How can I increase the efficiency in this algorithm?

I have an algorithm called MinDistance that determines the distance between the two closest elements in an array. I need to make it more efficient.

Here is the algorithm, written in pseudocode:

MinDistance(A[0...n-1]
dmin <-- infinity
for i <--- 0 to n - 1 do
    for j <--- 0 to n - 1 do
        if i does not equal j and |A|i| - A|j|| < dmin
           dmin <--- |A|i| - A|j||
return dmin

To me, this feels like it's in its most efficient form, but I'm wrong. Can you help?

Thank you very much.