[julia-users] efficiently add floats to a particular element of a vector

[Jeff]

Adding floats to an element of a vector takes about twice as long as adding 
float to a variable. For example,

```
    val = zeros(1)
    for i in 1:10000000
        val[1] += 9.
    end
```
finishes in 0.034 seconds whereas
```
    a = 0.
    for i in 1:10000000
        a += 9.
    end 
```
take just 0.015 seconds.

Is the former block of code looking up the address in memory of `val[1]` at 
every iteration? Or does have something to do with `a` being stack 
allocated whereas `val` is heap allocated?

Is there a way to add floats to a particular index of a vector without 
incurring runtime overhead, if I know at compile time what the index is?

Thanks!