## 220 Reputation

2 years, 344 days

## Wrong identity solve...

Maple

Hello.

I have two terms r and g as:

r := x*(diff(theta(t), t))^2+y*(diff(varphi(t), t))^2;

g := (4*(f+T))*(diff(theta(t), t))^2+u*(diff(varphi(t), t))^2;

Now I want to equate these as r=g and find x and y

As we see, x and y must be 4*(f+T), and u, respectively.

I used "solve" and also "solve(identity....)" and "isolate" and also "eliminate" but all of them failed and I face another solution in which x has y !!!! for example, see the result for "solve(r = g, {x, y})"

However, I can use "coeff" and get the result, but in this case, indeed I write the solution, not maple, while I have this expectation that maple does these and give me the result:

coeff(r,(diff(theta(t), t))^2)=coeff(g,(diff(theta(t), t))^2);

coeff(r,(diff(varphi(t), t))^2)=coeff(g,(diff(varphi(t), t))^2);

This example is a simple one; in complicated cases, I must write more codes, for example, perhaps I must use isolate as well.... For this reason, I want to find a short and applicable code.

## arrows do not appear in system of DE...

Maple

Hi,

Happy new year.

I have a problem, if it is possible please guide me.

I want to add "arrows=small/curve/...." (i.e. vector fields) to the following maple's example, but unfortanutley it does not work (see the green code and run it ....).

It is not important to me that I use phaseportrait or DEplot or dfieldplot, I just want to show arrows in any "scene" that I choose.

restart;

with(plots);
with(DEtools);
with(VectorCalculus);
BasisFormat(false);

DEplot({D(w)(t) = x(t) - w(t)*z(t), D(x)(t) = y(t) + z(t), D(y)(t) = -x(t) - y(t) + w(t), D(z)(t) = x(t) + y(t) - z(t)}, [x(t), y(t), z(t), w(t)], t = 0 .. 10, [[x(0) = 0, z(0) = 0.25, y(0) = 0.5, w(0) = 0.165]], scene = [z(t), w(t)], numsteps = 101, axes = BOXED, linestyle = dashdot, method = rkf45, startinit = true, maxfun = 5000, xtickmarks = 10, arrows = medium);

Indeed I want to get something like this:

DEplot([diff(x(t), t) = -0.5*x(t)*y(t), diff(y(t), t) = 0.5*x(t)*y(t) - 0.15*y(t)], [x(t), y(t)], t = 0 .. 40, x = 0 .. 1, y = 0 .. 0.6, [[x(0) = 0.99, y(0) = 0.01]], arrows = medium);

In this plot, we can observe arrows (vector fields), but in the first example, I cannot to handle it.

## Error in intsolve...

Maple

Hi,

I have a problem with intsolve which seems does not cover nonlinear equations:

my code is as follow:

intsolve(fracdiff(u(x, t), t, 1/2) = t^(1/2)*sin(x)/GAMMA(3/2), u(x, t));

But I face with the following error:

Error, (in intsolve) integral equation is not linear.

I searched but I did not find a solution or alternative code to this end.

Do you know the way?

The solution of equation shall be:

u(x,t)=t*sin(x)

## Minimum positive integer solution of sys...

Hi.

I have a question, if it is possible please guide me. I tried for this problem but I failed.

I have a set of linear equations that I want to find the "minimum" "positive" "integer" solution to it. This system may contain free parameters in some cases that they should be set an integer in such a way that they yield our goal namely "Minimum positive solution".

I used isolve but it does not work for this case.

Indeed I especially want that maple use isolve it and then search that if there are "freevars" (in the solution: produced by maple when we use isolve code) or not, if yes then set number such that all solutions be the minimum positive integer set that we can have, indeed, the "freevars" should not set manually, but by the Maple. In the case that there is no "freevar", then maple should give me the minimum positive integer that we can have.

Note that the result must be a unique set of solutions.

For example, one of such systems that I am concerning is as follows which contains freevar in solution when we use isolve.

sys := [a[1] = 2*a[5], a[1] = a[4], 4*a[1]+2*a[3] = a[6]+2*a[7], 2*a[2]+2*a[3] = 2*a[6], a[2] = a[4]+a[5], 2*a[2]-a[1] = 2*a[4]]

## eval diff at parametric point...

Maple

Hi,

I am trying to evaluate the diff of a function at a parametric point. But the outcome seems wrong in comparison with a case that we evaluate diff at a numeric point.

Please observe the attached picture to get my problem.