Tag Archives: 编程

Loops in Swift Code | 循环 Xúnhuán

Hello everybody! Today in class we have learned 👩‍🏫 how to write loops 循环 (Xúnhuán) in Swift code 👩‍💻. We learned two kinds of loops ➰.

The first type of loop that we learned was a loop ➿ that repeats itself for a certain amount of times⏲. We learned 🏫 how to write this kind of loop in Swift code. Here’s an example.

for i in 1 … 4 {
moveForward()
turnRight()
moveForward()
turnLeft()
}

for i in 1 ... 4 {
moveForward()
turnRight()
moveForward()
turnLeft()
}

Next we learned another loop ⭕ that repeats itself until the condition is false🙅‍♀️. This loop is called a while loop. Here’s an example.

while thereIsACoin {
moveForward()
collectCoin()
}

while thereIsACoin {
moveForward()
collectCoin()
}

In a while loop the loop will go forward ⏩ and collect the coin 💰 nonstop until the is no more coins ☹ in front of the coin collecter to collect. This is what we have accoplished today in class 👩‍🎓👨‍🎓.

We will learn much more very soon. Goodbye!!😃😃

In the meantime, please do your homework, and use the Swift documentation (aka “instructions”).

Learning Swift | 学习Swift

This weekend we started our first lesson on Swift. Swift is the language used by Apple across its products.

The class first tried using XCode, which is Apple’s IDE for Swift. But not every child is familiar with the Mac. So we switched to a learn Swift phone app, which worked well. But the class really love Swift Playground.  It is like Scratch to them.  The difference is that: we are going to make an app in two months using Swift.

The kids enjoyed programming a lot!  They didn’t want to stop.

The only minor issue is that it only works on iPads.

Ipython Shell Keyboard shortcuts 键盘快捷键 (Kuàijié jiàn)

In this past weekend’s coding class we practice keyboard ⌨ shortcuts in the interactive Python shell (Ipython).

Since most of the students are learning typing ⌨, practicing these keyboard shortcuts actually help them learn typing by reinforcing memory of where the keys are.

The keyboard shortcuts allows you to minimize finger movements on the keyboard, which means you don’t even have to lift your hand ✋ for the “Backspace”, ‘Home’, ‘End’ or arrow keys (most of the time).    Spend 15 minutes per day practicing these.  Pretty soon, you will be a fast coder.

🚕Navigation

keystroke Action
Ctrl-a Move cursor to the beginning of the line
Ctrl-e Move cursor to the end of the line
Ctrl-b or the left arrow key Move cursor back one character
Ctrl-f or the right arrow key Move cursor forward one character

👦Text Entry

Keystroke Action
Backspace key Delete previous character in line
Ctrl-d Delete next character in line
Ctrl-k Cut text from cursor to end of line
Ctrl-u Cut text from beginning of line to cursor
Ctrl-y Yank (i.e. paste) text that was previously cut
Ctrl-t Transpose (i.e., switch) previous two characters

🐞Command History

Keystroke Action
Ctrl-p (or the up arrow key) Access previous command in history
Ctrl-n (or the down arrow key) Access next command in history
Ctrl-r Reverse-search through command history

🐳Miscellaneous

Keystroke Action
Ctrl-l Clear terminal screen
Ctrl-c Interrupt current Python command
Ctrl-d Exit IPython session

The shortcuts are referenced from  Python Data Science Handbook.   As its author Jake Vanderplas says, these shortcuts are not inherent in Ipython shell itself, but are based on GNU Readline library.

Mobile payments | 移动支付

This weekend’s financial math class is all about payments, in particular, mobile payments and mobile wallet💰.

Mobile wallet 移动钱包 are digital forms of wallet that people carry (or used to carry) in their pockets.  As we do not tend to carry large amounts of money in wallets, mobile wallets are convenient for small payments (as opposed to payments in larger businesses).

📳 They hold digital information about payments including credit and/or debit card, bank account, pre-paid card, virtual currency information, coupons and loyalty membership, and wallet holder identifications.📟

A mobile wallet is a software application (app) 💻that does the following:

  • Secure enrollment of the holder (application download, identification)
  • Securely store user information such as phone number, email address, and mailing address

The flow chart below summarizes the history of technology and events that evolve over the last eighty years.

copyright (C) Magic Math Mandarin

In China and many places around the world 🌎, mobile payment is accounting for most of the retail payments.   So you should know about how it works.  Next class we will talk about the math that goes into making mobile payment secure.

Use snippets to code faster | snippet 加速编程

Today’s weekend programming lesson we covered how to save code snippets in a code editor, such as Sublime Test 3 (ST) and Visual Studio Code (code).

🙂 You can save these chunks of code so next time you wouldn’t have to type it again.

Until NeuralLink or other developments that can help us bypass typing all together, we want to find ways to save ourselves time from typing code.   Using snippet is a must for children, who may not be great at typing.   Here is how to do it in Sublime Test 3 (ST) and Visual Studio Code (code).

