[BUG]: UndefVarError: permuterows! not defined on Julia ≤ 1.10

[Ady0333]

Problem

The functions _forward_cholesky and _backward_cholesky call Base.permuterows! and Base.invpermuterows!, which do not exist in Julia 1.9 or 1.10.

Broken code:

function _forward_cholesky(A::AbstractMatrix, L::AbstractSparseMatrix, p::AbstractVector)
  Base.permuterows!(A, p)        # ❌ doesn't exist in Julia ≤ 1.10
  Ã = L' * A
  Base.invpermuterows!(A, p)     # ❌ doesn't exist in Julia ≤ 1.10
  return Ã
end

function _backward_cholesky(Ã::AbstractMatrix, L::AbstractSparseMatrix, p::AbstractVector)
  A = L' \ Ã
  Base.invpermuterows!(A, p)     # ❌ doesn't exist in Julia ≤ 1.10
  return A
end

Verification:

julia> VERSION
v"1.10.5"

julia> isdefined(Base, :permuterows!)
false

julia> isdefined(Base, :invpermuterows!)
false

These functions were introduced in Julia 1.11+, but Project.toml declares julia = "1.9" as the minimum supported version.

---

Impact

Who is affected: Everyone running GridapROMs on Julia 1.9 or 1.10 (including the LTS 1.10 version) who uses energy-norm POD.

What breaks:

• Every ROM workflow using energy-norm weighted POD crashes with UndefVarError: permuterows! not defined
• The call chain: reduced_basis(PODReduction, feop, s) → tpod(A, X) → _cholesky_decomp(X) → _forward_cholesky → crash
• RBSteady tests: Poisson, Stokes, Navier-Stokes all fail
• RBTransient workflows using energy norms also affected

Why this is critical: Energy-norm POD is the default, standard ROM approach in FEM-based reduced-order modeling. This breaks the primary workflow of the package for anyone not on Julia 1.11+.

---

Proposed Fix

Replace with Julia 1.9+ compatible operations using array indexing:

function _forward_cholesky(A::AbstractMatrix, L::AbstractSparseMatrix, p::AbstractVector)
  Ã = L' * A[p, :]
  return Ã
end

function _backward_cholesky(Ã::AbstractMatrix, L::AbstractSparseMatrix, p::AbstractVector)
  Ap = L' \ Ã
  A = similar(Ap)
  A[p, :] = Ap
  return A
end

This is numerically equivalent to the original intent:

• A[p, :] selects rows in permutation order (equivalent to permuterows! + use)
• A[p, :] = Ap undoes the permutation (equivalent to invpermuterows!)
• Uses only Base operations available since Julia 1.0

[nichomueller]

Hi @Ady0333 , thanks again for your help. The fix you suggest allocates a lot of memory, and should be avoided. What I did is copying the functions permuterows! and invpermuterows! from Base, so they'll always be available within GridapROMs, independently of the julia version.

[Ady0333]

Thanks @nichomueller! That makes sense... copying the functions avoids the allocation overhead. Thankyou for taking the time to implement the more efficient solution!