


The Maple Worksheet is also provided below. All help is greatly appreciated.

Regards,

Johannes

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