(Edit: I answered my question somewhat and posted it at the end)
I recently ran into a bug in my code in which Julia gave an error when
computing the matrix inverse of what I thought was a 1x1 matrix. I looked
into it, and it looks like my sequence of matrix multiplications resulted
in a 5x5 matrix being converted into a 1 dimensional array. I'm not really
sure why this happens. Here's an example:
A = rand(2,2)
B = rand(2,1)
B'*A*B
1x1 Array{Float64,2}:
0.836342
This is fine. But,
R = [0;1]
R'*A*R
1-element Array{Float64,1}:
0.921516
I think the problem is that B is explicitly defined as a 2 dimensional
array. On the other hand, R is 2-element Array{Int64,1}: , a 1 dimensional
array. This is a problem because
(R'*A*R)^(-1)
DomainError
It looks like, in Julia, I have to be very careful about combining
1-dimensional vectors and 2 dimensional matrices. Is there a better way to
do this? Also, when constructing a matrix(or vector) by hand, as in R =
[0;1], can I force it to be 2 dimensional?
Edit: I just sort of answered my own question, but I'll post this anyway in
case anyone else has this question, or if there are any comments.
If I define R as
R = [0 1]'
2x1 Array{Int64,2}:
0
1
then there is no issue.
