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Make the pullback for squareroot more GPU friendly #448

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Merged
kshyatt merged 1 commit into from
Oct 15, 2026
Merged

Make the pullback for squareroot more GPU friendly #448

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10 changes: 4 additions & 6 deletions src/algorithms/contractions/ctmrg/characteristic_equations.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -280,12 +280,10 @@ function ChainRulesCore.rrule(
return C, squareroot_pullback
end
function _squareroot_pullback(C::AbstractMatrix)
Fdata = similar(C)
for j in axes(Fdata, 2), i in axes(Fdata, 1)
# Taking the diagonal only is okay, when dA is diagonal anyway: Fdata[i, i] = 1 / (2 * conj(C[i, i]))
Fdata[i, j] = 1 / conj(C[i, i] + C[j, j])
end
return Fdata
# Taking the diagonal only is okay, when dA is diagonal anyway: Fdata[i, i] = 1 / (2 * conj(C[i, i]))
Cd = diagview(C)
Cdt = transpose(Cd)
return @. 1 / conj(Cd + Cdt)
end

# take fourth root of diagonal TensorMap, but with complex non-diagonal adjoint
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