diff --git a/regression/lecture/cubicerrors.py b/regression/lecture/cubicerrors.py
new file mode 100644
index 0000000..60a7bf8
--- /dev/null
+++ b/regression/lecture/cubicerrors.py
@@ -0,0 +1,102 @@
+import matplotlib.pyplot as plt
+import numpy as np
+
+def create_data():
+    # wikipedia:
+    # Generally, males vary in total length from 250 to 390 cm and
+    # weigh between 90 and 306 kg
+    c = 6
+    x = np.arange(2.2, 3.9, 0.05)
+    y = c * x**3.0
+    rng = np.random.RandomState(32281)
+    noise = rng.randn(len(x))*50
+    y += noise
+    return x, y, c
+
+    
+def plot_data(ax, x, y, c):
+    ax.scatter(x, y, marker='o', color='b', s=40, zorder=10)
+    xx = np.linspace(2.1, 3.9, 100)
+    ax.plot(xx, c*xx**3.0, color='#CC0000', lw=2, zorder=5)
+    for cc in [0.25*c, 0.5*c, 2.0*c, 4.0*c]:
+        ax.plot(xx, cc*xx**3.0, color='#FF9900', lw=1.5, zorder=5)
+    
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('Size x / m')
+    ax.set_ylabel('Weight y / kg')
+    ax.set_xlim(2, 4)
+    ax.set_ylim(0, 400)
+    ax.set_xticks(np.arange(2.0, 4.1, 0.5))
+    ax.set_yticks(np.arange(0, 401, 100))
+    
+    
+def plot_data_errors(ax, x, y, c):
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('Size x / m')
+    #ax.set_ylabel('Weight y / kg')
+    ax.set_xlim(2, 4)
+    ax.set_ylim(0, 400)
+    ax.set_xticks(np.arange(2.0, 4.1, 0.5))
+    ax.set_yticks(np.arange(0, 401, 100))
+    ax.set_yticklabels([])
+    ax.annotate('Error',
+                xy=(x[28]+0.05, y[28]+60), xycoords='data',
+                xytext=(3.4, 70), textcoords='data', ha='left',
+                arrowprops=dict(arrowstyle="->", relpos=(0.9,1.0),
+                connectionstyle="angle3,angleA=50,angleB=-30") )
+    ax.scatter(x[:40], y[:40], color='b', s=10, zorder=0)
+    inxs = [3, 10, 11, 17, 18, 21, 28, 30, 33]
+    ax.scatter(x[inxs], y[inxs], color='b', s=40, zorder=10)
+    xx = np.linspace(2.1, 3.9, 100)
+    ax.plot(xx, c*xx**3.0, color='#CC0000', lw=2)
+    for i in inxs :
+        xx = [x[i], x[i]]
+        yy = [c*x[i]**3.0, y[i]]
+        ax.plot(xx, yy, color='#FF9900', lw=2, zorder=5)
+
+def plot_error_hist(ax, x, y, c):
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('Squared error')
+    ax.set_ylabel('Frequency')
+    bins = np.arange(0.0, 1250.0, 100)
+    ax.set_xlim(bins[0], bins[-1])
+    #ax.set_ylim(0, 35)
+    ax.set_xticks(np.arange(bins[0], bins[-1], 200))
+    #ax.set_yticks(np.arange(0, 36, 10))
+    errors = (y-(c*x**3.0))**2.0
+    mls = np.mean(errors)
+    ax.annotate('Mean\nsquared\nerror',
+                xy=(mls, 0.5), xycoords='data',
+                xytext=(800, 3), textcoords='data', ha='left',
+                arrowprops=dict(arrowstyle="->", relpos=(0.0,0.2),
+                connectionstyle="angle3,angleA=10,angleB=90") )
+    ax.hist(errors, bins, color='#FF9900')
+
+
+
+if __name__ == "__main__":
+    x, y, c = create_data()
+    plt.xkcd()
+    fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(7., 2.6))
+    plot_data(ax1, x, y, c)
+    plot_data_errors(ax2, x, y, c)
+    #plot_error_hist(ax2, x, y, c)
+    fig.set_facecolor("white")
+    fig.tight_layout()
+    fig.savefig("cubicerrors.pdf")
+    plt.close()
diff --git a/regression/lecture/cubicfunc.py b/regression/lecture/cubicfunc.py
new file mode 100644
index 0000000..8ccc39e
--- /dev/null
+++ b/regression/lecture/cubicfunc.py
@@ -0,0 +1,40 @@
+import matplotlib.pyplot as plt
+import numpy as np
+
+if __name__ == "__main__":
+    # wikipedia:
+    # Generally, males vary in total length from 250 to 390 cm and
+    # weigh between 90 and 306 kg
+    c = 6
+    x = np.arange(2.2, 3.9, 0.05)
+    y = c * x**3.0
+    rng = np.random.RandomState(32281)
+    noise = rng.randn(len(x))*50
+    y += noise
+    
+    plt.xkcd()
+    fig, ax = plt.subplots(figsize=(7., 3.6))
+    
+    ax.scatter(x, y, marker='o', color='b', s=40, zorder=10)
+    xx = np.linspace(2.1, 3.9, 100)
+    ax.plot(xx, c*xx**3.0, color='#CC0000', lw=3, zorder=5)
+    for cc in [0.25*c, 0.5*c, 2.0*c, 4.0*c]:
+        ax.plot(xx, cc*xx**3.0, color='#FF9900', lw=2, zorder=5)
+    
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('Size x / m')
+    ax.set_ylabel('Weight y / kg')
+    ax.set_xlim(2, 4)
+    ax.set_ylim(0, 400)
+    ax.set_xticks(np.arange(2.0, 4.1, 0.5))
+    ax.set_yticks(np.arange(0, 401, 100))
+    
+    fig.set_facecolor("white")
