When doing variable change for a differential equation, dchange works well for transformations like {s=r sin(theta),z=r cos(theta)}, but it does not seem to work if you include constant values like {s=(k-1)*r sin(theta)}, how can I let maple know that k is to be treated as a constant?

Could someone help me fix this loop.

It is printing the expressions without evaluating but it is evaluating it before appending it to the list.
I do not want to apriori define the functional dependence i.e. f(t).

lis := [f1, f2, f3, f4, f5, f6, f7, f8, f9, f10];
L := [];
for i in lis do
    print(subs(f = i, 'diff(f, t)'));
    L := [op(L), subs(f = i, 'diff(f, t)')];
end do;
print(L);

I want to write an if statement with a matrix R:
such that maple executes command 1 if R is Matrix(4, 4, [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]])

and command 2 if R is not zero.

What is the easiest way to go about this?

I was wondering if there was a command that could tell me if an expression consisting of undermined functions was always positive (with real domain).

For example f1:=f(x)^2+g(y)^4 is always positive.

but f(x)^2-g(y)^2 is only positive on a restricted domain.

I have a lists within lists.  I needed to search for a specific element in the sub-list and need to extract each such sublist that has an element.

I am only familiar with the search tool. Could someone suggest a simple way to do this.

For example, I have the following.

s := [{f0(t, r) = 0, n(t) = n(t)}, {f0(t, r) = 0, n(t) = 0}, {f0(t, r) = 0, n(t) = 0}]

I need to extract the sublist that has n(t)=n(t) so only the first element of the list s.