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Fix scaling unit triangular matrices #1346

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Merged
merged 1 commit into from
May 11, 2025
Merged

Fix scaling unit triangular matrices #1346

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31 changes: 13 additions & 18 deletions src/triangular.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1323,6 +1323,15 @@ end
# Generic routines #
####################

function _set_diag!(B::UpperOrLowerTriangular, x)
# get a mutable array to modify the diagonal
Bm = parent(B) isa StridedArray ? B : copy!(similar(B), B)
for i in diagind(Bm.data, IndexStyle(Bm.data))
Bm.data[i] = x
end
Bm
end

for (t, unitt) in ((UpperTriangular, UnitUpperTriangular),
(LowerTriangular, UnitLowerTriangular))
tstrided = t{<:Any, <:StridedMaybeAdjOrTransMat}
Expand All @@ -1336,10 +1345,7 @@ for (t, unitt) in ((UpperTriangular, UnitUpperTriangular),

function (*)(A::$unitt, x::Number)
B = $t(A.data)*x
for i in axes(A, 1)
B.data[i,i] = x
end
return B
_set_diag!(B, oneunit(eltype(A)) * x)
end

(*)(x::Number, A::$t) = $t(x*A.data)
Expand All @@ -1351,10 +1357,7 @@ for (t, unitt) in ((UpperTriangular, UnitUpperTriangular),

function (*)(x::Number, A::$unitt)
B = x*$t(A.data)
for i in axes(A, 1)
B.data[i,i] = x
end
return B
_set_diag!(B, x * oneunit(eltype(A)))
end

(/)(A::$t, x::Number) = $t(A.data/x)
Expand All @@ -1366,11 +1369,7 @@ for (t, unitt) in ((UpperTriangular, UnitUpperTriangular),

function (/)(A::$unitt, x::Number)
B = $t(A.data)/x
invx = inv(x)
for i in axes(A, 1)
B.data[i,i] = invx
end
return B
_set_diag!(B, oneunit(eltype(A)) / x)
end

(\)(x::Number, A::$t) = $t(x\A.data)
Expand All @@ -1382,11 +1381,7 @@ for (t, unitt) in ((UpperTriangular, UnitUpperTriangular),

function (\)(x::Number, A::$unitt)
B = x\$t(A.data)
invx = inv(x)
for i in axes(A, 1)
B.data[i,i] = invx
end
return B
_set_diag!(B, x \ oneunit(eltype(A)))
end
end
end
Expand Down
10 changes: 10 additions & 0 deletions test/triangular.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -934,4 +934,14 @@ end
end
end

@testset "block unit triangular scaling" begin
m = SizedArrays.SizedArray{(2,2)}([1 2; 3 4])
U = UnitUpperTriangular(fill(m, 4, 4))
M = Matrix{eltype(U)}(U)
@test U/2 == M/2
@test 2\U == 2\M
@test U*2 == M*2
@test 2*U == 2*M
end

end # module TestTriangular