CODEWITHSUNDEEP
julia
physicophilic
physicophilic

Reputation: 251

Julia - exponentiating a matrix returned from another function

I have functions f1 and f2 returning matrices m1 and m2, which are calculated using Diagonal, Tridiagonal, SymTridiagonal from LinearAlgebra package.

In a new function f3 I try computing

j = m1 - m2*im
m3 = exp(j)

but this gives a Method error on computation unless I use j=Matrix(m1-m2*im), saying that no matching method for exp(::LinearAlgebra.Tridiagonal ...)

My question is how can I do this computation in the most optimal way? I am a total beginner in Julia.

Upvotes: 3

Views: 266

Answers (1)

Bogumił Kamiński
Bogumił Kamiński

Reputation: 69819

Unless you have a very special structure of j (i.e. if its exponential is sparse - which is unlikely) the best you can do AFAICT is to use a dense matrix as an input to exp:

m3 = LinearAlgebra.exp!([float(x) for x in Tridiagonal(dl, d, du)])

If you expect m3 to be sparse then I think currently there is no special algorithm implemented for that case in Julia.

Note that I use exp! to do operation in place and use a comprehension to make sure the argument to exp! is dense. As exp! expects LinearAlgebra.BlasFloat (that is Union{Complex{Float32}, Complex{Float64}, Float32, Float64}) I use float to make sure that elements of j are appropriately converted. Note that it might fail if you work with e.g. BigFloat or Float16 values - in this case you have to do an appropriate conversion to the expected types yourself.

Upvotes: 3

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