Machine Learning Foundations(NTU) 第一次作业

Machine Learning Foundations(NTU) 第一次作业

PLA

DATA: https://d396qusza40orc.cloudfront.net/ntumlone%2Fhw1%2Fhw1_15_train.dat

Each line of the data set contains one (xn,yn) with xn∈R4. T

he first 4 numbers of the line contains the components of xn orderly, the last number is yn.

Please initialize your algorithm with w=0 and take sign(0) as −1

Question 15:

Implement a version of PLA by visiting examples in the naive cycle using the

order of examples in the data set. Run the algorithm on the data set.

What is the number of updates before the algorithm halts?

Question 16:

Implement a version of PLA by visiting examples in fixed, pre-determined random

cycles throughout the algorithm. Run the algorithm on the data set. Please repeat

your experiment for 2000 times, each with a different random seed. What is the average

number of updates before the algorithm halts?

Question 17:

Implement a version of PLA by visiting examples in fixed, pre-determined random cycles

throughout the algorithm, while changing the update rule to be:

wt+1 = wt + alpha * yn(t)xn(t)

with alpha =0.5. Note that your PLA in the previous Question corresponds to alpha=1.

Please repeat your experiment for 2000 times, each with a different random seed.

What is the average number of updates before the algorithm halts?

[code]import urllib2
import numpy as np
import random

# url = 'https://d396qusza40orc.cloudfront.net/ntumlone%2Fhw1%2Fhw1_15_train.dat'
# f = urllib2.urlopen(url)
# with open("hw1_15_train.dat", "wb") as code:
#    code.write(f.read())

def train_PLA():
    code = open("hw1_15_train.dat", "r")
    lines = code.readlines()
    xn = np.zeros((len(lines), 5)).astype(np.float)
    yn = np.zeros((len(lines),)).astype(np.int)
    learn_rate = 0.5

    for i in range(0, len(lines)):
        line = lines[i]
        line = line.rstrip('\r\n').replace('\t', ' ').split(' ')
        xn[i, 0] = 1
        xn[i, 1] = float(line[0])
        xn[i, 2] = float(line[1])
        xn[i, 3] = float(line[2])
        xn[i, 4] = float(line[3])
        yn[i] = int(line[4])
        # print '---- ', i, ' --------',xn[i, 0], xn[i, 1], xn[i, 2], xn[i, 3], yn[i]

    wn = np.zeros((5, )).astype(np.float)

    updates = 1000
    cnt = 0
    for j in range(updates):
        is_stop = True
        idx = range(len(lines))
        idx = random.sample(idx, len(lines))
        for i in range(0, len(lines)):
            if int(np.sign(np.dot(wn, xn[idx[i]].transpose()))) != yn[idx[i]]:
                wn = wn + learn_rate * yn[idx[i]] * xn[idx[i]]
                is_stop = False
                cnt += 1
        if is_stop:
            break
    return cnt

updates = 0
for i in range(2000):
    updates = updates + train_PLA()
    print 'random :', i
print 'Average updates: ', updates / 2000.

Pocket PLA

Train DATA:

https://d396qusza40orc.cloudfront.net/ntumlone%2Fhw1%2Fhw1_18_train.dat

Test DATA: https://d396qusza40orc.cloudfront.net/ntumlone%2Fhw1%2Fhw1_18_test.dat

Question 18:

As the test set for “verifying” the g returned by your algorithm (see lecture 4 about verifying).

The sets are of the same format as the previous one.

Run the pocket algorithm with a total of 50 updates on D, and verify the performance of w using the test set.

Please repeat your experiment for 2000 times, each with a different random seed.

What is the average error rate on the test set?

Question 19:

Modify your algorithm in Question 18 to return w50 (the PLA vector after 50 updates) instead of

Wg (the pocket vector) after 50 updates. Run the modified algorithm on D, and verify the performance

using the test set. Please repeat your experiment for 2000 times, each with a different random seed.

What is the average error rate on the test set?

Question 20:

Modify your algorithm in Question 18 to run for 100 updates instead of 50, and verify the performance

of wPOCKET using the test set. Please repeat your experiment for 2000 times, each with a different random seed.

What is the average error rate on the test set?

[code]> __author__ = 'zgf'
import urllib2
import numpy as np
import random

url = 'https://d396qusza40orc.cloudfront.net/ntumlone%2Fhw1%2Fhw1_18_train.dat '
f = urllib2.urlopen(url)
with open("hw1_18_train.dat", "wb") as code:
   code.write(f.read())

def train_PLA():
    code = open("hw1_18_train.dat", "r")
    lines = code.readlines()
    xn = np.zeros((len(lines), 5)).astype(np.float)
    yn = np.zeros((len(lines),)).astype(np.int)
    learn_rate = 1

    for i in range(0, len(lines)):
        line = lines[i]
        line = line.rstrip('\r\n').replace('\t', ' ').split(' ')
        xn[i, 0] = 1
        xn[i, 1] = float(line[0])
        xn[i, 2] = float(line[1])
        xn[i, 3] = float(line[2])
        xn[i, 4] = float(line[3])
        yn[i] = int(line[4])

    wn = np.zeros((5, )).astype(np.float)
    wg = 0
    last_error = test_PLA(wn)
    updates = 100
    for i in range(0, updates):
        idx = range(len(lines))
        idx = random.sample(idx, len(lines))
        for i in idx:
            if int(np.sign(np.dot(wn, xn[idx[i]].transpose()))) != yn[i]:
                wn = wn + yn[i] * xn[i]
                new_error = test_PLA(wn)
                if last_error > new_error:
                    last_error = new_error
                    wg = wn
                break

    return updates, wg

def test_PLA(wn):
    code = open("hw1_18_test.dat", "r")
    lines = code.readlines()
    xn = np.zeros((len(lines), 5)).astype(np.float)
    yn = np.zeros((len(lines),)).astype(np.int)
    learn_rate = 1
    error_rate = 0

    for i in range(0, len(lines)):
        line = lines[i]
        line = line.rstrip('\r\n').replace('\t', ' ').split(' ')
        xn[i, 0] = 1
        xn[i, 1] = float(line[0])
        xn[i, 2] = float(line[1])
        xn[i, 3] = float(line[2])
        xn[i, 4] = float(line[3])
        yn[i] = int(line[4])
        # print '---- ', i, ' --------',xn[i, 0], xn[i, 1], xn[i, 2], xn[i, 3], yn[i]

    for i in range(0, len(lines)):
        y = int(np.sign(np.dot(wn, xn[i].transpose())))
        if y != yn[i]:
            error_rate += 1
    return error_rate * 1. / len(lines)

error_rate = 0
for i in range(2000):
    wg = train_PLA()[1]
    error = test_PLA(wg)
    error_rate += error
    print 'random :', i, '  error_rate: ', error
print 'Average error_rate: ', error_rate / 2000.