## Is there a way to have diff(f,...) with f a symbol...

Hello,

I'm trying to write and simplify expressions involving partial derivatives of an arbitrary function, say f(x,y).

Specifically, I would like  to evaluate to , instead of

And  gives the same result.

Interestingly,  does evaluate to , as expected.

I could get some results by using a custom differentiation function

diff/f := proc(x,y,v)
if v = x then return D[1](f)(v,y):
elif v = y then return D[2](f)(x,v):
else return 0: # is there a fallback I can use without risking infinite recursion?
fi:
end proc:

and it works for the simple case, but now  does not work.

All this makes me feel that there must be a way to get what I want by default, but I can't figure it out.

Is there? Thank you in advance!

## how to edit display of partial derivatives...

is there a possibility to display the partial derivative of f(x,y) wrt. y as

and second order / cross-partials accordingly?

thx

jo

## Why do braces limit evaluation?...

Is there a help page which explains why braces provide the partial text evaluation in this code?

RopeLen := 30;RopeAddLen := .5;

plots[textplot]([1, 1, typeset("%1", (({(1/2)*RopeLen}+{(1/2)*RopeAddLen})^2-{(1/2)*RopeLen}^2)^(1/2))])

## How to solve a PDE?...

Hi,

i meet  a partial differential equation seems not complicated

with(PDEtools):

PDE := (diff(f(x__1, x__2, p__1, p__2), x__1))*p__1/m-(diff(f(x__1, x__2, p__1, p__2), p__1))*(2*k*x__1-k*x__2)+(diff(f(x__1, x__2, p__1, p__2), x__2))*p__2/m-(diff(f(x__1, x__2, p__1, p__2), p__2))*(-k*x__1+2*k*x__2);

when i use

pdsolve(PDE);

i get nothing,but i sure

f=c*(p__1^2/m+p__2^2/m+4*p__1*p__2/m+6*k*x__1*x__2)

is the one solution of the differential equation .

how i can get solutions about of the above equation.

thanks .

## IBS incorrect. How to write?...

There is a desire to explore the process of filtration combustion. To do this, you must solve a system of differential equations in partial derivatives.
I write down all the equations.
Boundary conditions in Maple 2015.0 interpreted incorrectly.
I need to write like that:

given that:

It turns out so:

ie somewhere lost derivatives

,....

As in Maple record boundary conditions correct?

Thanking you in advance.

## Partial derivative syntax ...

I am entering into Maple, but it interprets it as

How do I change this partial derivative to a total one. (Both x and y can be assumed invertible functions of parameter u and their derivatives are nonzero)

## Derivative from pdsolve/numeric solution?...

Is it possible to somehow extract a derivative from numeric solution of partial differential equation?

I know there is a command that does it for dsolve but i couldn't find the same thing for pdsolve.

The actual problem i have is that i have to take a numeric solution, calculate a derivative from it and later use it somewhere else, but the solution that i have is just a set of numbers an array of some sort and i can't really do that because obviously i will get a zero each time.

Perhaps there is a way to interpolate this numeric solution somehow?

I found that someone asked a similar question earlier but i couldn't find an answer for it.

## How to Plot Partial Sum Sequence...

I'm trying to find the partial sum of the function. Now I need to plot the first couple partial sums onto 1 graph.

I'm not really sure how to input the plot function. I was able to graph it by inputting each partial sum function but I would prefer an easier solution.

## Partial Fraction expansion of a bivariate GF...

Hi, I have a bivariate generating function that looks like this

where x is enumerating by binary strings by length and k is counting a number patterns in the string. I would like to convert the series into partial fractions. Convert[parfrac] only seems to work when k is given a value, which I did for several small small choices, from which I guessed the general partial fraction decomposition. Would someone have an idea on how to extract the partial fractions directly in terms of x and k?

Thanks,

best, Luke

## How do I solve this system of PDEs in Maple?...

Hi there,

I'm quite new to Maple so please forgive me! I have a system of partial differential equations I'm trying to solve in Maple as such below

df/dt = f(1-f) - f * h

dg/dt = g(1-g) * Gradient(1-f * gradient(g))

dh/dt = (g - h) + Laplacian(h),

where f,g,h are functions of space and time (i.e. f(x,y,z,t)). I guess my first question is - is this possible in Maple to evaluate? (I'm currently unsure on ICs as I'm figuring it out from the model - it's a model for cancer growth I'm trying to evaluate but have a rough idea of what I'd use).

If it is possible, can you please share how I'd write this? Everytime I've tried I seem to be failing to define anything properly, so your expertise would be greatly appreciated!

## over detemined system...

i have got alot of mixed and high degree derivatives. For example:

u[x]*u[x,t]*eta[x,t]+u[]^2*u[x]*eta[x]+kis(x,y)u[x,t]^2*u[]+eta(x, y)*u[]*u[x]^2+ksi[x,t]*u[x]^2*u[x,t]+......

like this alot of terms

my question is how can i solve divided by the derivative of the u(x,t) partial differential equations system and so  how can i find eta(x,t,u) and ksi(x,t,u)

## PDE, Chain Rule ...

Hey everybody I am trying to get maple to do some partial differention for me.

Where

I have PDEtools on but, it doesnt return an expression correctly. It's I think the problem is because Ψ is a function of (x,y) and f is a function of η and η is a function of x and y . U and ν are constants. vand vy are the x and y velocites.

What I would like the program to return when I write

is something along the lines of

could someone give me a hand on this. I would really apperciate it.

Best Regards,

Kyle

## Solving a differential equation (involving phase s...

Hi, I am looking for some help for a computation on Maple. I have the following objects

## Problem with initial/boundary conditions solving t...

Hello,

I'm trying to solve the effects (deflictions, tensions, etc) of a load on a timoshenko beam. It uses two partial diffential equations, wherein q is the load:

> PDE1 := kappa*G*A*(diff(y(x, t), x, x)-(diff(theta(x, t), x)))-rho*A*(diff(y(x, t), t, t))-q;> PDE2 := E*J*(diff(theta(x, t), x, x))+kappa*G*A*(diff(y(x, t), x)-theta(x, t))-rho*J*(diff(theta(y, x), t, t));

The boundary conditions are that in the corners the moments (derative of theta...