Apologies in advance if the title is vague, I'm not really sure what to call this.
I have a function (call it 'foo') that generates a largeish polynomial, and it is natural to make the variables be
x[1],x[2],x[3]
and so on, so I get a polynomial, e.g.
x[1]^2 x[2]+x[3]
Now, I'd like to store this as a function
bar[x[1]_,x[2]_,x[3]_]:=foo[whatever]
This doesn't work, of course, but if the variables were e.g.
x1,x2,x3
etc. instead, I could do
bar[x1_,x2_,x3_]:=foo[whatever]
and that would work. I figured some replacement rule would work, e.g.
rule={x_[i_] :> ToExpression@(ToString[x] <> ToString[i])}
which looks like it should work:
x[1]^2 x[2]+x[3]/.rule
gives output
x1^2 x2 + x3
but if I define
bar[x1_,x2_,x3_]:=foo[whatever]/.rule
then
bar[1,2,3]
outputs
x1^2 x2 + x3
instead of 5, which it should.
Obviously, there is something I don't really understand about the way Mathematica handles variable names, and what I'm trying to do to fix this is probably too naive. Is there some better way to get around this problem?
Thanks in advance for any help.
