随机应变 ABCD: Always Be Coding and … : хороший
storage class, data types
NULL, INTEGER, REAL, TEXT, BLOB
No booleans, use INTEGER instead
Ex:
false = 0
true = 1
attribute
Name TEXT
Price INTEGER
Style INTEGER
In Stock INTEGER
Description TEXT
CREATE TABLE headphones (_id INTEGER, name TEXT, price INTEGER, style INTEGER, in_stock INTEGER, description TEXT);
CREATE TABLE pets (_id INTEGER, name TEXT, bread TEXT, gender INTEGER, weight INTEGER);
Temporary Storage:Short term
-can be used for calculations or displaying data on screen
-quick to access
-short-lived
e.g.
-computer RAM
Permanent Storage:Long term
-can be used for storing user data
-slower to save and access data
-stick around forever(until deleted)
e.g.
-Hard disk, Flash drives
Different Data Storage Options
Files: good for saving large media files
SharedPreferences: Good for in-app user preferences, key and value, Unique String and primitive types and strings
SQLight Databases: Good for organizing a lot of related and structured data for easy access: Row, Column
commonly used for text data, easily grows in size and easily searchable
PS C:\Users\xxx> sqlite3 -version 3.15.0 2016-10-14 10:20:30 707875582fcba352b4906a595ad89198d84711d8 PS C:\Users\xxx> sqlite3 SQLite version 3.15.0 2016-10-14 10:20:30 Enter ".help" for usage hints. Connected to a transient in-memory database. Use ".open FILENAME" to reopen on a persistent database. sqlite> .open pets.db sqlite>
スマホのプッシュ通知
iOS:Apple Push Notification Service(APNs)
Android:Google Cloud Messaging(GCM)
①Apple / google よりデバイストークンを取得
②アプリ用サーバにデバイストークンを登録
(ユーザーIDや端末IDと紐づけて送信)
③デバイストークンとメッセージを送信
$ curl \
--header "Authorization:key=【APIキー】"\
--header "Content-Type:\"application/json\""\
https://android.googleapis.com/gcm/send\
-d"{\"registration_ids\":[\"【RegistrationID】\"],\"data\":
{\"message\":/"Hello monotty!\"}}"
iOSのプッシュ通知
Command, Frame data(Item, Item)
device_id, os, device_token
AndroidはテキストベースのシンプルなHTTP通信で送信できる
iOSは、ApnsPHPを使う
function connectAPSN($sslclient,$pem_path,$passphrase){
$ctx = stream_content_create();
stream_context_set_option($ctx, 'ssl', 'local_cert', $pem_path);
stream_context_set_option($ctx, 'ssl', 'passphrase', $passphrase);
$fp = stream_socket_client($sslclient, $err,
$errstr, 60, STREAM_CLIENT_CONNECT|STREAM_CLIENT_PERSISTENT, $ctx);
if (!$fp){
echo "接続エラーになったので1秒後再接続を試みます。メメタア!". PHP_EOL;
sleep(1);
$fp = connectAPSN($sslclient,$pem_path,$passphrase);
return $fp;
} else {
echo "APNS接続OK" . PHP_EOL;
return $fp;
}
// 送信処理
$passphrase = 'password';
$pem_path = '/xxx/xxx.pem';
$sslclient = 'ssl://gateway.sandbox.push.apple.com:2195';
$fp = connectAPSN($sslclient,$pem_path,$passphrase);
P^ = x/N
P^ = 100/1000 = 0.1
m = z*se
m = z * √p^(1-p^)/n
m = 0.019
z distribution μ=0, σ=1 -1.96, 1.96
N = 2000, x = 300
p^ = 300 / 2000
center of confident 0.15
Hypothesis Testing
P(results due to chance)
Pcont, Pexp
Pcont = Pexp
Pexp-Pcont = 0
Size vs. Power Trade-Off
How many page views
α = P(reject null | null true)
AB test is using data like user behavior to make a decision.
Which part of the future is better.
AB testing rather than useful for new experiment.
Overview
Example
Choose a metric
Review statistics
Design
Analyze
Examples of when to use A/B testing
・Movie recommendation site: new ranking algorithm
・Change backend-page load time, results users see etc.
