diff --git a/src/ConstLinearLayer.jl b/src/ConstLinearLayer.jl
index 5dcbb0d..d03ccd6 100644
--- a/src/ConstLinearLayer.jl
+++ b/src/ConstLinearLayer.jl
@@ -2,15 +2,11 @@ import ChainRulesCore: rrule
 using LuxCore
 using LuxCore: AbstractExplicitLayer
 
-struct ConstLinearLayer <: AbstractExplicitLayer # where {in_dim,out_dim,T}
-    op #::AbstractMatrix{T}  
-    position::Union{Vector{Int64}, UnitRange{Int64}}
+struct ConstLinearLayer <: AbstractExplicitLayer
+    op
 end
 
-ConstLinearLayer(op) = ConstLinearLayer(op,1:size(op,2))
-# ConstLinearLayer(op, pos::Union{Vector{Int64}, UnitRange{Int64}}) = ConstLinearLayer(op,pos)
-
-(l::ConstLinearLayer)(x::AbstractVector) = l.op * x[l.position]
+(l::ConstLinearLayer)(x::AbstractVector) = l.op * x[1:size(l.op,2)]
 
 (l::ConstLinearLayer)(x::AbstractMatrix) = begin
     Tmp = l(x[1,:])
@@ -20,6 +16,9 @@ ConstLinearLayer(op) = ConstLinearLayer(op,1:size(op,2))
     return Tmp'
  end
 
+ (l::ConstLinearLayer)(x::AbstractArray,ps,st) = (l(x), st)
+
+ # NOTE: the following rrule is kept because there is a issue with SparseArray
 function rrule(::typeof(LuxCore.apply), l::ConstLinearLayer, x::AbstractVector)
     val = l(x)
     function pb(A)
@@ -28,20 +27,10 @@ function rrule(::typeof(LuxCore.apply), l::ConstLinearLayer, x::AbstractVector)
     return val, pb
 end
 
-(l::ConstLinearLayer)(x::AbstractArray,ps,st) = (l(x), st)
-
 function rrule(::typeof(LuxCore.apply), l::ConstLinearLayer, x::AbstractArray,ps,st)
     val = l(x,ps,st)
     function pb(A)
         return NoTangent(), NoTangent(), l.op' * A[1], (op = A[1] * x',), NoTangent()
     end
     return val, pb
-end
-
-# function rrule(::typeof(LuxCore.apply), l::ConstLinearLayer, x::AbstractMatrix, ps, st)
-#     val = l(x, ps, st)
-#     function pb(A)
-#        return NoTangent(), NoTangent(), l.op' * A[1], (op = A[1] * x',), NoTangent()
-#     end
-#     return val, pb
-#  end
\ No newline at end of file
+end
\ No newline at end of file
diff --git a/src/builder.jl b/src/builder.jl
index 2bbab0c..c215411 100644
--- a/src/builder.jl
+++ b/src/builder.jl
@@ -261,7 +261,6 @@ function equivariant_model(spec_nlm, radial::Radial_basis, L::Int64; categories=
       C = _rpi_A2B_matrix(cgen, spec_nlm)
    end
    
-   #TODO:make use [ C[i], pos[i] ] to generate another sparse matrix so that...
    l_sym = islong ? Lux.Parallel(nothing, [ConstLinearLayer(new_sparse_matrix(C[i],pos[i])) for i = 1:L+1]... ) : ConstLinearLayer(C)
    # C - A2Bmap
    luxchain = append_layer(luxchain_tmp, l_sym; l_name = :BB)
@@ -278,7 +277,7 @@ function new_sparse_matrix(C,pos)
    for i = 1:size(C,1)
       C_new[i,pos] = C[i,:]
    end
-   return C_new
+   return sparse(C_new)
 end
 
 # more constructors equivariant_model