Find indices of boundary nodes

General Usage
1

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!

2

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

3

Or use LinearIndices.