diff --git a/chapter05/log1pexp.m b/chapter05/log1pexp.m
deleted file mode 100644
index 7ad0b9d..0000000
--- a/chapter05/log1pexp.m
+++ /dev/null
@@ -1,7 +0,0 @@
-function y = log1pexp(x)
-% Accurately compute y = log(1+exp(x))
-% reference: Accurately Computing log(1-exp(|a|)) Martin Machler
-seed = 33.3;
-y = x;
-idx = x<seed;
-y(idx) = log1p(exp(x(idx)));
\ No newline at end of file
diff --git a/chapter05/sigmoid.m b/chapter05/sigmoid.m
deleted file mode 100644
index 9c82831..0000000
--- a/chapter05/sigmoid.m
+++ /dev/null
@@ -1,4 +0,0 @@
-function y = sigmoid(x)
-% Sigmod function
-% Written by Mo Chen (sth4nth@gmail.com).
-y = exp(-log1pexp(-x));
\ No newline at end of file
diff --git a/chapter08/mrfMaxSum.m b/chapter08/mrfMaxSum.m
new file mode 100644
index 0000000..084600c
--- /dev/null
+++ b/chapter08/mrfMaxSum.m
@@ -0,0 +1,6 @@
+function [ output_args ] = mrfMaxSum( input_args )
+% Max-sum loopy belief propagation on Markov random field 
+% Input:
+%   W: n x n sparse weight matrix of a graph
+% Written by Mo Chen (sth4nth@gmail.com).
+
diff --git a/chapter08/mrfSumProd.m b/chapter08/mrfSumProd.m
new file mode 100644
index 0000000..e0a706b
--- /dev/null
+++ b/chapter08/mrfSumProd.m
@@ -0,0 +1,8 @@
+function model = mrfSumProd(W)
+% Sum-product loopy belief propagation on Markov random field 
+% Input:
+%   W: n x n sparse weight matrix of a graph
+% Written by Mo Chen (sth4nth@gmail.com).
+
+
+