How do I pass extra known parameters to arrayfun?

For example, if I want to find the position in the corresponding array b from each element of array a, how should I write the code?

a = [1,2,3]; 
b = [2,1,1,3,1,2];
idx = arrayfun(@(x,b)find(x==b),a,b)

Error using arrayfun
All of the input arguments must be of the same size and shape.
Previous inputs had size 3 in dimension 2. Input #3 has size 6

The desired idx outcome is：{[2,3,5],[1,6],[4]}

Answer 1

[cui,xingxing]

I get the answer:

a = [1,2,3]; 
b = [2,1,1,3,1,2];
idx = arrayfun(@(x)find(x==b),a,'UniformOutput',false)

idx = 1×3 cell array
    {[2 3 5]}    {[1 6]}    {[4]}