Math599 2023S

$\newcommand{\trans}{^\top} \newcommand{\adj}{^{\rm adj}} \newcommand{\cof}{^{\rm cof}} \newcommand{\inp}[2]{\left\langle#1,#2\right\rangle} \newcommand{\dunion}{\mathbin{\dot\cup}} \newcommand{\bzero}{\mathbf{0}} \newcommand{\bone}{\mathbf{1}} \newcommand{\ba}{\mathbf{a}} \newcommand{\bb}{\mathbf{b}} \newcommand{\bc}{\mathbf{c}} \newcommand{\bd}{\mathbf{d}} \newcommand{\be}{\mathbf{e}} \newcommand{\bh}{\mathbf{h}} \newcommand{\bp}{\mathbf{p}} \newcommand{\bq}{\mathbf{q}} \newcommand{\br}{\mathbf{r}} \newcommand{\bx}{\mathbf{x}} \newcommand{\by}{\mathbf{y}} \newcommand{\bz}{\mathbf{z}} \newcommand{\bu}{\mathbf{u}} \newcommand{\bv}{\mathbf{v}} \newcommand{\bw}{\mathbf{w}} \newcommand{\tr}{\operatorname{tr}} \newcommand{\nul}{\operatorname{null}} \newcommand{\rank}{\operatorname{rank}} %\newcommand{\ker}{\operatorname{ker}} \newcommand{\range}{\operatorname{range}} \newcommand{\Col}{\operatorname{Col}} \newcommand{\Row}{\operatorname{Row}} \newcommand{\spec}{\operatorname{spec}} \newcommand{\vspan}{\operatorname{span}} \newcommand{\Vol}{\operatorname{Vol}} \newcommand{\sgn}{\operatorname{sgn}} \newcommand{\idmap}{\operatorname{id}} \newcommand{\am}{\operatorname{am}} \newcommand{\gm}{\operatorname{gm}} \newcommand{\mult}{\operatorname{mult}} \newcommand{\iner}{\operatorname{iner}}$

$\newcommand{\january}{\text{principal component analysis}} \newcommand{\february}{\text{multidimensional scaling}} \newcommand{\march}{k\text{-means clustering}} \newcommand{\april}{\text{DBSCAN}} \newcommand{\may}{\text{linear regression}} \newcommand{\june}{\text{polynomial regression}} \newcommand{\july}{k\text{-nearest neighbors classification}} \newcommand{\august}{\text{decision tree classification}} \newcommand{\mother}[5]{#1\cdot#5} \newcommand{\energy}{\sum_{i=0}^{N-1}(y_i - c_0 - c_1x_i)^2} \newcommand{\potential}{\sum_{i=0}^{N-1}(y_i - c_0x_i - c_1e^{x_i})^2} \newcommand{\derivative}{\text{principal component}} \newcommand{\innerproduct}{\text{explained variance}} \newcommand{\singularities}{\text{centers}} \newcommand{\eigenvalues}{\text{cores}}$

ML exam

Please find the ipynb and related files for this exam through the link below.
https://hackmd.io/@jephianlin/H1fVKl1Uh

Name:

Student ID #:

Please read the instructions carefully:

1. Write your name and Student ID # first.
2. Write down your answers on the exam paper; no need to write down the code.
3. You are allowed to use the internet, but you are NOT allowed to communicate with others in any form.
4. Do NOT use your cell phone, use the computer instead.
5. Different problems might use same variable names. Make sure you use the right one to answer the problem.
6. If the answer is too long, write two digits after the decimal point.

---

Load the packages

import numpy as np
import matplotlib.pyplot as plt
np.set_printoptions(precision=3, suppress=True)

Download the dataset

Please do not modify the files.

import os
import urllib
import numpy as np

base = r"https://github.com/SageLabTW/auto-grading/raw/master/nsysu-digits/"
for c in ['X', 'y']:
    filename = "nsysu-digits-%s.csv"%c
    if filename not in os.listdir('.'):
        print(filename, 'not found --- will download')
        urllib.request.urlretrieve(base + c + ".csv", filename)

Problem 1 [2pt]

Let

A = np.array([[1,1,1,1],
              [2,2,2,2],
              [3,3,3,3]])
grid = np.meshgrid(np.arange(3), 
                   np.arange(3), 
                   np.arange(3))
xx = grid[0].ravel()
yy = grid[1].ravel()
zz = grid[2].ravel()
C = np.vstack([xx, yy, zz]).T

Apply $\january$ to $X = \mother{C}{1}{2}{3}{A}$ and find its first $\derivative$ (index 0 ).

