Hi, I am looking for a way to extract a specific operand from a given expression. Something similar to the coeff command, but rather than just the coefficient, I want the whole term. For example,
Given an expression A:=u[1,2]+u[2]*u[1,1,1], if I want to extract the term u[2]*u[1,1,1]. then a command, let's say LT which takes the expression and a component, which then will return the term containing that component.
input: LT(A, u[1,1,1])
output: u[2]*u[1,1,1]

Thank you for your help.

For an expression like , I want to extract the subscripts in an another set/list [{1,1}, {2,3}, {1,1,2}]. Any help is much appreciated. Thanks

I am working with the JetCalculus package along with the DifferentialGeometry package. Notation: if there are 2 independent variables (x,y), then u[1,2] would now represent the 3rd mixed partial derivative of u, once with respect to x and twice with respect to y. Please check Example 3 here, https://de.maplesoft.com/support/help/Maple/view.aspx?path=DifferentialGeometry/JetCalculus/TotalDiff

If I have an expression like u[1,0]+f(u[0,0])*u[0,1]+u[1,1]*u[0,3], then I am looking for a procedure which gives me the Lead derivative term. In the example above, it is u[1,1]*u[0,3], and then I can find the lead coefficient, i.e u[1,1].
Please note that the Lead derivative is not unique and can have several terms. For example, orders are the same for u[1,1] and u[0,2].

Idea: If I can find a way to extract the subscripts and do operations on them, then it would be very helpful. 
Any help/guidance is much appreciated. Thanks.
EDIT 1: LeadingDerivative command is not the solution for me.

Hi everyone

I am stuck in my code. I have a multivariate polynomial and I am trying to define an order on the variables such that I can write my polynomials in a desired normal form. I tried with the Groebner package but that's quite different from what I want.

I want to define the order on the variables as u[i]=v[i] and u[i]<u[i+1].

Lets say my polynomial is f then,

input f= u[1]^2+u[2]+v[3]

output f = v[3]+u[2]+u[1]^2.

If there is a clash between u and v then, either of them can come first, for example,

input f= u[1]^2+u[2]+v[3]+u[3]^2

 output f=v[3]+u[3]^2+u[2]+u[1]^2 or f=u[3]^2+v[3]+u[2]+u[1]^2

I hope my question is clear. Thank you for helping me out. Your time is much appreciated :)
EDIT 1: Comment towards the end of the answer is a solution for this question.

with(DifferentialGeometry):with(JetCalculus):
DGsetup([x],[u],E,5);
vars≔x,u,u[1],u[1,1],u[1,1,1];
PDEtools[declare](Q(vars));
TotalDiff(Q(vars),x);
TotalDiff(u[1,1],x);

Hi everyone,

Recently I came across the total differentiation command in the PDEtools. For its

documentation, I used the following link

http://www.maplesoft.com/support/help/Maple/view.aspx?path=DifferentialGeometry/JetCalculus/TotalDiff

Unfortunately, when I try to replicate this it did not work as expected. I am getting the total derivative of the expression to be zero. I do not understand where I am going wrong.

You can find my code above. I am also attaching the screen shot of my maple file.

I would really appreciate if someone could help me out. Thanks for your help.