0
$\begingroup$

Suppose I want to sum a function, $f(\{m_a\})$, of several variables, $m_a$, $a=1,..,n$, which run over ranges, $1,...,k[[a]]$, however, I do not know $n$ in advance. I thought I could do this using ``Apply,'' namely:

Apply[Sum,Join[{f[Table[Subscript[m,a],{a,1,n}]]},Table[{Subscript[m,a],1,k[[a]]},{a,1,n}]]]

However, I'm running into the following problem. The function $f$ is getting called only once, at the argument ``$\{m_a\}$'', ie, before assigning them the numerical values being summed over. If the function requires numerical inputs, this won't run properly. However, if I write the corresponding Sum by hand (ie, in cases where I know in advance what $n$ is), then $f$ is called for each term in the sum, and there is no problem. How can I make this sum behave as I'd like for arbitrary $n$?

$\endgroup$
0
$\begingroup$

I was able to find a solution, which is instead to use:

Sum[f[Table[Subscript[m,a],{a,1,n}]],Evaluate[Sequence@@Table[{Subscript[m,a],1,k[[a]]},{a,1,n}]]]

Although I'm still curious why the previous method doesn't work.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.