😎Sublime Test:
Tools – > Developer -> New Snippet.

😎VS Code:
Shift + Control + p

😎 Shift + Control + F: to search for a string in your folder (perhaps the name of the snippet you saved).

💡Write the snippet that can be used by the code editor:

Snippets are json files. Use this ➡ web app, or some packages, or write json if you prefer to put the code into the json format.

Explaining .json snippet in VS Code:

  • The first set of “” encloses the name of the snippet (call it anything you like).
  • Prefix defines a prefix used in the IntelliSense drop down. For example, if you have a snippet for plotting, you may want to prefix it with “plot”.
  • body is the snippet content.
  • Note that: $1, $2 for tab stops
  • Description is the description.  When you start typing the prefix of a snippet, its description will come up.

By the way, to quickly see what are the keyboard shortcuts are available in VS Code:

Ctrl + Shift + p

Our cofounder’s new book release

We are really proud of our co-founder(联合创始人 lián hé chuàng shǐ rén), Sarah Chen, for her new book release, which is now public.   Congratulations!

Her book is available in various outlets:

Here is her pre-release announcement on LinkedIn in July this year.

 

 

秋天好 | Autumn is good

Today in class we talked about autumn (qiū)(tiān) in this weekend’s Chinese lesson.

(qiū)(tiān)(dào)(qiū)(tiān)(hǎo)
(lán)(lán)(tiān)(kōng)白(bái)(yún)飘(piāo)
(bǎo)(bǎo)(tái)(tóu)(hā)(hā)(xiào)
magic math mandarin

Fall is here.  Fall is good.
Blue sky and white clouds.
The baby looks up and laughs.

Besides 中文, we are also working with other organizations to help children with computer programming 编程.

极客星晨少儿编程

Logit transform | 分数对数转换

After we discussed logarithm (‘log’) last week, we explored a bit on some commonly used methods that have log embedded in them.   For example, the logit function, or logit transform (using the “natural” logarithm).   We explained its definition by the following Python code.

>>> epsilon=0.001
>>> def logit(c):
>>>  d = np.log((c+epsilon)/(1+ epsilon-c))
>>>  return d

The following is the inverse, which is to bring what was transformed back to what it was before.

>>> def inverse_logit(a):
>>>  b = ((1+ epsilon)*np.exp(a) – epsilon)/(np.exp(a)+1)
>>>  return b

>> print(logit(0.1)) #-2.1883847407670785
>>> print(inverse_logit(logit(0.1))) #0.09999999999999999

It is much more revealing on what the logit transform is doing by looking at some pictures of how this works.  See how fast when it is transformed!   Why it is stretched instead of being shrunk?  We know that taking log is to do division multiple times (recall log10 of a number is how many times it needs to divide by 10 in order to become 1).     But when it applies to numbers between 0 and 1, it gives us the opposite effect.  A positive small number less than one has to divide by 10 negative times to become 1.  For example, 0.01 needs to be divided by 10 negative two times to be restored to 1.  That’s why you see that y axis we have negatives.

On the other hand, we also have positives in the y-axis.  That’s because about half of the numbers (c+epsilon)/(1+ epsilon-c) (the odds) are large positive numbers.  Play around with it and you will surely get it.

Magic Math Mandarin

>> x = np.linspace(0,1,1000)
>>> y = logit(x)
>>> plt.scatter(x=x, y=y, alpha=0.3)
>>> title =”logit transform”
>>> plt.title(“%s”%title)
>>> plt.xlabel(“numbers between 0 and 1 (inclusive”)
>>> plt.ylabel(“after logit transform”)
>>> plt.xlim(-6, 6)
>>> plt.ylim(-6, 6)
>>> plt.gca().set_aspect(‘equal’, adjustable=’box’)
>>> plt.draw()

Look at the same plot with the axis scaled differently:

Magic Math Mandarin

zero, one and two | 零,一,二

It is not easy for a young child to comprehend multiplication by 1, as how they are taught in school is often the robotic multiplication table.   She or he can very quickly answer mutiplications by 2, or 3.    Because of this, questions like “what is the product of 1,2, 3, 4” (i.e. 4 factorial) can get a wide range of answers because the number “1” confuses the young mind.

Pychologist says that an infant learns the number 2 before the number 1.   And we can see why: with 2, there is something to compare against, like two fingers.  If there is only one finger, there is no variation, it is confusing.

When we teach multiplication, don’t forget to show that math is an integral part of the real world around us.   It is invented to simplify addition.  Multiply by 1 means just the thing itself.  Multiply by 2 means adding two of this thing together.  Multiply by 3 means adding three of the thing together.  The thing can be a bag of candies or the footage of a home.

Finally, we should show children how to use computers (not calculators) to do computations.   While a question like “give me the sum from 1 to 199” can be solved within seconds with math tricks, a slightly different question “give me the product from 1 to 199” won’t work with the same trick.  But if you know how to make the computer do the job, you can still answer it within seconds.

 

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