## Error, (in pdsolve/BC) invalid subscript selector ...

Hello,

I am trying to solve some coupled equations. however, I keep getting the error ' invalid subscript selector.

Does anybody have any solution for this?

here is the file : -

error.mw

Thanks !

Regards,

Mota

## 3D Graph of Parabloid...

I am so sorry for all of the questions. I am getting extremely frustrated with Maple.

I want to plot a 3D rendering of 4x^2+9y^2 but I want the full paraboloid to show. However, all I keep getting is cut off versions.

## coords constants used in transform ...

In some coordinate systems availiable in the plot command, there are constants specified symbollically, for example,for logarithmic, the constant "a" is specified (see ?coords help page) is there a simple way to retreve the numerical value for these transformation parameters, or does it need to be obtained by appropriate manipulation of the data set?

## how can i obtain the corresponding polynomial for ...

how can I obtain the corresponding polynomial for a  propositional formula ?

## Working with the Student[VectorCalculus package...

I must say that using the help for this package is not intuiative. ( in general for all )
Once on a page for command i can't  go back to the home page where the mainpage is for the package
Example i was doing something with gradient command and try figure out how to make a function out of it

So i want to look at the eval command in the student vectorcalculus package
This could be easy if there was a button to see all commands ( a home button) on the gradient page

Now i must type in help again ..
evalVF gives a column vector notation , but mixing both notations ? ( as vector , as column vector)

```gf := Gradient(exp(x*y^3*z^2))
```

This i can evaluate via contectpanel for  f(x,y,z)  in a point and as output a colomn vector

Making a vectorfunction for gf is not possible via contectpanel ? , or do i miss something

Note: perhaps showing the package commands in the working document is a idea

## how to plot dualaxisplot in dialog?...

try:
p := dualaxisplot(listplot(ma, color = red), listplot(me, color = blue), style = line, gridlines = false);
catch:
p := dualaxisplot(listplot(me, color = red), listplot(me, color = blue), style = line, gridlines = false);
end try:
return p:
end proc:

CheckGraph := proc(text,graphparam1,graphparam2)
local maplet, choice:
maplet := Maplet(
[
[Plotter['PL1'](graphparam1)],
[Plotter['PL2'](graphparam2)],
#[Plotter['PL2'](graphparam2)],
[text, ComboBox['CoB1']("No Refund", sort(["Jackpot"], lexorder))],
[Button("OK", Shutdown(['CoB1'])), Button("Cancel", Shutdown())]
],
):
choice := Maplets[Display](maplet):
end proc:

>graph1
can show graph but after using Plotter['PL1'] , it can not show graph in dialog

CheckGraph("Has Jackpot?",graph1,graph2):

how to plot dualaxisplot in dialog?

## factoring with exponentials...

I would like to factor an algebraic expression that contains exponentials.
Maple spits it back unfactored. Did I enter it wrong?

factor(exp(4*y) + 2*exp(2*y) + 1);

## Problem with DEplot3d...

Good afternoon everybody,

I am a beginer user in maple and I am having problems to plot a system of differential equations. My code is

----------------------

restart; with(VectorCalculus); with(LinearAlgebra); with(DEtools);
> p := 2*u*x*y^2; q := (x-1)/x;
> doth := simplify(-(sqrt(6)*x^3*(y-1)^2+u*((3+sqrt(6))*x^3*(y-1)^2+3*y^2-9*x*y^2+3*x^2*(y^2+2*y-1)))/p); ddotphi := simplify((y-1)*(sqrt(6)*x*y^2*(x-1)+u*(3*y^2-(6+sqrt(6))*x*y^2+x^2*((3+sqrt(6))*y^2+6*y-3)))/p);

>ode1 := diff(x(t), t) = x(t)*(1-x(t))*doth-x(t)^2*ddotphi/sqrt(6); ode2 := diff(y(t), t) = y(t)*(y(t)-1)*doth; ode3 := diff(u(t), t) = sqrt(3/2)*u(t)*(1+u(t))*q;

