added multiplication operator

Author: rittermarc

src/abstracttensortrain.jl

@@ -218,6 +218,6 @@ Addition of two tensor trains. If `c = a + b`, then `c(v) ≈ a(v) + b(v)` at ea
 
 See also: [`add`](@ref)
 """
-function (+)(lhs::AbstractTensorTrain{V}, rhs::AbstractTensorTrain{V}) where {V}
+function Base.:+(lhs::AbstractTensorTrain{V}, rhs::AbstractTensorTrain{V}) where {V}
     return add(lhs, rhs)
 end

src/tensortrain.jl

@@ -125,6 +125,36 @@ function compress!(
 end
 
 
+function multiply!(tt::TensorTrain{V, N}, a) where {V, N}
+    tt.sitetensors[end] .= tt.sitetensors[end] .* a
+    nothing
+end
+
+function multiply!(a, tt::TensorTrain{V, N}) where {V, N}
+    tt.sitetensors[end] .= a .* tt.sitetensors[end]
+    nothing
+end
+
+function multiply(tt::TensorTrain{V, N}, a)::TensorTrain{V, N} where {V, N}
+    tt2 = deepcopy(tt)
+    multiply!(tt2, a)
+    return tt2
+end
+
+function multiply(a, tt::TensorTrain{V, N})::TensorTrain{V, N} where {V, N}
+    tt2 = deepcopy(tt)
+    multiply!(a, tt2)
+    return tt2
+end
+
+function Base.:*(tt::TensorTrain{V, N}, a)::TensorTrain{V, N} where {V, N}
+    return multiply(tt, a)
+end
+
+function Base.:*(a, tt::TensorTrain{V, N})::TensorTrain{V, N} where {V, N}
+    return multiply(a, tt)
+end
+
 """
 Fitting data with a TensorTrain object.
 This may be useful when the interpolated function is noisy.

test/test_tensortrain.jl

@@ -119,7 +119,7 @@ end
     @test [TCI.evaluate(ttopt, idx) for (idx, v) in zip(indexsets, values)] ≈ values
 end
 
-@testset "tensor train addition" for T in [Float64, ComplexF64]
+@testset "tensor train addition and multiplication" for T in [Float64, ComplexF64]
     Random.seed!(10)
     localdims = [2, 2, 2]
     linkdims = [1, 2, 3, 1]
@@ -134,6 +134,9 @@ end
     ttadd2 = tt1 + tt2
     @test ttadd2.(indices) ≈ [tt1(v) + tt2(v) for v in indices]
 
+    tt1mul = 1.6 * tt1
+    @test tt1mul.(indices) ≈ 1.6 .* tt1.(indices)
+
     ttshort = TCI.TensorTrain{T,3}([randn(T, linkdims[n], localdims[n], linkdims[n+1]) for n in 1:L-1])
     @test_throws DimensionMismatch TCI.add(tt1, ttshort)