about concatenation "a||b" in Maple?

Question

I test the code

    L:=[2,1];
    sum('a||b*L[1]', 'b' = 1 .. 2);

It returns a1*L[1]+a2*L[1], but I expect to get a1*2+a2*2 after evaluation of L[1]. Any ideas?

Thanks.

EDIT:

I have one further question. Here's the test code:

    L := [2, 1]
    test := proc (i) local a1; a1 := 1; add(a || b*L[i], b = 1 .. 2) end proc
    test(1);

will result 2 a1 + 2 a2 without evaluating a1 which is a local variable defined in function test. I expect to get 2*1+2*a2. Any further idea?

Answer 1

Your first line is just an equation, with =, and not an actual assignment with :=. So you weren't doing an assignment to L.

And the uneval quotes are misapplied, in the sum call, and wrap too much.

You could also use add instead of sum, to rely on the special evaluation rules of add and thus get rid of the need for the uneval quotes.

> L:=[2,1];                          
                              L := [2, 1]

> add(cat(a,b)*L[1], b = 1 .. 2);
                              2 a1 + 2 a2

> add((a||b)*L[1], b = 1 .. 2);  
                              2 a1 + 2 a2

> sum('a||b'*L[1], 'b' = 1 .. 2);    
                              2 a1 + 2 a2

> sum('cat(a,b)'*L[1], 'b' = 1 .. 2);
                              2 a1 + 2 a2