・Test layout of initial page
probability
Repeated measurement of click-through-probability
visitors = 1000
unique clicks = 10
click-through-probability ≒10%
Binominal Distribution
@ p = 3/4
mean = P
std dev = √p(1-p)/N
P^ = 16/20 = 4/5
types of outcomes
independent events
identical distribution
T1 = 0.1/h(T2 – T1)
T2 = 0.1/h(T1 – T2)
Two types of friction
static: moves when F > μs・N
kinetic: F = μk * N
wheel slip
rolling, rocked
speed = 120 km/h
μ=1.0: 3.4s
μ=0.7: 4.9s
F = m*a
u*gravitational force(mg)
a = μ*g
t/ 120km/h = 1 / μg
t = 120km/h / μ*g
Computing the coefficient of Friction
s = 1 – w/v
F(s) = μ(s)*mqcG
V= -F(s)/mqc
F = ma
w = F(s)/mew – B
import math
from **** import *
h = 0.01
mass_quarter_car = 250.
mass_effective_wheel = 20.
g = 9.81
end_time = 5.
num_steps = int(end_time / h)
w = numpy.zeros(num_steps + 1)
v = numpy.zeros(num_steps + 1)
x = numpy.zeros(num_steps + 1)
times = h * numpy.array(range(num_steps + 1))
@show_plot(7, 7)
def plot_me():
axes_x = matplotlib.pyplot.subplot(411)
axes_v = matplotlib.pyplot.subplot(412)
axes_w = matplotlib.pyplot.subplot(413)
awes_s = matplotlib.pyplot.subplot(414)
def friction_coeff(slip):
return 1.1 * (1. - math.exp(-20. * slip)) - 0.4 * slip
def wheel_slip():
b_values = numpy.arange(70., 190.1, 30.)
for b in b_values:
x[0] = 0.
for step in range(num_steps):
if v[step] < 0.01:
break
s = max(0., 1. - w[step] / v[step])
w[step + 1] = max(0., w[step + 1])
axes_x.plot(times[:step], x[:step])
axes_v.plot(times[:step], v[:step])
axes_w.plot(times[:step], w[:step])
axes_s.plot(times[:step], 1. - w[:step] / v[:step])
p = int((0.35 + 0.4 * (b - b_values[0])/ (b_values[-1] - b_values[0])) * num_steps)
axes_x.annotate(b, (times[p], x[p]),
xytext = (-30, -30), textcoords = 'offset point',
arrowprops = dict(arrowstyle = '-', connectionstyle = 'arc3, '))
p = int((0.35 + 0.4 * (v - b_values[0]) / (b_values[-1] - b_values[0])) * num_steps)
axes_x.annotate(b, (times[p], x[p]),
xytext = (-30, -30), textcoords - 'offset points',
arrowprops = dict(arrowstyle = '-', connectionstyle = 'arc3, rad = 0.2', shrinkB = 0.))
return x, v, w
axes_x.set_ylabel('Position\nin m', multialignment = 'center')
axes_v.set_ylabel('Car velocity\nin m/s', multialignment = 'center')
axes_w.set_ylabel('Wheel velocity\nin m/s', multialignment = 'center')
axes_s.set_ylabel('Wheel\nslip', multialignment = 'center')
axes_s.set_xlabel('Time in s')
axes_s.set_ylim(0., 1.)
return wheel_slip()
x, v, w = plot_me()
y=2^x, y=3^x
the slope of the tangent line at x < 1, x > 1
the exponential function
y = e^x -> slope of the tange line is exactly 1.
e = lim n->∞(1 + 1/N)^N = 2.7
e^π = (1+ 3.1416/10,000)^10,000
(1 + x/4)^4 = 1 + x + 3/8x^2 + 1/16x^3 + 1/256x^4
e^x = 1 + x + x^2/2 + x^3/6 + x^4/24 + …
e^x+h = e^x * e^h
dy(x)/dx = -3y(x)
y(0) = 5
e = 2.71828 18284 59045 23536 02874 71352
Euler’s number & the exponential function
5^1 = 5, 5^0 = 1, 5^-2= 1/25, 5^1/2= √5, 5^3*5^4=5^7, (5^3)^4=5^12
x(t) = (x(t)^2 + 1)/2
with * (0) = 3
from *** import * end_time = 42. h = 0.0001 num_steps = int(end_time / h) times = h * numpy.array(range(num_steps) + 1) x = numpy.zeros(num_steps + 1) x[0] = 3. def forward_euler(): for step in range(num_steps): return x x = forward_euler() @show_plot def plot_me(): matplotlib.pyplot.plot(times, x) matplotlib.pyplot.show() plot_me()
Sources of Errors
-model, parameters, initial data, numerics