diff --git a/Project.toml b/Project.toml
index 420c59a..c52805f 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "PartitionedMPSs"
 uuid = "17ce1de9-5131-45e3-8a48-9723b6e2dc23"
 authors = ["Hiroshi Shinaoka <h.shinaoka@gmail.com> and contributors"]
-version = "0.5.3"
+version = "0.5.4"
 
 [deps]
 Coverage = "a2441757-f6aa-5fb2-8edb-039e3f45d037"
diff --git a/src/partitionedmps.jl b/src/partitionedmps.jl
index 6a00ba0..10b265f 100644
--- a/src/partitionedmps.jl
+++ b/src/partitionedmps.jl
@@ -112,6 +112,21 @@ Add two PartitionedMPS objects.
 If the two projects have the same projectors in the same order, the resulting PartitionedMPS will have the same projectors in the same order.
 By default, we use `directsum` algorithm to compute the sum and no truncation is performed.
 """
+function Base.:+(
+    partmpss::PartitionedMPS...;
+    alg="directsum",
+    cutoff=0.0,
+    maxdim=typemax(Int),
+    coeffs=ones(length(partmpss)),
+    kwargs...,
+)::PartitionedMPS
+    result = PartitionedMPS()
+    for (coeff, partmps) in zip(coeffs, partmpss)
+        result = +(result, coeff * partmps; alg, cutoff, maxdim, kwargs...)
+    end
+    return result
+end
+
 function Base.:+(
     a::PartitionedMPS,
     b::PartitionedMPS;
@@ -182,6 +197,7 @@ function truncate(
     cutoff=default_cutoff(),
     maxdim=default_maxdim(),
     use_adaptive_weight=true,
+    maxrefinement=4,
     kwargs...,
 )::PartitionedMPS
     norm2 = [LinearAlgebra.norm(v)^2 for v in values(obj)]
@@ -190,7 +206,7 @@ function truncate(
 
     compressed = obj
 
-    while true
+    for _ in 1:maxrefinement
         compressed = PartitionedMPS([
             truncate(v; cutoff=cutoff * w, maxdim, kwargs...) for
             (v, w) in zip(values(obj), weights)
@@ -200,7 +216,7 @@ function truncate(
             break
         end
 
-        weights .*= cutoff / actual_error # Adjust weights
+        weights .*= min(cutoff / actual_error, 0.5) # Adjust weights
     end
 
     return compressed
diff --git a/src/projector.jl b/src/projector.jl
index 4b4beda..6879241 100644
--- a/src/projector.jl
+++ b/src/projector.jl
@@ -43,6 +43,7 @@ end
 projectedinds(p::Projector) = p.data
 
 Base.getindex(p::Projector, inds) = p.data[inds]
+Base.getindex(p::Projector, ind, default) = get(p.data, ind, default)
 Base.keys(p::Projector) = keys(p.data)
 
 function Base.iterate(obj::Projector, state)
diff --git a/src/subdomainmps.jl b/src/subdomainmps.jl
index a74eb1e..431c531 100644
--- a/src/subdomainmps.jl
+++ b/src/subdomainmps.jl
@@ -66,6 +66,18 @@ function project(projΨ::SubDomainMPS, projector::Projector)::Union{Nothing,SubD
     )
 end
 
+function project(
+    projΨ::SubDomainMPS, pairs::Vararg{Pair{Index{T},Int}}
+)::Union{Nothing,SubDomainMPS} where {T}
+    return project(projΨ, Projector(pairs...))
+end
+
+function project(
+    Ψ::AbstractMPS, pairs::Vararg{Pair{Index{T},Int}}
+)::Union{Nothing,SubDomainMPS} where {T}
+    return project(Ψ, Projector(pairs...))
+end
+
 function project(Ψ::AbstractMPS, projector::Projector)::Union{Nothing,SubDomainMPS}
     return project(SubDomainMPS(Ψ), projector)
 end
diff --git a/test/partitionedmps_tests.jl b/test/partitionedmps_tests.jl
index 67c367c..cdd1deb 100644
--- a/test/partitionedmps_tests.jl
+++ b/test/partitionedmps_tests.jl
@@ -65,6 +65,20 @@ import PartitionedMPSs: PartitionedMPSs, Projector, project, SubDomainMPS, Parti
         @test MPS((a + b) + 2 * (b + a)) ≈ 3 * Ψ rtol = 1e-13
     end
 
+    @testset "add" begin
+        Random.seed!(1234)
+        N = 3
+        d = 10
+        sites = [Index(d, "x=$n") for n in 1:N]
+        Ψ = MPS(collect(_random_mpo([[s] for s in sites])))
+
+        projectors = [Projector(sites[1] => d_) for d_ in 1:d]
+        coeffs = rand(length(projectors))
+        prjΨs = [project(Ψ, p) for p in projectors]
+
+        @test MPS(+([PartitionedMPS(x) for x in prjΨs]...; coeffs=coeffs)) ≈ +([c * MPS(x) for (c, x) in zip(coeffs, prjΨs)]...; alg="directsum")
+    end
+
     @testset "truncate" begin
         for seed in [1, 2, 3, 4, 5]
             Random.seed!(seed)