This caught me by surprise: julia> ones(10)*ones(1,10) ERROR: DimensionMismatch("Cannot left-multiply a matrix by a vector") Stacktrace: [1] *(::Array{Float64,1}, ::Array{Float64,2}) at ./linalg/rowvector.jl:157 Is this a bug, or intentional? (I don’t see why this wouldn’t make sense…)

Maybe because of http://docs.julialang.org/en/latest/stdlib/linalg.html#Base.LinAlg.RowVector and related to https://github.com/JuliaLang/julia/pull/19670 ?

Yes I believe that is the cause, I’m more wondering about the why? It seems to me that the multiplication above should still work as the dimensions are consistent, unless Vector no longer means column vector (in which case, I would expect a type ColumnVector)

I think it was discussed in one of the comments, for instance here .

That’s a very long discussion, I didn’t see this issue addressed . Note that this issue is completely independent of whether a RowVector exists. It’s just a matter of a column vector times a 1 x matrix is mathematically well-defined.

OK I’ve created an issue: https://github.com/JuliaLang/julia/issues/20389

Maybe this is just a broadcast operation? julia> ones(3).*ones(1,3) 3×3 Array{Float64,2}: 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

To me, the question is in reverse - why did this method exist in v0.5? The (only) reason is it was a way of obtaining the outer product of two vectors. You can now do vector * rowvector for this. In fact, this is still a (specialized) method of *(::AbstractVector, ::AbstractMatrix). Otherwise vect…

Maybe this is just a broadcast operation? The implementation is precisely this.

[image] andyferris: Otherwise vector * matrix doesn’t make too much sense If we view a vector as a 1-column matrix, then vector * (1-row matrix) makes perfect sense in standard linear algebra… (I agree that there is some tension between this viewpoint and viewing vectors as living in some ki…

Vector*matrix in 0.6

General Usage

mzaffalon February 2, 2017, 10:34am 6

Agreed. It seems that this is such a fundamental operation that it should be in the test suite.

Topic		Replies	Views
Why does Julia support `::Vector * ::Matrix`? General Usage question , linearalgebra	7	601	December 9, 2023
Matrix multiplication - inconsistent behaviour General Usage question	50	3204	May 16, 2020
Vector vs Column vector New to Julia question	13	9746	February 21, 2020
What is wrong with [1.] * [1.]? New to Julia	9	781	November 3, 2018
Array/Vector multiplication for single element arrays New to Julia question	8	10121	May 13, 2020

Vector*matrix in 0.6

Related topics