[NDTensors] [BUG] Fix bug in in-place contract (#1158)

NDTensors/src/dense/tensoralgebra/contract.jl

@@ -344,9 +344,8 @@ function _contract!(
 ) where {El,NC,NA,NB}
   tA = 'N'
   if props.permuteA
-    pA = NTuple{NA,Int}(props.PA)
     #@timeit_debug timer "_contract!: permutedims A" begin
-    @strided Ap = permutedims(AT, pA)
+    @strided Ap = permutedims(AT, props.PA)
     #end # @timeit
     AM = transpose(reshape(Ap, (props.dmid, props.dleft)))
   else
@@ -360,9 +359,8 @@ function _contract!(
 
   tB = 'N'
   if props.permuteB
-    pB = NTuple{NB,Int}(props.PB)
     #@timeit_debug timer "_contract!: permutedims B" begin
-    @strided Bp = permutedims(BT, pB)
+    @strided Bp = permutedims(BT, props.PB)
     #end # @timeit
     BM = reshape(Bp, (props.dmid, props.dright))
   else
@@ -377,10 +375,9 @@ function _contract!(
   if props.permuteC
     # if we are computing C = α * A B + β * C
     # we need to make sure C is permuted to the same 
-    # ordering as A B
+    # ordering as A B which is the inverse of props.PC
     if β ≠ 0
-      pC = NTuple{NB,Int}(props.PC)
-      CM = reshape(permutedims(CT, pC), (props.dleft, props.dright))
+      CM = reshape(permutedims(CT, invperm(props.PC)), (props.dleft, props.dright))
     else
       # Need to copy here since we will be permuting
       # into C later  
@@ -399,11 +396,10 @@ function _contract!(
   mul!(CM, AM, BM, El(α), El(β))
 
   if props.permuteC
-    pC = NTuple{NC,Int}(props.PC)
     Cr = reshape(CM, props.newCrange)
     # TODO: use invperm(pC) here?
     #@timeit_debug timer "_contract!: permutedims C" begin
-    @strided CT .= permutedims(Cr, pC)
+    @strided CT .= permutedims(Cr, props.PC)
     #end # @timeit
   end
 

test/base/test_contract.jl

@@ -245,8 +245,8 @@ digits(::Type{T}, i, j, k) where {T} = T(i * 10^2 + j * 10 + k)
       A = randomITensor(T, (j, i))
       B = randomITensor(T, (j, k, l, α))
       C = ITensor(zero(T), (i, k, α, l))
-      ITensors.contract!(C, A, B, 1.0, 0.0)
-      ITensors.contract!(C, A, B, 1.0, 1.0)
+      ITensors.contract!(C, B, A, 1.0, 0.0)
+      ITensors.contract!(C, B, A, 1.0, 1.0)
       D = A * B
       D .+= A * B
       @test C ≈ D