灰常急~~~~求助：用matlab的fmincon做极大似然估计

求助论坛里的各位高手：
我想用matlab的fmincon做极大似然估计，已知某分布的密度函数，求出其似然函数为：
f=-n(log(delta)*(1/x(1))-gammaln(1+1/x(1)))+(delta*sum/beta^x(1));
其中delta = (2*x(2)^x(1)*(1-x(2))^x(1))/(x(2)^x(1)+(1-x(2))^x(1));
for i = 1:length(a),
sum = 0;
for i = 1:n ;
sum = ( abs(a(i)) ) ^ x(1) + sum;
end
主要程序如下：
function f = myfun2(x,a)
banana = @(x)myfun2(x,a1);
[x,fval,exitflag] = fmincon(banana,[6;0.6],[],[],[],[],[0,0],[3,1],[],options);

但是运行后老出现以下错误，请问高手，这是怎么回事？问题出在哪？
??? Error using ==> fmincon at 504
FMINCON cannot continue because user supplied objective function failed with the following error:
Subscript indices must either be real positive integers or logicals.
Error in ==> MLE at 21
[x,fval] = fmincon(banana,[6;0.6],[],[],[],[],[0,0],[3,1],[],options);


灰常灰常着急，望赐教，谢谢！！！