# Define a function interactively with sum

I have to define a function which has 1e4 terms added up together.

f(x1, x2) = (sum i, j, k, l from 1 to 10) (C(i) * C(j) * C(k) * C(l) * exp( (alpha(i)+alpha(j)) * x1 + (alpha(k)+alpha(l)) * x2 )

all C and alpha are known and f is a function of x1 and x2.

Is there any easy way(without for loop) to input the function in to mathematica and draw the contour of f depending on x1 and x2?

Thanks.

f[x1_, x2_] := \!$$\*UnderoverscriptBox[\(\[Sum]$$, $$i = 1$$, $$10$$]$$\*UnderoverscriptBox[\(\[Sum]$$, $$j = 1$$, $$10$$]$$\*UnderoverscriptBox[\(\[Sum]$$, $$k = 1$$, $$10$$]$$\*UnderoverscriptBox[\(\[Sum]$$, $$l = 1$$, $$10$$]c[[i]] c[[j]] c[[k]] c[[l]]
\*SuperscriptBox[$$E$$, $$\((\[Alpha][[ i]] + \[Alpha][[j]] x1)$$ + $$(\[Alpha][[ k]] + \[Alpha][[l]] x2)$$\)]\)\)\)\)