What is the idiomatic way to construct a full m×m or n×n identity matrix similar to a given m×n matrix A (static or not)? one(A*A') or one(A'*A) does the trick but is of course not what I want.

Do you really need one? Can’t you just sidestep the question with LinearAlgebra.I?

Yes, it is the initial value of a matrix-valued ODE and should be of the same type as later values.

One way is julia> using LinearAlgebra julia> A = rand(4,5); julia> diagm(0=>fill(1., size(A,1))) 4×4 Array{Float64,2}: 1.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 1.0 julia> diagm(0=>fill(1., size(A,2))) 5×5 Array{Float64,2}: 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.…

Thank you, that’s it (almost)! julia> A 5×4 Array{Float64,2}: 0.896177 0.0597406 0.611605 0.231433 0.119473 0.998269 0.0299731 0.947813 0.0465002 0.431471 0.321885 0.20422 0.641878 0.0221313 0.0604966 0.517904 0.958566 0.675325 0.0570553 0.603291 julia> typeof(A)(one(…

For static arrays it is unfortunately slightly different julia> similar_type(B, Size(size(B,1),size(B,1)))(I) 5×5 SArray{Tuple{5,5},Float64,2,25}: 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0

julia> using LinearAlgebra julia> A = rand(5,4); julia> copyto!(similar(A, size(A,1), size(A,1)), I) 5×5 Array{Float64,2}: 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 1.0

I don’t think this works for static matrixes: julia> using LinearAlgebra, StaticArrays julia> A = @SMatrix rand(5,4); julia> typeof(copyto!(similar(A, size(A,1), size(A,1)), I)) Array{Float64,2} because the generic copyto! is used. This is could be a bug in StaticArrays, but at the same time I su…

For this use-case it would be nice provide a second argument like Val(:Left) to one which allows to specify to take the left or a right multiplicative unit if they are not equal.

Similar identity matrix

General Usage

carstenbauer September 8, 2018, 7:50am 5

Another way would be Matrix(one(eltype(A))I, size(A,1), size(A,1)) I guess.

Topic		Replies	Views
Replacing normal arrays with static arrays New to Julia linearalgebra	6	1436	August 31, 2019
Similar MArray with different size General Usage question , package , staticarrays	7	537	June 18, 2023
Linear Algebra tricks? General Usage	28	2004	May 4, 2020
Symbolics - Identity matrices for beginners General Usage linearalgebra , symbolics	5	2041	August 31, 2021
Eye in julia 0.7 New to Julia	37	8118	March 23, 2018

Similar identity matrix

Related topics