# Antenna 天线

# Electromagnetic Radiation 电磁辐射

# Colored Pencils 彩铅

# Inception 盗梦空间

A thief who steals corporate secrets through the use of dream-sharing technology is given the inverse task of planting an idea into the mind of a C.E.O.

## Storyline

Dom Cobb is a skilled thief, the absolute best in the dangerous art of extraction, stealing valuable secrets from deep within the subconscious during the dream state, when the mind is at its most vulnerable. Cobb’s rare ability has made him a coveted player in this treacherous new world of corporate espionage, but it has also made him an international fugitive and cost him everything he has ever loved. Now Cobb is being offered a chance at redemption. One last job could give him his life back but only if he can accomplish the impossible, inception. Instead of the perfect heist, Cobb and his team of specialists have to pull off the reverse: their task is not to steal an idea, but to plant one. If they succeed, it could be the perfect crime. But no amount of careful planning or expertise can prepare the team for the dangerous enemy that seems to predict their every move. An enemy that only Cobb could have seen coming.

多姆·柯布 是一位经验老道的窃贼，他在这一行中算得上是最厉害的，因为他能够潜入人们精神最为脆弱的梦境中，窃取潜意识中有价值的秘密。柯布这一罕见的技能使他成为危险的企业间谍活动中最令人垂涎的对象，但这也让他成为了一名国际逃犯，失去自己的所爱。如今柯布有了一个赎罪的机会，只要完成最后一项任务他的生活就会回复本来面目。与以往不同的是，柯布和他的团队这一次的任务不是窃取思想，而是植入思想。如果他们成功，这就是一次完美犯罪。但是即使提前做好了细致专业的安排，也无法预料到危险的敌人对他们的行动早已了如指掌，而只有柯布能够预料到敌人的行踪。

# Nunchaku 双截棍

The Handcrafted **Nunchaku** or nunchucks (Japanese: ヌンチャク nunchaku, often “nunchuks“, “chainsticks“, “chuka sticks” or “karate sticks” in English) is a traditional Okinawan martial arts weapon consisting of two sticks connected at one end by a short chain or rope. The two sections of the weapon are commonly made out of wood, while the link is a cord or a metal chain. The nunchaku is most widely used in martial arts such as Okinawan kobudō and karate, and is used as a training weapon, since it allows the development of quicker hand movements and improves posture. Modern-day nunchaku can be made from metal, wood, plastic or fiberglass. Toy and replica versions made of polystyrene foam or plastic are also available. Possession of this weapon is illegal in some countries, except for use in professional martial art schools.

**双截棍**或双节棍（日语：ヌンチャク 英文中通常为“nunchuks”，“chainsticks”，“chuka sticks” 或 “karate sticks”）是一种传统的中国武术武器，短链或绳索连接有两根棍子。 武器的两部分通常由木头制成，而链节则是绳索或金属链。

**双截棍**在中国武术、冲绳kobudō和空手道等体育运动中得到广泛的使用，

并被用作训练武器，因为它可以加快手部动作并改善姿势。

现代双节棍可以由金属，木材，塑料或玻璃纤维制成。

也提供由聚苯乙烯泡沫或塑料制成的玩具和复制品版本。

在某些国家/地区拥有该武器是非法的，但在专业武术学校中除外。

# Pencil Sketch 素描

A pencil is an implement for writing or drawing, constructed of a narrow, solid pigment core in a protective casing that prevents the core from being broken or marking the user’s hand. Pencils create marks by physical abrasion, leaving a trail of solid core material that adheres to a sheet of paper or other surface. They are distinct from pens, which dispense liquid or gel ink onto the marked surface.

### Line art

A line drawing is the most direct means of expression. This type of drawing without shading or lightness, is usually the first to be attempted by an artist. It may be somewhat limited in effect, yet it conveys dimension, movement, structure and mood; it can also suggest texture to some extent.

### Shading

Line gives character but shading gives depth and value-it is like adding an extra dimension to the sketch.

# Oil Painting 油画

Oil painting is the process of painting with pigments with a medium of drying oil as the binder. Commonly used drying oils include linseed oil, poppy seed oil, walnut oil, and safflower oil. The choice of oil imparts a range of properties to the oil paint, such as the amount of yellowing or drying time. Certain differences, depending on the oil, are also visible in the sheen of the paints. An artist might use several different oils in the same painting depending on specific pigments and effects desired. The paints themselves also develop a particular consistency depending on the medium. The oil may be boiled with a resin, such as pine resin or frankincense, to create a varnish prized for its body and gloss.

# Fast Fourier Transform 快速傅立叶变换

The fast fourier transform or FFT is without exaggeration one of the most important algorithms created in the last century. So much of the modern technology that we have today such as wireless communication, GPS and in fact anything related to the vast field of signal processing relies on the insights of the FFT.

But it’s also one of the most beautiful albums you’ll ever see. The depth and sheer number of brilliant ideas that went into it is just astounding it’s easy to miss the beauty aspect of the FFT since it’s often introduced in fairly complex settings that require a lot of prerequisite knowledge such as the discrete fourier transform time domain to frequency domain conversions and much more.

