## 220 Reputation

2 years, 356 days

## How do I solve the Error, "invalid input...

Maple 2018

Hello.

I wrote some codes for solving equations in a special way. My codes work very fine when my differential system has only one equation.

But when I extend it to a system that has two or more equations, sometimes does not work and I face with error. However, in one system (2 eq) it also works. But it is only a special case. If you want, I can upload it here as well.

I am attaching the maple file containing the error. You can observe it.

By examining many cases, I think that maybe the root of the problem is that I must change my codes in a way that they are for a "system". Indeed, instead of writing codes for each differential equation, I must define a system and write these codes for a system containing some differential equations.
However, I think that the boundary conditions sometimes also may be the root of the error.

I change the attached codes for this purpose, but I failed. I prefer to not present my wrong codes for this purpose.

If it is possible, help me to change my codes.

Thanks a lot.

ERROR.mw

## Tensor summation...

Maple 2018

Hi, I have a problem with tensor calculus. Please guide me.

I have two Tensors B[mu, nu] and A[~mu, ~nu].

Furthermore, I have two mixed tensors as U[~1, mu, nu] and U[~2,mu,nu]

rho, mu, and nu can run from 1 to 2. Hence, A, B, and both Us are 2*2 matrices.

Note that there was only one U, but since it is a mixed tensor, hence I have separated it into two tensors for making it easy.

Now I want to compute the following summation:

U[~rho,mu,nu] U[~alpha,beta,gamma] B[rho,alpha] A[~mu,~beta] A[~nu,~gamma].

Maple must give a number for rho, mu, nu, alpha, beta, and gamma (which can take 1 and 2) and compute "all" possible summations. Since the result will be just "a number", hence I could not use TensorArray.

How can I do it and get a result?

The forms of all tensors are in the attached maple file:
question.mw

## plotting fsolve for given values...

Maple 2018

Hi,

I have two coupled algebraic equations (not differential equations; but only simple algebraic equations; call them "equ1" and "equ2") in which there are three parameters: "x", "y", and "z".

I want to use "fsolve" (Numerical solve) for solving them and then plotting. But since there are three parameters and two equations hence one of the parameters must be given. I want to give a range for "z", for example [2..9], and step size, for example "0.5", such that maple first puts "2" in both equations and solve them numerically and get the values of "x" and "y" and then record them, and then set the value "2.5" for "z" and again repeat the above cycle until the value "z=9". Finally plot both "x" and "y" in terms of "z".

How do I write this?

## 2D Polar Coordinate Plot...

Maple

How can I  get the "phase portrait including vector fields" and several trajectories of the following dynamical system in the polar coordinates (Note that the system is also in polar coordinate)??

## Error in coefficient...

Maple 2019

Hello,

I am trying to extract coefficients of some polynomial expressions but I receive Error.

For example:

>with(Physics):

>Setup(mathematicalnotation = true)

>S := a*(x^2)+b*x+c*(1/(x-h)):

>Coefficients(S, x, 1)

>Error, (in Physics:-Coefficients) unable to compute coeff.

**** Note that if instead of the term (1/(x-h)) we have (1/x), then we get the true result. The error occurs only when we have some extra things in the denominator namely "-h".

Regards

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