Your answer:

A = np.array([[1,1,1,1],
              [2,2,2,2],
              [3,3,3,3]])
grid = np.meshgrid(np.arange(3), 
                   np.arange(3), 
                   np.arange(3))
xx = grid[0].ravel()
yy = grid[1].ravel()
zz = grid[2].ravel()
C = np.vstack([xx, yy, zz]).T
X = C.dot(A)

from sklearn.decomposition import PCA
model = PCA(1)
X_new = model.fit_transform(X)
model.components_

array([[0.5, 0.5, 0.5, 0.5]])

Problem 2 [2pt]

Let

A = np.array([[1,1,1,1],
              [2,2,2,2],
              [3,3,3,3]])
grid = np.meshgrid(np.arange(3), 
                   np.arange(3), 
                   np.arange(3))
xx = grid[0].ravel()
yy = grid[1].ravel()
zz = grid[2].ravel()
C = np.vstack([xx, yy, zz]).T

Apply the $\january$ to $X = \mother{C}{1}{2}{3}{A}$. Then use the $\innerproduct$ to determine the dimension of the data.

Your answer:

A = np.array([[1,1,1,1],
              [2,2,2,2],
              [3,3,3,3]])
grid = np.meshgrid(np.arange(3), 
                   np.arange(3), 
                   np.arange(3))
xx = grid[0].ravel()
yy = grid[1].ravel()
zz = grid[2].ravel()
C = np.vstack([xx, yy, zz]).T
X = C.dot(A)

from sklearn.decomposition import PCA
model = PCA(4)
X_new = model.fit_transform(X)
plt.plot(np.arange(1,5), model.explained_variance_ratio_.cumsum())
print("1 dimension is enough to get almost 100% explained variance.")

1 dimension is enough to get almost 100% explained variance.

Problem 3 [2pt]

Suppose at some step of the $\march$, we get three $\singularities$

$$ \begin{aligned} \mu_0 &= (1,1,1,1), \\ \mu_1 &= (2,2,2,2), \\ \mu_2 &= (3,3,3,3). \end{aligned} $$

Following the $\march$, how should we label the point $\bp = (2,2,2,1)$?

Your answer:

mus = np.array([[1,1,1,1],
                [2,2,2,2],
                [3,3,3,3]])
p = np.array([2,2,2,1])

dist = np.linalg.norm(mus - p, axis=1)
dist.argmin()

1

Problem 4 [2pt]

Let

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
X = Xsys[ysys==0]

Apply $\april$ to X and find out the number of $\eigenvalues$.

Your answer:

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
X = Xsys[ysys==0]

from sklearn.cluster import DBSCAN
model = DBSCAN(eps=1100, min_samples=5)
model.fit(X)

# The problem did not provide you with 
# the hyperparameters eps and min_samples,
# so any answer is correct.  
# Everyone will receive 2 points for this problem.
model.core_sample_indices_.shape

(143,)

Problem 5 [2pt]

Let

x = np.arange(1,11)
y = 0.5 * x + 3 + 0.5*np.sin(x)

Let $x_0, \ldots, x_{N-1}$ and $y_0, \ldots, y_{N-1}$ be the entries of x and y , respectively. Find $c_0$ and $c_1$ such that $\energy$ is minimized.

Your answer:

x = np.arange(1,11)
y = 0.5 * x + 3 + 0.5*np.sin(x)
X = x[:,np.newaxis]

from sklearn.linear_model import LinearRegression
model = LinearRegression()
model.fit(X, y)
y_new = model.predict(X)
plt.plot(x, y_new, c='red')
plt.scatter(x, y)

print('c0 =', model.intercept_)
print('c1 =', *model.coef_)

c0 = 3.183686321910917
c1 = 0.47943147211817894

Problem 6 [2pt]

Let

x = np.linspace(-1.5,0,10)
y = np.sin(x)

Let $x_0, \ldots, x_{N-1}$ and $y_0, \ldots, y_{N-1}$ be the entries of x and y , respectively. Find $c_0$ and $c_1$ such that $\potential$ is minimized.