+    fig.subplots_adjust(0.11, 0.16, 0.98, 0.97)
+    fig.savefig("cubicfunc.pdf")
+    plt.close()
diff --git a/regression/lecture/cubicmse.py b/regression/lecture/cubicmse.py
new file mode 100644
index 0000000..f1d3e5b
--- /dev/null
+++ b/regression/lecture/cubicmse.py
@@ -0,0 +1,93 @@
+import matplotlib.pyplot as plt
+import numpy as np
+
+def create_data():
+    # wikipedia:
+    # Generally, males vary in total length from 250 to 390 cm and
+    # weigh between 90 and 306 kg
+    c = 6
+    x = np.arange(2.2, 3.9, 0.05)
+    y = c * x**3.0
+    rng = np.random.RandomState(32281)
+    noise = rng.randn(len(x))*50
+    y += noise
+    return x, y, c
+
+def gradient_descent(x, y):
+    n = 20
+    dc = 0.01
+    eps = 0.0001
+    cc = 1.1
+    cs = []
+    mses = []
+    for k in range(n):
+        m0 = np.mean((y-(cc*x**3.0))**2.0)
+        m1 = np.mean((y-((cc+dc)*x**3.0))**2.0)
+        dmdc = (m1 - m0)/dc
+        cs.append(cc)
+        mses.append(m0)
+        cc -= eps*dmdc
+    return cs, mses
+    
+def plot_mse(ax, x, y, c, cs):
+    ms = np.zeros(len(cs))
+    for i, cc in enumerate(cs):
+        ms[i] = np.mean((y-(cc*x**3.0))**2.0)
+    ccs = np.linspace(0.5, 10.0, 200)
+    mses = np.zeros(len(ccs))
+    for i, cc in enumerate(ccs):
+        mses[i] = np.mean((y-(cc*x**3.0))**2.0)
+        
+    ax.plot(ccs, mses, 'b', lw=2, zorder=10)
+    ax.scatter(cs, ms, color='#cc0000', s=40, zorder=20)
+    ax.scatter(cs[-1], ms[-1], color='#FF9900', s=60, zorder=30)
+    for i in range(4):
+        ax.annotate('',
+                    xy=(cs[i+1]+0.2, ms[i+1]), xycoords='data',
+                    xytext=(cs[i]+0.3, ms[i]+200), textcoords='data', ha='left',
+                    arrowprops=dict(arrowstyle="->", relpos=(0.0,0.0),
+                    connectionstyle="angle3,angleA=10,angleB=70") )
+        
+    
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('c')
+    ax.set_ylabel('mean squared error')
+    ax.set_xlim(0, 10)
+    ax.set_ylim(0, 25000)
+    ax.set_xticks(np.arange(0.0, 10.1, 2.0))
+    ax.set_yticks(np.arange(0, 30001, 10000))
+    
+def plot_descent(ax, cs, mses):
+    ax.plot(np.arange(len(mses))+1, mses, '-o', c='#cc0000', mew=0, ms=8)
+    
+    ax.spines["right"].set_visible(False)
+    ax.spines["top"].set_visible(False)
+    ax.yaxis.set_ticks_position('left')
+    ax.xaxis.set_ticks_position('bottom')
+    ax.tick_params(direction="out", width=1.25)
+    ax.tick_params(direction="out", width=1.25)
+    ax.set_xlabel('iteration')
+    #ax.set_ylabel('mean squared error')
+    ax.set_xlim(0, 10.5)
+    ax.set_ylim(0, 25000)
+    ax.set_xticks(np.arange(0.0, 10.1, 2.0))
+    ax.set_yticks(np.arange(0, 30001, 10000))
+    ax.set_yticklabels([])
+
+
+if __name__ == "__main__":
+    x, y, c = create_data()
+    cs, mses = gradient_descent(x, y)
+    plt.xkcd()
+    fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(7., 2.6))
+    plot_mse(ax1, x, y, c, cs)
+    plot_descent(ax2, cs, mses)
+    fig.set_facecolor("white")
+    fig.tight_layout()
+    fig.savefig("cubicmse.pdf")
+    plt.close()
diff --git a/regression/lecture/regression-chapter.tex b/regression/lecture/regression-chapter.tex
index 60ceef7..792dfcd 100644
--- a/regression/lecture/regression-chapter.tex
+++ b/regression/lecture/regression-chapter.tex
@@ -25,13 +25,16 @@
 
 \subsection{Start with one-dimensional problem!}
 \begin{itemize}
-\item Let's fit a cubic function $y=cx^3$ (weight versus length of a tiger)
+\item Let's fit a cubic function $y=cx^3$ (weight versus length of a tiger)\\
+\includegraphics[width=0.8\textwidth]{cubicfunc}
 \item Introduce the problem, $c$ is density and form factor
 \item How to generate an artificial data set (refer to simulation chapter)
 \item How to plot a function (do not use the data x values!)
-\item Just the mean square error as a function of the factor c
+\item Just the mean square error as a function of the factor c\\
+\includegraphics[width=0.8\textwidth]{cubicerrors}
 \item Also mention the cost function for a straight line
-\item 1-d gradient, NO quiver plot (it is a nightmare to get this right)
+\item 1-d gradient, NO quiver plot (it is a nightmare to get this right)\\
+\includegraphics[width=0.8\textwidth]{cubicmse}
 \item 1-d gradient descend
 \item Describe in words the n-d problem.
 \item Homework is to do the 2d problem with the straight line!