>DEplot3d([ode1, ode2, ode3], [x(t), y(t), u(t)], t = -2 .. 2, x = 0 .. 1, y = 0 .. 1, u = -1 .. 0, [[x(0) = .9, y(0) = .25, u(0) = -.95], [x(0) = .9, y(0) = .25, u(0) = -.5], [x(0) = .85, y(0) = .2, u(0) = -.15], [x(0) = .25, y(0) = .5, u(0) = -.5], [x(0) = .7, y(0) = .5, u(0) = -.6]], linecolor = [red, green, black, navy, maroon], thickness = 2, axes = boxed, labels = [x(t), y(t), u(t)], arrows = medium, stepsize = 0.1e-1, orientation = [30, 65]);

--------------------------

and the next error appears

Error, (in DEtools/DEplot/direction3d) unable to store 'HFloat(HFloat(undefined))+HFloat(HFloat(undefined))*I' when datatype=float[8]

I have no idea what to do, and searching for solutions I have only found things that I dont understand.

Thank you very much in advance

## Why is this happening?...

I want the legend to be produced to look like the third to last example. https://fr.maplesoft.com/support/help/Maple/view.aspx?path=plots/contourplot

However, mine keeps coming out like this.

## solving multivariate functions who migth be a part...

hello how do i solve these equations and what type exactly are they ? so i can find more information

(i dont understand if this is a partial-something)

for the following function

i need to evaluate it at the following point

fy(pi/2,pi)  and  fz(pi/2,pi)

this is the part i dont understand how to do, i keep getting 0 in the equation.

thanks for you! and your time

## Is it possible to execute a section without select...

I would like to "run" or execute parts of my code that I put in a same section. Unfortunately, selecting "Execute" when right-clicking on a section does nothing...

Maple

## using indexed name for variable vs. two underscor...

For entering system of linear ode's, from textbook, such as this example

I can either use x[1],x[2]  or x__1 and x__2.

Maple dsolve works with both. The Latex generated is also exactly the same Which is x_{1} and x_{2}.

The only minor difference I see is on the screen in the worksheet (I only use 1D), where the subscript looks a little nicer in the case of x[1] vs. x__1

The subscript in the case of x[1] is upright while the one in x__1 is italic. I like the first one more.

Other than this cosmetic difference, Are there are subtle sematic differences between the two forms in terms of computation? I know x[1] create table x. OK.  While x__1 is a separate symbol. No table is created.,

Which would be  a safer/better option to use in this case?   Or is it just a matter of choice?

```sys:=[ diff(x[1](t),t)=x[1](t)+x[2](t),diff(x[2](t),t)=x[1](t)+3*x[2](t)];
sys:=[ diff(x__1(t),t)=x__1(t)+x__2(t),diff(x__2(t),t)=x__1(t)+3*x__2(t)];
```

In some way, using x__1(t) might be a little easier to read on the eye than x[1](t) since there is only one type of paranthesis involved.

ps. I tried to search for __ in Maple help to read more about it, but ?__ do not show it. I am sure __ is in the help under some other name.

## Empty or null values in matrices...

How do I insert an empty or null value into a matrix imported from a csv file?  The imported data assumes the value is zero.

## replacing pattern in expression...

For display only purposes, to get the Latex looking better, I replace the constant of integrations Maple using which is _C1, _C2., etc... to c[1],c[2],.....

This is something I do at the very end of computation, just before I get the Latex of the expression.

The way I do this now, is not good. .And I am asking if there is a better way to do this replacement. In Mathematica, I can do this using a patterm where I tell it to replace  C?  by c[?] where ? means anything.

Is it possible to do something like this in Maple? Here is an example

```sol:=dsolve(diff(x(t),t\$3) = x(t));
```

This gives solution as

And just before ask for the Latex of this, I change it to

This is done using a function. Please see worksheet below.

The problem with the current solution is that I do not know how many _C there are, so I assumed 10 as worst case, which works for my case. But I prefer a more general solution, may be using pattern in the subs command?

 > restart;
 > replace_all_C:=proc(expr::anything) local n,N,c; local new_expr; local max_count :=10; #worst case, since do not know how many     new_expr:=expr;     for n from 1 to max_count do         N:=convert(n,string);         new_expr:=subs( :-parse(cat("_C",N))=:-parse(cat("c[",N,"]")),new_expr);     od:     return new_expr; end proc:
 > sol:=dsolve(diff(x(t),t\$3) = x(t)); tmp:=replace_all_C(sol)

 >