Your answer:

x = np.linspace(-1.5,0,10)
y = np.sin(x)
X = np.vstack([x, np.exp(x)]).T

from sklearn.linear_model import LinearRegression
model = LinearRegression(fit_intercept=False)
model.fit(X, y)
y_new = model.predict(X)
plt.plot(x, y_new, c='red')
plt.scatter(x, y)

print('c0, c1 =', model.coef_)

c0, c1 = [ 0.741 -0.089]

Problem 7 [2pt]

Let

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
mask = (ysys==0) | (ysys==1)
X = Xsys[mask]
y = ysys[mask]

Apply $\july$ to X and y with n_neighbors=5 . Read the image
https://github.com/SageLabTW/auto-grading/blob/master/sampleJ/sampleJ_000.png
by downloading it and

from PIL import Image
img = Image.open('sampleJ_000.png')
img = np.array(img)

What is the prediction of it according to your model?

Your answer:

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
mask = (ysys==0) | (ysys==1)
X = Xsys[mask]
y = ysys[mask]

from sklearn.neighbors import KNeighborsClassifier
model = KNeighborsClassifier(5)
model.fit(X, y)

from PIL import Image
img = Image.open('sampleJ_000.png')
img = np.array(img)

X_new = img.reshape(1,784)
y_new = model.predict(X_new)
y_new

/home/jephian/.local/lib/python3.10/site-packages/sklearn/neighbors/_classification.py:228: FutureWarning: Unlike other reduction functions (e.g. `skew`, `kurtosis`), the default behavior of `mode` typically preserves the axis it acts along. In SciPy 1.11.0, this behavior will change: the default value of `keepdims` will become False, the `axis` over which the statistic is taken will be eliminated, and the value None will no longer be accepted. Set `keepdims` to True or False to avoid this warning.
  mode, _ = stats.mode(_y[neigh_ind, k], axis=1)

array([0])

Problem 8 [2pt]

Let

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
mask = (ysys==0) | (ysys==1)
X = Xsys[mask]
y = ysys[mask]

Read the image
https://github.com/SageLabTW/auto-grading/blob/master/sampleJ/sampleJ_000.png
by downloading it and

from PIL import Image
img = Image.open('sampleJ_000.png')
img = np.array(img)

What are the votes from its $5$ nearest neighbors?

Your answer:

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
mask = (ysys==0) | (ysys==1)
X = Xsys[mask]
y = ysys[mask]

from PIL import Image
img = Image.open('sampleJ_000.png')
img = np.array(img)

X_new = img.reshape(1,784)
dist = np.linalg.norm(X - X_new, axis=1)
nbrs = np.argpartition(dist, 4)[:5]
votes = y[nbrs]
print(votes)

[0 0 0 0 0]

Problem 9 [2pt]

Consider the tree

Which node does the data point $\bp = (1,-2)$ belong to?
(Left means True, while Right means False.)

Your answer:

print("Node #6")

Node #6

Problem 10 [2pt]

Base on the information

tree.children_left  = [1, 3, 5, -1, 7, -1, -1, -1, -1]
tree.children_right = [2, 4, 6, -1, 8, -1, -1, -1, -1]

draw the tree.

Your answer:

     0
    / \
  1     2
 / \   / \
3   4 5   6
   / \
  7   8

Problem 11 [extra 2pt]

Let

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
X = Xsys[:1300]
y = ysys[:1300]
X_test = Xsys[1300:]
y_test = ysys[1300:]

The dataset Xsys contains 1639 flattened images. Train a model (of your choice) with X anad y . Then test your model with X_test and y_test . How good is the accuracy you can get?

Write a few sentences describing how you train your model and tell me its accuracy. (open answer)

Please keep your code somewhere. If your model has a very good performance, I would love to learn more about your work.

Your answer:

Any classification model is okay

Xsys = np.genfromtxt('nsysu-digits-X.csv', dtype=int, delimiter=',') ### flattened already
ysys = np.genfromtxt('nsysu-digits-y.csv', dtype=int, delimiter=',')
X = Xsys[:1300]
y = ysys[:1300]
X_test = Xsys[1300:]
y_test = ysys[1300:]

from sklearn.tree import DecisionTreeClassifier
model = DecisionTreeClassifier()
model.fit(X, y)
y_model = model.predict(X_test)

from sklearn.metrics import accuracy_score
accuracy_score(y_test, y_model)

0.35988200589970504

---

Exam ends here.
Total point = 20 (+2)

Your score: