## How can I group certain variables and integers of ...

Asked by:

I'm still quite new to maple and I'm working calculating some dynamic equations.

I want to be able to selectively group certain variables or numbers depending on how I need the equations to be showed, I don't know if that's possible, I´ll explain further.

In typewritting extended format one equation is shown like this:

And maple standard:

The fisrt thing I want is to show the time derivatives in the dot representation, but I also want the 1/2 multiplyting each term of the whole equation like in the maoke standard format.

I also need to group certain variables in some other equations I have and I was wondering if there is a way to do this.

## Why do I obtain a wrong answer using diff()?...

Asked by:

Since I am a very recent Maple user, I do not know why I obtained a wrong answer with the following two comands:

Exp:= Psi(rho(x,t),theta(x,t));
Psi(rho(x, t), theta(x, t))
Exp1:= diff(Exp,t);
/ d           \
|--- rho(x, t)| D[1](Psi)(rho(x, t), theta(x, t))
\ dt          /

/ d             \
+ |--- theta(x, t)| Psi(rho(x, t) + 1, theta(x, t))
\ dt            /

Can someone, please, help me?

Thank you.

## Partial derivative of multivariable function using...

Asked by:

Problem.mw

Hi,

I want to know the partial derivative of

where

in order to

ρ

If I write

I obtain this

which is incorrect  since I did not have any indexes in sigma. However if I do this next command the result seems correct although no substituion of rhocrf

What I would like to obtain was the solution in order to rho and not to rhocrf and additionally having the result as a summation over p and q and not the extended result. How should I write it in Maple then?

Thank you very much!

## How to collapse derivatives?...

Asked by:

Let

z := Diff(x(t),t)*y(t) + x(t)*Diff(y(t),t);

Is there a way to tell Maple to collapse that into Diff(x(t)*y(t), t) ?

I tried factor, combine, simplify, but none of them worked.

## Error, (in eval/diff) invalid input: diff received...

Asked by:

hi .in substuting in ode equation i encounter with error

Error, (in eval/diff) invalid input: diff received (f1[i+1, i]-2*f1[i, i]+f1[i-1, i])/h^2, which is not valid for its 2nd argument

please help me

thanksh_2.5_eq4.mw

 (1)

 (2)

 (3)

Download h_2.5_eq4.mw

## How to convert a huge expression from Maple to Mat...

Asked by:

Dear all:

I have used the "diff" command in Maple to help me derive a huge and very long function, and now I want to convert this huge expression from Maple to Matlab format, for example, into a Matlab .m file. The format of this expression in Maple is very different from Matlab.

So could you help me with this problem?

Thank you all.

## an error occurred, diff received 0...

Asked by:

Hello, I have a function defined as

g :=  (x, y)->diff(u1(x, y), x, x)+diff(u2(x, y), x, y).

I want to define another function as follows

f :=  (y) ->subs(x = 0, g(x, y)) ,

Now, when I want to calculate numerical values for the new function f(0), f(0.1), f(0.2),..... and so on. The following massage appear

Error, (in f) invalid input: diff received 0, which is not valid for its 2nd argument.

What is the problem here.

Amr

## How to differentiate to a variable in function of ...

Asked by:

EDIT: My question has been  answered below

Hello,

Lets' say I have the equation L:

L=

I want to take the partial derivative of L to diff(theta2(t), t).

Maple doesn't allow me to do this: diff(L, diff(theta2(t),t));

How can I solve this problem?

I hope someone can help me. Thanks in advance!

Loïc

## Error with Physics[diff]...

Asked by:

Hi everybody;

I have a problem with Physics[diff] command. When I run the following code, error messages appear where the Physics[diff] command exist. What is the source of error? How can I fix it?

Thanks in advance

Q1.mw

## creating functions with derivatives in them. How d...

Asked by:

I wish to define a function which is the derivative of another function.

> f:=(x)->x^2:

> g:=(x)->diff(f(x),x):

> g(x);

2 x

> f(2);

4

> g(2);
Error, (in g) invalid input: diff received 2, which is not valid for its 2nd argument

I cannot find a way in which I can define the function g, using the functional operator, so that I can actually evaluate g(x).

How can I do this?

## Notation of diff and ' that is diff(f(x),x) and f'...

Asked by:

#Hello people in Mapleprimes,

#After

restart;interface(typesetting=extended);

diff(f(x),x);

#shows f'(x).

#But,

diff(f(t1),t1);

#shows just df(t1)/dt1, not f'(t).

#Can't I show f'(t1) not df(t1)/dt1?

#Is this a way peculiar to Maple?

#I hope someone could give me some hints.

#Best wishes.

#taro

## How can I apply this differential in Maple?...

Asked by:

hi

how i can apply this differential in maple?

thabks...

## Problem with KelvinBei function...

Asked by:

Hello,

I need to crate a function to be evaluated in a range of values, and this function i would to use in other expression, example:

cel1      "seq(i,i=0.001..2,0.001)"

cel2      "A:=&1";cel1

cel3      "f:=x->diff(KelvinBei(0,x),x)"

cel4      ""B:=map(x->f(x),[A])"

This is ok with a lot of function but with diff(KelvinBei(0,x),x) in cel4 show this error "Error,(in f) invalid input:.1e-2, which is not valid for its 2nd argument.

Why??? How can I do??

## Eval Physics[diff]...

Asked by:

Hey all,

I want to symbolically differentiate a function and recalculate the result later. Here is what I have tried so far:

 > restart;
 > myexp:=dfdb+sthlong
 (1)
 > b:=;
 (2)
 > dfdb:=Physics[diff]~(f(b),b)
 (3)
 > f:=b->b(1)^2+b(2)
 (4)
 > eval(myexp);  #actual result
 >
 >
 (5)
 > dfdb:=Physics[diff]~(f(b),b):
 > eval(myexp); #expected result
 (6)
 >

Download physics_diff.mw

I wonder if this is even possible, or if I missunderstand something. Can you please help me?

Thanks

Honigmelone

## Modeling of DC Motor. Problem with DiffEquation...

Asked by:

Hello,

I'm modeling the simple DC motor system in Maple.
The equations describing the system;

eq1:=J*diff(theta(t),t,t)+b*diff(theta(t),t)=K*i(t):
eq2:=L*diff(i(t),t)+R*i(t)=V(t)-K*diff(theta(t),t):
DCMotor:=[eq1,eq2];

First, I create the system using DiffEquation:

Sys:=DiffEquation(DCMotor,[V(t)],[theta(t)]);

And now I have problem. The input var is V(t) (input voltage) and the output var is theta(t) (position of the rotor).

But I wont to have in output var not position of the rotor but speed of the fotor - diff(theta(t),t)

How to set output var for diff(theta(t),t) (the speed of the motor)?

Best

Rariusz

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