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Can a function be made to accept a variable amount of inputs?

4 answers

In the following code what would be the simplest way to generalize it to say some NfNfN_f number of zzz instead of just z1z_1 and z2z_2?

$Assumptions = {1 > y > 0, 1 > z1 > 0, 1 > z2 > 0};

Nmax = 40;

LnMT1 = -Sum[Log[1 – (1/(1 + x^n)) (x^(n/2) (y^(n/2) + z1^n + z2^n) +

x^(n/2) (y^(-n/2) + z1^(-n) + z2^(-n)))], {n, 1, Nmax}];

LnMT2 = Sum[(1/n) (Sum[x^(k*(n/2))*Subscript[f, k][y, z1, z2, n],

{k, 1, Nmax}]/(1 – x^(2*n))), {n, 1, Nmax}];

For[i = 1, i <= Nmax, i++, temp[y_, z1_, z2_] = Simplify[Solve[SeriesCoefficient[LnMT1 - LnMT2, {x, 0, i/2}] == 0, Subscript[f, i][y, z1, z2, 1]][[1, 1, 2]]]; Print["coefficient of ", x^{i/2}, " = ", Expand[Simplify[temp[y, z1, z2]]]]; Subscript[f, i][y_, z1_, z2_, n_] = temp[y^n, z1^n, z2^n] ] I guess the places where there is a sum over the nth powers of z1 and z2, they canbe replaced by Sum[z[j]^n, {j, 1, Nf}] but the problem is with the "functions" "temp" and fif_i which will need to handle NfN_f number of variables. I tried defining expressions like, g[Table[z[i], {i, 1, Nf}]] = Sum[z[j]^2, {j, 1, Nf}] but I couldn't do anything with them. And I anyway don't know how to define a function of NfN_f variables. (..one can't pass values to the above gg...and in the above code one would want to even functionally update fif_i as in the last line of the loop. Also in the "Print" line when I am printing out the evaluated expression for temp often I want to print the value of temp with one or more of its variables (y and z) being set to 1. If the above code can be generalized to arbitrary number of z then how would this setting to one be done then? Note: in all of it I am assuming that at the start there will be a new line declaring the value of NfN_f to be used as is being done now for Nmax ================= ================= 3 Answers 3 ================= When you define a function, you use Blank to match exactly one expression. Therefore z1_ stands for match one parameter. As you might have seen, we have BlankSequence (__) and BlankNullSequence (___) too. The former matches one or more expressions, while the latter matches zero, one or more expressions. Therefore, you can define a function like f[z__] := {z} f[a] f[1,{123},b,c] f[a,b,c] (* {a} {1,{123},b,c} {a,b,c} *) to match as many parameters as you like. You can of course do something with the parameters g[z__] := Sum[Sqrt[elm], {elm, {z}}] g[a,b,c,d] (* Sqrt[a]+Sqrt[b]+Sqrt[c]+Sqrt[d] *) You may now say *but I cannot access single z1 for instance. First, yes you can h[y__] := With[{z = {y}}, z[[1]] + z[[5]]] h[a, b, c, d, e] (* a + e *) but secondly, what would be the use of this? When I access z[[5]], the function is not general anymore, because I expect always at least 5 parameters. Didn't understand how your answer corresponds to my question. Now I can define 2 variable functions like f[z1,z2]:=f[z1_,z2_] := and I can manually keep increasing it by adding extra zs through the code by hand. What I want to do is to define ff such that it is a function of NfNf zs and be able to set the value of Nf at the beginning. – user6818 Dec 13 '12 at 3:12 @user6818 Can you come to chat? – halirutan Dec 13 '12 at 3:37 yes I am logged into chat – user6818 Dec 13 '12 at 3:59 Perhaps you can use Repeated? A function with five arguments: ClearAll[h]; h[z : Repeated[_, {5}]] := Plus @@ {z} {h[1], h[1, 2, 3, 4, 5], h[a, b, c, d, e], h[1, 2, 3, 4, 5, 6, a]} (* {h[1],15,a+b+c+d+e,h[1,2,3,4,5,6,a]} *) another example with five arguments: ClearAll[h2]; h2[z : Repeated[_, {5}]] := {z}[[2]] + {z}[[3]] {h2[1], h2[1, 2, 3, 4, 5], h2[a, b, c, d, e], h2[1, 2, 3, 4, 5, 6, a]} (* {h2[1],5,b+c,h2[1,2,3,4,5,6,a]} *) Another alternative is to use Condition ClearAll[h3, h4, h5]; mm = 5; h3[z___ /; Length[{z}] == mm] := Max[z] h4[z___] /; Length[{z}] == mm := Max[z] h5[z___] := Max[z] /; Length[{z}] == mm Looking just at the question in the title without going through the rest of the code, my simple answer would be to define your functions to take exactly one argument zList at all times, where zList is a List (as the name says). This list can have any number of arguments, and the function can run through them in a way that adapts to Length[ zList ] (preferably by using constructs like Map that operate on the whole list at once). The issue is with being able to treat each of these zs as variables to which values can be passed. You can see how "temp" needs to be defined in the first line of the loop and how fif_i is updated by temp in the last line of the loop. How would one achieve these even if I make these functions of tables of z? Also in the "Print" line I often want to print the value of temp with all of its arguments set to a value 1. How does one achieve that? – user6818 Dec 13 '12 at 8:53