## ChangeOfVariables doesn't work...

How can I fix the error of ChangeOfVariables: Error, (in Student:-MultivariateCalculus:-ChangeOfVariables) unable to solve the change-of-variables equations for the original variables ?

Thanks!

## Drawing in maple...

I am preparing a document where in I want to show half circle inide the drawing. I can plot a half circle, but can not bring it inside the drawing canvass. Is there a way to show smooth curves inside the drawing. Pencil tool helps to show my curve, but not a smooth one! In any picture tool, bring forward, sent backward options will be there. Are there such tools in maple?

Cheers.

Ramakrishnan V

## Diffusion Equation - inverse solution for finding ...

Hello everyone

I have the solution of diffusion equation from Help of maple website. I put the code here

*****************************

restart: with(plots):

unprotect(D);

alias(c[0]=c0, c[1]=c1, c[2]=c2);
PDE:=diff(C(x,t),t)=D*diff(C(x,t),x,x);
IBC:={C(x,0)=cx0, C(0,t)=ct0, D[1](C)(10,t)=0};
ct0:=1;
cx0:=0;
D:=1;
pds:=pdsolve(PDE,IBC,numeric);
L1:=[0.01, 0.1, 1, 5, 10];
L2:=[red, green, yellow, blue, magenta, black];
for i from 1 to 5 do
pn[i] := pds:-plot(t=L1[i], color=L2[i]):
end do:
display({seq(pn[i], i=1..5)}, title=`Numerical solution at t=0.01, 0.1, 1, 5, 10`);

****************************

the code is working perfectly. But, My question is how can I found the diffusion constant (D) if I have the solution ( C(x,t) ).  Probably it should be an algorithm which use least square method to find (D) based on the data C(x,t).

I am looking for a fast and efficient algorithm if there is any.

thank you so much for your kind attentions in advance

Sincerely yours,

Amir

## why Maple gives all those extra solutions for this...

This ODE turns out to be a simple separable ODE. With one solution, if the ODE is rewritten.

But in its original form, Maple dsolve gives 6 complicated looking solutions with complex numbers in some of them. Even though all 6 solutions are valid.

Any one knows why Maple did that and not give the one simple solution instead?

I used isolate to solve for y' from the original ODE. Verfiied that only one solution exist.  The ODE then became y'(x)= 3*y(x)/(2*x). Which by uniqueness theorem, should have one unique solution in some region in the RHS or in some region in the LHS that does not inculde x=0 ?

Just wondering what is going on, and why Maple did not give same simpler solution, so I can learn something new. That is all.

 > restart;
 > Typesetting:-Settings(typesetprime=true):
 > ode:= 1/2*(2*x^(5/2)-3*y(x)^(5/3))/x^(5/2)/y(x)^(2/3)+1/3*(-2*x^(5/2)+3*y(x)^(5/3))*diff(y(x),x)/x^(3/2)/y(x)^(5/3) = 0;

 > maple_sol:=dsolve(ode);

 > map(x->odetest(x,ode),[maple_sol])

 > solve(ode,diff(y(x),x),AllSolutions)

 > ode2:=isolate(ode,diff(y(x),x)); #solve for y' first

 > ode2:=simplify(ode2)

 > sol:=dsolve(ode2)

 > odetest(sol,ode2)

Maple 2019.1

Physics 395

## Error, (in DEtools/DEplot) vars must be declared a...

Hi, I am trying to plot the phase potrait for this as follow:

s0 := 3*10^5;
d := 10^(-3);
delta := 10^4;
b := 5*10^6;
lamda := 4.16;

DEplot([diff(I(t), t) = s0 + I(t)*(-d - delta*Q(t)/(b + Q(t))), diff(Q(t), t) = -lamda*Q(t)], [I(t), Q(t)], t = 0 .. 10, I = 0 .. 100, 0, Q = 0 .. 100, 0, dirfield = 400, arrows = smalltwo, number = 2, [[0, 4, 0.1], [0, 0.2, 4.1], [0, 7, 0.2], [0, 0.2, 7]], color = red, linecolor = blue, numsteps = 100)

But, there is an error saying "Error, (in DEtools/DEplot) vars must be declared as a list, e.g. [x(t),y(t),...]". However, I did the same for other problem and worked well tho. I have no idea what the problem is for above.

## Mac OS Catalina - 64 bit...

Dear Maple users

I am just curious about how far Maplesoft is updating the Mac version of Maple to 64 bit (Catalina). This version of the Mac OS will hit the shelves in late September this year. As I have been told, no program built on 32 bit will be able to run on this new version of Mac OS. I am pretty sure there will be a lot of software troubles for students upgrading to this version. We can recommend the students not to upgrade immediately, but it would be interesting to hear how far Maplesoft is creating a 64 bit Maple-installer for Mac?

Regards,

Erik V.

