diff --git a/lib/NonlinearProblemLibrary/Project.toml b/lib/NonlinearProblemLibrary/Project.toml
index 8c8c9ba..7681d54 100644
--- a/lib/NonlinearProblemLibrary/Project.toml
+++ b/lib/NonlinearProblemLibrary/Project.toml
@@ -7,13 +7,17 @@ LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 SciMLBase = "0bca4576-84f4-4d90-8ffe-ffa030f20462"
 
 [compat]
+AllocCheck = "0.2"
 Aqua = "0.8"
 LinearAlgebra = "1.6"
 SciMLBase = "2"
+Test = "1"
 julia = "1.10"
 
 [extras]
+AllocCheck = "9b6a8646-10ed-4001-bbdc-1d2f46dfbb1a"
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Aqua"]
+test = ["AllocCheck", "Aqua", "Test"]
diff --git a/lib/NonlinearProblemLibrary/src/NonlinearProblemLibrary.jl b/lib/NonlinearProblemLibrary/src/NonlinearProblemLibrary.jl
index 7b6cdf1..cf19775 100644
--- a/lib/NonlinearProblemLibrary/src/NonlinearProblemLibrary.jl
+++ b/lib/NonlinearProblemLibrary/src/NonlinearProblemLibrary.jl
@@ -429,16 +429,17 @@ p22_dict = Dict("n" => n, "start" => x_start, "sol" => x_sol,
 
 # ------------------------------------- Problem 23 -----------------------------------------
 @inbounds function p23_f!(out, x, p = nothing)
+    n = length(x)
     c = 0.9
-    out[1:n] = x[1:n]
-    μ = zeros(n)
-    for i in 1:n
-        μ[i] = (2 * i) / (2 * n)
+    @simd for i in 1:n
+        out[i] = x[i]
     end
     for i in 1:n
+        μi = i / n  # μ[i] = (2*i)/(2*n) = i/n
         s = 0.0
         for j in 1:n
-            s = s + (μ[i] * x[j]) / (μ[i] + μ[j])
+            μj = j / n
+            s = s + (μi * x[j]) / (μi + μj)
         end
         term = 1.0 - c * s / (2 * n)
         out[i] -= 1.0 / term
diff --git a/lib/NonlinearProblemLibrary/test/runtests.jl b/lib/NonlinearProblemLibrary/test/runtests.jl
index dbded51..9fe5dbc 100644
--- a/lib/NonlinearProblemLibrary/test/runtests.jl
+++ b/lib/NonlinearProblemLibrary/test/runtests.jl
@@ -1,8 +1,45 @@
 # The test is simply that all of the examples build!
 using NonlinearProblemLibrary
+using Test
 
 # Check that there are no undefined exports, stale dependencies, etc.
 # Ambiguity checks are disabled since tests fail due to ambiguities
 # in dependencies
 using Aqua
 Aqua.test_all(NonlinearProblemLibrary; ambiguities = false)
+
+# Allocation tests - ensure key functions don't allocate
+if get(ENV, "GROUP", "all") == "all" || get(ENV, "GROUP", "all") == "nopre"
+    @testset "Allocation Tests" begin
+        using AllocCheck
+
+        # Test p23_f! (Chandrasekhar function) - the fixed function
+        @testset "p23_f! zero allocations" begin
+            x = ones(10)
+            out = zeros(10)
+            # Warmup
+            NonlinearProblemLibrary.p23_f!(out, x)
+            # Test
+            allocs = @allocated NonlinearProblemLibrary.p23_f!(out, x)
+            @test allocs == 0
+        end
+
+        # Test other key functions
+        @testset "p1_f! zero allocations" begin
+            x = ones(10)
+            x[1] = -1.2
+            out = zeros(10)
+            NonlinearProblemLibrary.p1_f!(out, x)
+            allocs = @allocated NonlinearProblemLibrary.p1_f!(out, x)
+            @test allocs == 0
+        end
+
+        @testset "p2_f! zero allocations" begin
+            x = [3.0, -1.0, 0.0, 1.0]
+            out = zeros(4)
+            NonlinearProblemLibrary.p2_f!(out, x)
+            allocs = @allocated NonlinearProblemLibrary.p2_f!(out, x)
+            @test allocs == 0
+        end
+    end
+end