Given the code

```
foo(x,y) = x+y
xvec = range(0,1,length=5)
yvec = range(0,1,length=5)
fvec = vec(foo.(xvec,yvec'))
```

Q1: how to find indices on fvec that correspond to start/end point of xvec/yvec ?

Q2: how to overwrite values of fvec that correspond to start/end point of xvec/yvec ?

Thx!

Vectors are column vectors in Julia. Hence, in `foo.(xvec, yvec')`

, the first column correspond to the first element of `xvec`

, and the first row correspond to the first element of `yvec`

.

Since matrices are column-ordered in Julia, that means the indices `1:5`

correspond to the start point of `xvec`

, `21:25`

to the last point, `1:5:21`

the first point of `yvec`

, `5:5:25`

the last point of `yvec`

.

To overwrite them with `19`

, you could do e.g. `fvec[1:5:21] .= 19`