The Fast Fourier Transform (FFT) is an efficient $O(N \log N)$ algorithm for calculating DFTs. The FFT exploits symmetries in the $W$ matrix to take a “divide and conquer” approach. We will first discuss deriving the actual FFT algorithm, some of its implications for the DFT, and a speed comparison to drive home the importance of this powerful algorithm.

To derive the FFT, we assume that the signal’s duration is a power of two: $N=2^l$ . Consider what happens to the even-numbered and odd-numbered elements of the sequence in the DFT calculation.

$$\begin{align}S(k) &=s(0)+s(2) e^{(-j) \frac{2 \pi 2 k}{N}}+\ldots+s(N-2) e^{(-j) \frac{2 \pi(N-2) k}{N}}+s(1) e^{(-j) \frac{2 \pi k}{N}}+s(3) e^{(-j) \frac{2 \pi \times (2+1) k}{N}}+\ldots+s(N-1) e^{(-j) \frac{2 \pi(N-2+1) k}{N}} \nonumber \ &=s(0)+s(2)e^{(-j)\frac{2\pi k}{\frac{N}{2}}} + \ldots + s(N-2)e^{(-j) \frac{2 \pi\left(\frac{N}{2}-1\right) k}{\frac{N}{2}}} +\left( s(1)+s(3) e^{(-j) \frac{2 \pi k}{\frac{N}{2}}}+\dots+s(N-1) e^{(-j) \frac{2 \pi\left(\frac{N}{2}-1\right) k}{\frac{N}{2}}}\right) e^{\frac{-(j 2 \pi k)}{N}} \end{align}$$

Each term in square brackets has the form of a $\frac{N}{2}$ -length DFT. The first one is a DFT of the even-numbered elements, and the second of the odd-numbered elements. The first DFT is combined with the second multiplied by the complex exponential $e^{\frac{-(j 2\pi k)}{N}}$. The half-length transforms are each evaluated at frequency indices $k \in{0, \ldots, N-1}$. Normally, the number of frequency indices in a DFT calculation range between zero and the transform length minus one. The computational advantage of the FFT comes from recognizing the periodic nature of the discrete Fourier transform. The FFT simply reuses the computations made in the half-length transforms and combines them through additions and the multiplication by $e^{\frac{-(j 2 \pi k)}{N}}$, which is not periodic over $\frac{N}{2}$, to rewrite the length-N DFT. The formula above illustrates this decomposition. As it stands, we now compute two length-$\frac{N}{2}$ transforms (complexity $2 O\left(\frac{N^{2}}{4}\right)$), multiply one of them by the complex exponential (complexity $O(N)$), and add the results (complexity $O(N)$). At this point, the total complexity is still dominated by the half-length DFT calculations, but the proportionality coefficient has been reduced.

Now for the fun. Because $N=2^l$, each of the half-length transforms can be reduced to two quarter-length transforms, each of these to two eighth-length ones, etc. This decomposition continues until we are left with length-2 transforms. This transform is quite simple, involving only additions. Thus, the first stage of the FFT has $\frac{N}{2}$length-2 transforms (see the bottom part of fomula). Pairs of these transforms are combined by adding one to the other multiplied by a complex exponential. Each pair requires 4 additions and 4 multiplications, giving a total number of computations equaling $8\frac{N}{4}=\frac{N}{2}$. This number of computations does not change from stage to stage. Because the number of stages, the number of times the length can be divided by two, equals $\log_2 N$, the complexity of the FFT is $O(N \log N)$.

The initial decomposition of a length-8 DFT into the terms using even- and odd-indexed inputs marks the first phase of developing the FFT algorithm. When these half-length transforms are successively decomposed, we are left with the diagram shown in the bottom panel that depicts the length-8 FFT computation.

法国数学家傅里叶提出，任何周期函数都可表示为不同频率的正弦函数和，

或余弦函数之和，其中每个正弦函数和，或余弦函数都要乘以不同的系数，这个和就称为傅里叶级数。

DFT 是指 Discrete Fourier Transform，离散傅里叶变换。

FFT 是指 快速傅里叶变换，它是 DFT 的一种简化计算。

它是根据离散傅氏变换的奇、偶、虚、实等特性，对离散傅立叶变换的算法进行改进获得的。

# Baduk 围棋入门 4.0

胡翼飞的围棋入门视频。

主要内容：一步棋的价值、收官的顺序、手动判定胜负、实战中的收官。

**收官**，又称作“官子”，是围棋比赛中三个阶段（布局、中盘、官子）中的最后一个阶段，

指双方经过中盘的战斗，地盘及死活已经大致确定之后，确立竞逐边界的阶段。

### 双方先手官子

无论谁下都是先手，则为双先官。因为谁先走谁无条件得利，所以双先官只要能走到就是最大的官子。

### 先手官和逆收官

一方走是先手，一方走是后手，先手的一方叫先手官，后手的一方叫逆收官。先手官和逆收官往往是同一个官子，大小也一样，只是称呼的对象不一样而已。先手和逆收官可以简单的理解为两倍后手官的价值。

### 后手官

无论谁下都是后手，即双方都是后手时，称为后手官。也可以理解为双方后手官的简称。当我们一般说官子的价值时，默认都是按后手官来理解的。例如说这个地方的官子是两目，指的就是双方后手两目。