On 05/28/2018 08:53 AM, Marduk wrote:
> Dear all,
>
> As the following example shows, when writing polynomials with noncommutative
> variables one has to specify that the symbols belong to the list of NC
> variables:
>
> ops := OVAR[A,B]
>
> ncomm := XDPOLY(ops, Integer)
>
> q : ncomm := 3*B::ops*A::ops
>
>
> I just found out that doing the same in REDUCE is more pleasant, since one
> can
> tell the interpreter that some identifiers are to be treated as
> noncommuting variables:
>
> nc_setup({A,B});
>
> A*B - B*A;
>
>
> How could one achieve the same with FriCAS?
Just don't compute with symbols. Turn the symbols A and B into elements
of the respective domain, i.e. make them noncommutative polynomials.
ls: List Symbol := ["a"::Symbol, "b"::Symbol]
ops := OrderedVariableList ls
NPol := XDistributedPolynomial(ops, Fraction Integer)
vars :=[index(i)$ops::NPol for i in 1..#ls]
a := vars.1
b := vars.2
a*b - b*a
Note that instead of
"a"::Symbol
you can also simply write
'a
That notation seems to be influenced by LISP and denotes the VALUE
of a symbol with name a.
As long as the programming variable a is unassigned in the current
session, you can also simply write a and the interpreter will try to
figure out would you could have meant by it. With
"a"::Symbol
however, there is no doubt.
Enjoy.
Ralf
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