inconsistent behaviour of * and \ for non-square matrices:

[Jutho]

I did not want to add this issue to the Number/Matrix issue, as it is of a different nature and might get lost in the long discussion going on over there.

Consider the following:
vec=rand(10)
mat=reshape(vec,(10,1))

None of this should work: vec * vec, mat_mat, vec_mat mat_vec
(at least not from an algebraic point of view, I am not so familiar with the broadcasting rules but in relation to the other discussion I would favour to explicitly require the use of ._ for broadcasting)
The first (vector vector multiplication) gives a no method error
The second (matrix matrix multiplication) gives a dimension mismatch error
The third (vector matrix multiplication) gives a dimension mismatch
The fourth, however, computes something. It took me a second before realising what was computed exactly, but it seems to be mat * vec[1]. I don't think this falls under the scope of broadcasting.

Even knowing that A\B is generalised to non-square matrices A if B has the same number of columns as A (in the least square sense), the following should still not exist: vec' \ vec and vec \ vec'
Yet, vec' \ vec = vec' \ mat produces a vector of length 10
(I do not immediately see what is calculated)
vec \ vec' = mat \ vec' produces:
** On entry to DORMQR parameter number 10 had an illegal value
ERROR: ArgumentError("invalid argument JuliaLang/julia#10 to LAPACK call")

[JHonaker]

This is interesting. I think this problems stems from a difference between a 10-element array and a 10x1 array. After a short testing session, it seems if you use mat*vec'' (which casts vec as a 10x1 array instead of a 10-element array), you get a dimension mismatch error. I'm fairly new to Julia, but what exactly is the different between a 10-element and a 10x1 array? Conceptually nothing, but what files should I/we be investigating for this?

[andreasnoack]

I missed this issue, but I have submitted a fix in #85.

@JohnnyAppleDev The easiest way to find the relevant place in the source is to put the macro @which before the function call, e.g. @which mat*vec

[andreasnoack]

Fixed by #85

[JHonaker]

@andreasnoackjensen Thanks for the tip and the fix.

[Jutho]

Thanks indeed