## Positive integrand and negative integral value...

int(Integrand, [z = -R .. R, y = 0 .. R], numeric);

plots[implicitplot3d](Phi = phi, z = -R .. R, y = 0 .. R, Phi = 0 .. 0.1e-1, color = ColorTools[Gradient]("Red" .. "Blue", best)[4], grid = [50, 50, 20]);

Why the integrand has positive real amounts in the domain [z = -R .. R, y = 0 .. R] for R=0.5, but the integral value is negative?

## How to Subsitute Animation Parameter into Joint Di...

Hi guys

I've created a joint display which plots a spacecurve and an arrow which represents the tangent to the curve:

I've written this in the animation format so I can move the tangent arrow along the curve, however when I replace

```arrow(subs(s=0,p),subs(s=0,ptan),width=0.3,length=4)
```

with

```arrow(subs(s=A,p),subs(s=A,ptan),width=0.3,length=4)
```

I get the error:

Error, (in Plot:-AnalyzeData:-StandardizeData) points cannot be converted to floating-point values

I have tried animating the arrow alone(see below) and this works fine, so the problem is coming from try to pass the animation parameter A into the display array of multiple plots.

DG.mw

Thanks

## How to solve properly given system of ODE's?...

Hi

I have trouble with solving this ODE system using dsolve command:

and

This system have following solutions:

where

and

C's and A are constants of integration.

They're equations from this paper https://arxiv.org/abs/1710.01910 (45 and 47).

However, my solution differs from correct one - in output there are hypergeometric functions everywhere.

Is there any way to fix/convert this solution? Or to get rid of these functions (my f1 solution looks very close to original one but with coupled hypergeometric function).

sysode := 2*q*(3*q-1)*f1(tau)/tau^2+2*q*(diff(f1(tau), tau))/tau+diff(f1(tau), tau, tau)+(kappa^2+f2(tau))*(1+omega)*(tau/t0)^(-(3*(3+omega))*q) = 0, (54*q^3-30*q^2+4*q)*f1(tau)/tau^3+(24*q^2-4*q)*(diff(f1(tau), tau))/tau^2+11*q*(diff(f1(tau), tau, tau))/tau+diff(f1(tau), tau, tau, tau)-3*omega*(1+omega)*(kappa^2+f2(tau))*q*(tau/t0)^(-(3*(1+omega))*q)/tau = 0;

 (1)

simplify(dsolve([sysode], build));

 (2)

## uses function with the Physics package...

When I apply the uses function with the Physics package in a procedure, the commands in this package are not restricted to the inside of the procedure, but are applied globally. See the example below:

gds := proc(LL, qi, t)

local ta,i;

uses Physics;

ta := sec(diff(diff(LL, diff(qi[i](t), t)), t), i = 1 .. nops(qi));

RETURN(ta) end:

sxy := diff(x(t), t)^2 + diff(y(t), t)^2:

gds(sxy, [x, y], t);

Error, (in Physics:-diff) name expected for external function

On the other hand, when I apply the uses function with the LinearAlgebra package in a procedure, the commands in this package are restricted to the inside of the procedure only.
dst:=proc(MM)

local DA;

uses LinearAlgebra;

DA:=Determinant(MM);

RETURN(DA) end:

dst(<<1 | 2>, <3 | 4>>);

-2

Determinant(<<1 | 2>, <3 | 4>>);

Determinant(Matrix(2, 2, [[1, 2], [3, 4]]))

This could be a bug in Maple 2019?

## How to create subgraph for a directed graph...

Hello, I am wondering if Maple is capable of generating a subgraph for a directed, weighed graph with the GraphTheory package. The online resources I can find only include undirected, unweighed graphs.

can you please include an example with commands that is able to perform the said task?

## solve the equation ...

hi everyone:

how can I solve this below equation?

w:=(x)->sin(lambda*x)+b*cos(lambda*x)-sinh(lambda*x)-b*cosh(lambda*x);

b := -(sin(lambda*L)+sinh*lambda*L)/(cos(lambda*L)+cosh*lambda*L);

L:=10;

equation:=int(w(x)^2,x=0..L)=1;

lambda=????

tnx..

## solve PDE with Runge-Kutta method...

Hi everybody?

how can I solve this PDE with Runge-Kutta method and 2D plot in terms of w(x,t) , t and 3D plot in terms of t, x, w(x,t)?

code1.mw

## a question on integration of error function functi...

how this integral can be calculated in the simplest form ? the second question is what exactly is done when using assuming? for example when using assuming real, all the functions or parameteres are affected? thanks in advanced

 > restart:with(IntegrationTools):
 > (int(int(exp(-(y-beta[0]-beta[1]*x-b0-b1*x)^2/(2*sigma^2))*exp(-b0)*exp(-b1),b0=0..infinity),b1=0..infinity,continuous=true) assuming real)
 (1)
 >