diff --git a/code/LDA/diagonalLDA.jl b/code/LDA/diagonalLDA.jl
index ef60c91b0e..6e44ea375e 100644
--- a/code/LDA/diagonalLDA.jl
+++ b/code/LDA/diagonalLDA.jl
@@ -45,6 +45,8 @@ function RegDiagLDA(X::Array{Float64, 2}, y::Array{Int, 1}, Δ::Float64)
     s0 = median(s) # typically choice
     # overall mean
     x_bar = mean(X, dims = 2)[:]
+    # count the number of genes
+    flag_genes = zeros(Bool, p, K)
     # for each class
     for k = 1:K
         # obs in class k
@@ -55,11 +57,14 @@ function RegDiagLDA(X::Array{Float64, 2}, y::Array{Int, 1}, Δ::Float64)
         mk = sqrt( 1 / sum(y.==k) - 1 / N )
         dk = ( xk_bar - x_bar ) ./ (mk * (s .+ s0))
         dk_prime = soft_threshold(dk, Δ)
+        flag_genes[:, k] .= dk_prime .!= 0
         xk_bar_prime = x_bar + mk*(s .+ s0) .* dk_prime
         # discriminant function
         push!(δ, x-> -sum( ( (x-xk_bar_prime)./s ).^2 )  ) # equal π_k
     end
-    return δ
+    # number of genes
+    num_genes = sum(any(flag_genes, dims = 2))
+    return δ, num_genes
 end
 
 function soft_threshold(x::Float64, Δ::Float64)
@@ -86,17 +91,52 @@ function  classify(x::Array{Float64, 2}, δ::Array{Function, 1})
     return res
 end
 
+# misclassification error
+function calc_err(pred::Array{Int, 1}, truth::Array{Int, 1})
+    return sum(pred .!= truth) / length(pred)
+end
+
+# cross validation
+function cv_err(X::Array{Float64, 2}, y::Array{Int, 1}, Δ; nfold = 10)
+    N = size(X, 2)
+    folds = div_into_folds(N, K = nfold)
+    err = zeros(nfold)
+    for k = 1:nfold
+        test_idx = folds[k]
+        train_idx = setdiff(1:N, test_idx)
+        δ, ng = RegDiagLDA(X[:, train_idx], y[train_idx], Δ)
+        err[k] = calc_err(classify(X[:, test_idx], δ), y[test_idx]) * length(test_idx)
+    end
+    return sum(err) / N
+end
+
+# 1:N divide into K-fold
+function div_into_folds(N::Int; K::Int = 10)
+    # maximum quota per fold
+    n = Int(ceil(N/K))
+    # number folds for the maximum quota
+    k = N - (n-1)*K
+    # number fols for n-1 quota: K-k
+    folds = Array{Array{Int, 1}, 1}(undef, K)
+    for i = 1:k
+        folds[i] = collect(n*(i-1)+1:n*i)
+    end
+    for i = 1:K-k
+        folds[k+i] = collect((n-1)*(i-1)+1:(n-1)*i) .+ n*k
+    end
+    return folds
+end
 
 # read data
 path = "data\\SRBCT\\" # windows style
 xtrain = readdlm(path*"khan.xtrain.txt")
-ytrain = readdlm(path*"khan.ytrain.txt", Int)
+ytrain = vec(readdlm(path*"khan.ytrain.txt", Int))
 xtest = readdlm(path*"khan.xtest.txt")
 ytest = readdlm(path*"khan.ytest.txt")
 
 # remove NA obs
 idx_nonNA = ytest .!= "NA"
-ytest = ytest[idx_nonNA]
+ytest = convert(Array{Int, 1}, ytest[idx_nonNA])
 xtest = xtest[:, vec(idx_nonNA)]
 
 # run
@@ -114,7 +154,7 @@ freqtable(cltest, ytest[1,:])
 
 
 # RegDiagLDA
-δ2 = RegDiagLDA(xtrain, ytrain[:], 2.0)
+δ2, ng = RegDiagLDA(xtrain, ytrain[:], 2.0)
 cl2 = classify(xtrain, δ2)
 cltest2 = classify(xtest, δ2)
 freqtable(cl2, ytrain[:])
@@ -124,5 +164,43 @@ freqtable(cl2, ytrain[:])
 
 
 
-
 freqtable(cltest2, ytest[:])
+# misclassification error
+calc_err(cltest2, ytest[:])
+
+# Error curves (fig 18.4 top)
+Δs = 0:0.2:8
+errs = zeros(length(Δs), 3) # traing, 10-fold, test
+ngs = zeros(Int, length(Δs))
+for i = 1:length(Δs)
+    δ, ngs[i] = RegDiagLDA(xtrain, ytrain, Δs[i])
+    # train error
+    errs[i, 1] = calc_err(classify(xtrain, δ), ytrain)
+    # cv10
+    errs[i, 2] = cv_err(xtrain, ytrain, Δs[i])
+    # test errror
+    errs[i, 3] = calc_err(classify(xtest, δ), ytest)
+end
+
+using Plots
+plot(Δs, errs[:, 1], label="Training", color = "green", legend=:topleft)
+scatter!(Δs, errs[:, 1], color = "green", label="")
+plot!(Δs, errs[:, 2], label="10-fold CV", color = "orange")
+scatter!(Δs, errs[:, 2], color = "orange", label="")
+plot!(Δs, errs[:, 3], label="Test", color = "blue")
+scatter!(Δs, errs[:, 3], color = "blue", label="")
+
+using PyPlot
+fig, ax1 = plt.subplots(figsize=(12, 8))
+ax1.plot(Δs, errs[:,1], label="Training", color="green", marker="o")
+ax1.plot(Δs, errs[:,2], label="10-fold CV", color = "orange", marker = "o")
+ax1.plot(Δs, errs[:,3], label="Test", color = "blue", marker = "o")
+ax1.legend(loc = "upper left")
+ax1.set_xlabel("Amount of Shrinkage Δ")
+ax1.set_ylabel("Misclassification Error")
+ax2 = ax1.twiny()
+ax2.set_xticks(Δs[1:5:end])
+ax2.set_xticklabels(ngs[1:5:end])
+ax2.set_xlabel("Number of Genes")
+plt.savefig("error_curves.png")
+plt.show()
diff --git a/code/LDA/error_curves.png b/code/LDA/error_curves.png
new file mode 100644
index 0000000000..8f04816170
Binary files /dev/null and b/code/LDA/error_curves.png differ