Make an example with two inputs from which you want to change it. Since you claim that your function is really complex, write it to a file with the name complicated.mthat we save in the Matlab path.
function out = complicated(v1,v2,x)
out = v1*x-v2*x.^2;
, v1 v2
figure,hold on
for v1 = 1:5
for v2 = 1:5
%
myFun = @(x)complicated(v1,v2,x);
%
fzero(myFun,1)
%
plot(-5:0.1:5,myFun(-5:0.1:5))
end
end