diff --git a/src/matrixlu.jl b/src/matrixlu.jl
index a528c7d..24f6fae 100644
--- a/src/matrixlu.jl
+++ b/src/matrixlu.jl
@@ -96,13 +96,19 @@ function rrLU{T}(A::AbstractMatrix{T}; leftorthogonal::Bool=true) where {T}
 end
 
 function swaprow!(lu::rrLU{T}, A::AbstractMatrix{T}, a, b) where {T}
-    lu.rowpermutation[[a, b]] = lu.rowpermutation[[b, a]]
-    A[[a, b], :] = A[[b, a], :]
+    lurp = lu.rowpermutation
+    lurp[a], lurp[b] = lurp[b], lurp[a]
+    @inbounds for j in axes(A, 2)
+        A[a, j], A[b, j] = A[b, j], A[a, j]
+    end
 end
 
 function swapcol!(lu::rrLU{T}, A::AbstractMatrix{T}, a, b) where {T}
-    lu.colpermutation[[a, b]] = lu.colpermutation[[b, a]]
-    A[:, [a, b]] = A[:, [b, a]]
+    lucp = lu.colpermutation
+    lucp[a], lucp[b] = lucp[b], lucp[a]
+    @inbounds for i in axes(A, 1)
+        A[i, a], A[i, b] = A[i, b], A[i, a]
+    end
 end
 
 function addpivot!(lu::rrLU{T}, A::AbstractMatrix{T}, newpivot) where {T}
@@ -111,9 +117,9 @@ function addpivot!(lu::rrLU{T}, A::AbstractMatrix{T}, newpivot) where {T}
     swapcol!(lu, A, k, newpivot[2])
 
     if lu.leftorthogonal
-        A[k+1:end, k] /= A[k, k]
+        A[k+1:end, k] ./= A[k, k]
     else
-        A[k, k+1:end] /= A[k, k]
+        A[k, k+1:end] ./= A[k, k]
     end
 
     # perform BLAS subroutine manually: A <- -x * transpose(y) + A
@@ -139,12 +145,12 @@ function _optimizerrlu!(
     reltol::Number=1e-14,
     abstol::Number=0.0
 ) where {T}
-    maxrank = min(maxrank, size(A)...)
+    maxrank = min(maxrank, size(A, 1), size(A, 2))
     maxerror = 0.0
     while lu.npivot < maxrank
         k = lu.npivot + 1
         newpivot = submatrixargmax(abs2, A, k)
-        lu.error = abs(A[newpivot...])
+        lu.error = abs(A[newpivot[1], newpivot[2]])
         # Add at least 1 pivot to get a well-defined L * U
         if (abs(lu.error) < reltol * maxerror || abs(lu.error) < abstol) && lu.npivot > 0
             break
@@ -153,8 +159,8 @@ function _optimizerrlu!(
         addpivot!(lu, A, newpivot)
     end
 
-    lu.L = tril(A[:, 1:lu.npivot])
-    lu.U = triu(A[1:lu.npivot, :])
+    lu.L = tril(@view A[:, 1:lu.npivot])
+    lu.U = triu(@view A[1:lu.npivot, :])
     if any(isnan.(lu.L))
         error("lu.L contains NaNs")
     end
@@ -271,16 +277,16 @@ function arrlu(
         I2 = setdiff(1:matrixsize[1], I0)
         lu.rowpermutation = vcat(I0, I2)
         L2 = _batchf(I2, J0)
-        cols2Lmatrix!(L2, lu.U[1:lu.npivot, 1:lu.npivot], leftorthogonal)
-        lu.L = vcat(lu.L[1:lu.npivot, 1:lu.npivot], L2)
+        cols2Lmatrix!(L2, (@view lu.U[1:lu.npivot, 1:lu.npivot]), leftorthogonal)
+        lu.L = vcat((@view lu.L[1:lu.npivot, 1:lu.npivot]), L2)
     end
 
     if size(lu.U, 2) < matrixsize[2]
         J2 = setdiff(1:matrixsize[2], J0)
         lu.colpermutation = vcat(J0, J2)
         U2 = _batchf(I0, J2)
-        rows2Umatrix!(U2, lu.L[1:lu.npivot, 1:lu.npivot], leftorthogonal)
-        lu.U = hcat(lu.U[1:lu.npivot, 1:lu.npivot], U2)
+        rows2Umatrix!(U2, (@view lu.L[1:lu.npivot, 1:lu.npivot]), leftorthogonal)
+        lu.U = hcat((@view lu.U[1:lu.npivot, 1:lu.npivot]), U2)
     end
 
     return lu
@@ -313,8 +319,17 @@ function cols2Lmatrix!(C::AbstractMatrix, P::AbstractMatrix, leftorthogonal::Boo
     end
 
     for k in axes(P, 1)
-        C[:, k] /= P[k, k]
-        C[:, k+1:end] -= C[:, k] * transpose(P[k, k+1:end])
+        C[:, k] ./= P[k, k]
+        # C[:, k+1:end] .-= C[:, k] * transpose(P[k, k+1:end])
+        x = @view C[:, k]
+        y = @view P[k, k+1:end]
+        C̃ = @view C[:, k+1:end]
+        @inbounds for j in eachindex(axes(C̃, 2), y)
+            for i in eachindex(axes(C̃, 1), x)
+                # update `C[:, k+1:end]`
+                C̃[i, j] -= x[i] * y[j]
+            end
+        end
     end
     return C
 end
@@ -327,8 +342,17 @@ function rows2Umatrix!(R::AbstractMatrix, P::AbstractMatrix, leftorthogonal::Boo
     end
 
     for k in axes(P, 1)
-        R[k, :] /= P[k, k]
-        R[k+1:end, :] -= P[k+1:end, k] * transpose(R[k, :])
+        R[k, :] ./= P[k, k]
+        # R[k+1:end, :] -= P[k+1:end, k] * transpose(R[k, :])
+        x = @view P[k+1:end, k]
+        y = @view R[k, :]
+        R̃ = @view R[k+1:end, :]
+        @inbounds for j in eachindex(axes(R̃, 2), y)
+            for i in eachindex(axes(R̃, 1), x)
+                # update R[k+1:end, :]
+                R̃[i, j] -= x[i] * y[j]
+            end
+        end
     end
     return R
 end
diff --git a/src/util.jl b/src/util.jl
index 5685cc1..af704e9 100644
--- a/src/util.jl
+++ b/src/util.jl
@@ -53,7 +53,7 @@ end
 
 function pushrandomsubset!(subset, set, n::Int)
     topush = randomsubset(setdiff(set, subset), n)
-    push!(subset, topush...)
+    append!(subset, topush)
     nothing
 end