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[documentation] Improve the docstring of SimpleStats #917

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40 changes: 24 additions & 16 deletions src/krylov_stats.jl
Original file line number Diff line number Diff line change
Expand Up @@ -7,15 +7,16 @@ import Base.copyto!
abstract type KrylovStats{T} end

"""
Type for statistics returned by the majority of Krylov solvers, the attributes are:
- niter
- solved
- inconsistent
- residuals
- Aresiduals
- Acond
- timer
- status
Type for storing statistics returned by the majority of Krylov solvers.
The fields are as follows:
- `niter`: The total number of iterations completed by the solver;
- `solved`: Indicates whether the solver successfully reached convergence (`true` if solved, ``false` otherwise);
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- `solved`: Indicates whether the solver successfully reached convergence (`true` if solved, ``false` otherwise);
- `solved`: Indicates whether the solver successfully reached convergence (`true` if solved, `false` otherwise);

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Also, convergence according to which criterion? A tolerance I assume?

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@amontoison amontoison Oct 29, 2024

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The answer is quite complex. It depends which shopping condition is triggered.
It could be also related to the callback.

I need to document that since a long time too: #552

- `inconsistent`: Flags whether the system was detected as inconsistent (i.e., when `b` is not in the range of `A`);
- `residuals`: A vector containing the residual norms at each iteration;
- `Aresiduals`: A vector of `Aᴴ`-residual norms at each iteration;
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What is Aᴴ?

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@amontoison amontoison Oct 29, 2024

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The adjoint of A Guillaume.
A^T is the transpose and A^H the conjugate hermitian.
In the real case A^H are A^T are the same matrices.

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My bad, I'm more used to A' or A* for the adjoint, hence my surprise

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I will use A'. I probably expected users to know too many concepts of linear algebra (A^H, consistent, indefinite, singular, singular, dual, etc...).

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Some of those were probably explained elsewhere in the docs, like A^H, but yeah the point of all my review comments was getting some clarification in the stats docstring itself.

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- `Acond`: An estimate of the condition number of matrix `A`.
- `timer`: The elapsed time (in seconds) taken by the solver to complete all iterations;
- `status`: A string indicating the outcome of the solve, providing additional details beyond `solved`.
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Can you give an example? What are its possible values?

"""
mutable struct SimpleStats{T} <: KrylovStats{T}
niter :: Int
Expand Down Expand Up @@ -47,7 +48,8 @@ function copyto!(dest :: SimpleStats, src :: SimpleStats)
end

"""
Type for statistics returned by LSMR. The attributes are:
Type for storing statistics returned by LSMR.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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Same for the other more sophisticated stats, so that you don't need to document every field again

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What is xNorm here?

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The norm of the solution x.
You can compute it cheaply for many methods because the Krylov basis is orthonormal.

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okay, we should probably explain it here then

- niter
- solved
- inconsistent
Expand Down Expand Up @@ -96,7 +98,8 @@ function copyto!(dest :: LsmrStats, src :: LsmrStats)
end

"""
Type for statistics returned by CG-LANCZOS, the attributes are:
Type for storing statistics returned by CG-LANCZOS.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What is indefinite here?

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@amontoison amontoison Oct 29, 2024

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It means that the matrix is indefinite.
A matrix is indefinite if it has positive and negative eigenvalues.

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okay, we should probably explain it here or in a high-level preamble

- niter
- solved
- residuals
Expand Down Expand Up @@ -134,7 +137,8 @@ function copyto!(dest :: LanczosStats, src :: LanczosStats)
end

"""
Type for statistics returned by CG-LANCZOS with shifts, the attributes are:
Type for storing statistics returned by CG-LANCZOS-SHIFT and CGLS-LANCZOS-SHIFT.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What is indefinite here?

- niter
- solved
- residuals
Expand Down Expand Up @@ -174,7 +178,8 @@ function copyto!(dest :: LanczosShiftStats, src :: LanczosShiftStats)
end

"""
Type for statistics returned by SYMMLQ, the attributes are:
Type for storing statistics returned by SYMMLQ.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What are residualscg, errors and errorscg here?

- niter
- solved
- residuals
Expand Down Expand Up @@ -221,7 +226,8 @@ function copyto!(dest :: SymmlqStats, src :: SymmlqStats)
end

"""
Type for statistics returned by adjoint systems solvers BiLQR and TriLQR, the attributes are:
Type for storing statistics returned by adjoint systems solvers BiLQR and TriLQR.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What do the primal and dual suffixes mean here?

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You solve two systems here Ax = b and A'y = c. The primal refers to the first system while the dual refers to the second one.

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maybe this docstring could link to an explanation of the algorithm itself for these details

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It's just that you checked the docstring in the wrong way.
I don't think any user wants to understand how to use a result before knowing how to obtain it. 😉

Nobody will ever use AdjointStats without previously calling bilqr and trilqr, which explain everything and that gives a pointer to this structure: https://jso.dev/Krylov.jl/dev/solvers/as/

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fair enough

- niter
- solved_primal
- solved_dual
Expand Down Expand Up @@ -258,7 +264,8 @@ end


"""
Type for statistics returned by the LNLQ method, the attributes are:
Type for storing statistics returned by the LNLQ method.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What do the error_ fields mean here?

- niter
- solved
- residuals
Expand Down Expand Up @@ -298,7 +305,8 @@ function copyto!(dest :: LNLQStats, src :: LNLQStats)
end

"""
Type for statistics returned by the LSLQ method, the attributes are:
Type for storing statistics returned by the LSLQ method.
The fields are as follows:
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The fields are as follows:
The fields are as follows (see [`Krylov.SimpleStats`](@ref)):

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What are the new fields here?

- niter
- solved
- inconsistent
Expand Down
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