rec-4-12-2018

in life

Artificial Intelligence

Resolution

If $l_i \Leftrightarrow \neg m_j$, then:

$\frac{l_1 \vee \cdots l_k \ \ \ \ m_1 \vee \cdots \vee m_n}{l_1 \vee \cdots \vee l_{i-1} \vee l_{i+1} \cdots \vee l_k \vee m_1 \vee \cdots \vee m_{j-1} \vee m_{j+1} \cdots \vee m_n}$

If there is a empty clause after a resolution, it means there are conflicts.

$$ \frac{p\ \ \ \neg p}{\square} $$

Resolution algorithm to prove $\alpha$ within KB:

  1. Generate CNF of the knowledge base $KB\wedge\neg\alpha$
    • CNF: $(l_{1,1}\vee l_{1,2} \vee \cdots \vee l_{1,n_1}) \wedge (l_{2,1}\vee \cdots \vee l_{2,n_2})\vee\cdots \vee (l_{m,1}\vee\cdots\vee l_{m,n_m})$
    • Also called k-CNF if $n_1 = n_2 = \cdots = n_m = k$
  2. Repeat resolution process for every new rule
    1. If there is no new rule, $\alpha$ cannot be proved.
    2. If there is an empty literal, then stop and $\alpha$ is proved

Complexity: exponential

Expressiveness: better (not restricted to Horn clauses)

Propositional logic

Jargons

Use functions, predicates to represent relationships:

  • A is a person -> $Person(A)$, Person: predicate
  • Person a has a crippled left leg -> $Crippled(LeftLegOf(a))$, LeftLegOf: function (it’s OK since a human has only one left leg) Formally,

Term ::= Function ( Term {, Term}* ) AtomicSentence ::= predicate ( Term {, Term}* ) …

Model

Forgot that.

Networking

Cisco’s proprietary software, packettracer, couldn’t be downloaded without enrolling in its network course.

IOS

  • use enable to enable the thing
  • show interfaces to have a look at all interfaces, show interface [interface].
  • show vlan to show vlan
  • configure terminal to open the configuration in terminal
  • (config) interface [interface] to select an interface

Dynamic Trunking Protocol

A proprietary protocol invented by Cisco to negotiate trunking on a link between two VLAN-aware switches.

There is several modes for it:

  • access: puts the ethernet port into non-trunking mode and negotiates to convert the link to a nontrunk one, disregarding the neigboring port
  • trunk: puts the ethernet port into trunking mode and negotiates to convert the link to a trunk one, disregarding the neigboring port
  • dynamic auto: willing to trunk, will be trunk if the neighboring port is dynamic desirable or trunk
  • dynamic desirable: actively willing to trunk
  • nonegotiate: disable DTP. No wonder, it is not compatible with dynamic modes.

Except nonegotiate, all modes are triggered by (config-if) switchport mode [mode]. Switch to no-negotiate mode using (config-if) switchport nonegotiate.

Use a no before the statement to do the opposite thing, like:

(config-if) no shutdown: set up the link (config-if) no switchport nonegotiate: turn on DTP

Computer Graphics

Blurring is often used in computer graphics, like, to create HDR(high dynamic range) bloom, depth of field or other post process effects.

HDR bloom: since the real-world camera cannot focus perfectly, so it will convolve the incoming image with an Airy disk. What about the Airy disk? Know what a spot of light looks like in our eyes? That would be one. A perfect lens with a circular aperture would make it because the diffraction of light.

This effect is not noticeable when it is not so bright. However, with more light we can see the blurred edge of the bright part of the image, taken by a camera. And computer graphics tries to reproduce the same effect by blurring.

You can think up an approach instantly: take the average of neighboring blocks, like below:

$$ \begin{bmatrix} 1/9&1/9&1/9 \\ 1/9&1/9&1/9 \\ 1/9&1/9&1/9 \\ \end{bmatrix} $$ By all means this is bad. It will seem block-ish.

A better one is Gaussian blur. It uses the Gaussian distribution as the weight of neighboring pixels to calculate the average, or more accurately, do the convolution. The weight matrix, like the one above, is called kernel.

A 3x3 Gaussian kernel is like:

$$ \begin{bmatrix} 1/16 & 1/8 & 1/16 \\ 1/8 & 1/4 & 1/8 \\ 1/16 & 1/8 & 1/16 \\ \end{bmatrix} $$

Some other kernels are here.

It also can be used before downsampling: Gaussian blur gets rid of the sharp edges in the image, thus after downsampling, it will free the image from aliasing like moire patterns. Aliasing happens because of the poor sampling makes different signals indistinguishable, and some high frequency signals might get in the way after sampling. So a low pass filter need to be applied before sampling.

Task: sample => downscale image Reason of problem: high freq. signal => ? Problem: aliasing => moire pattern Solution: low pass filter => blurring

And yes, Gaussian blur is also a low pass filter, with a Bode plot like a parabola. Possibly it seems obvious at first sight: Gaussian distribution has a factor $e^{-\frac{x^2+y^2}{2\sigma^2}}$, which is stable through Fourier transforms.

We can calculate it out. Let’s put the basic calculus into practice. $$ \begin{aligned} &\iint e^{i\omega x}\cdot\frac{e^{-\frac{x^2+y^2}{2\sigma^2}}}{2\pi\sigma^2}\ dxdy\ =&e^{-2\sigma^2\omega^2}\iint \frac{e^{-\frac{(x-2\sigma^2\omega i)^2+y^2}{2\sigma^2}}}{2\pi\sigma^2}\ dxdy\ =&e^{-2\sigma^2\omega^2} \end{aligned} $$ So the amplification is: $$ \begin{aligned} dB&=20\log{e^{-2\sigma^2\omega^2}}\ &=-\frac{40}{\ln 10}\cdot \sigma^2\omega^2 \end{aligned} $$ Perfect! It is a parabola after all.

Leave Kawase to the next day.

Misc

マシンガンでも壊せなくて キャタピラーでも潰せなくて

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1984

Ignorance is strength.

高中买的书,终于在现在看完了。

我觉得这从一个侧面反映了在大学我的文化生活的严重缺失。

这就很糟糕。


这是在二战结束后不久的事。

世界分为三股力量:Eurasia, Eastasia 和Oceania。

三巨头之间爆发了核战争,这场战争使得生灵涂炭。在互相造成了巨大损失之后,达成和解。

一个反乌托邦的世界就开始了它的运转。

以上都是胡扯。都是编造出来的故事。

同意以上叙述的你的想法十分危险。可能需要跟我来Ministry of Love一趟。


看起来好像和发条橙很像,不过还是有点不同。

其实我就在这里胡说,反正在和Eastasia联手和Eurasia宣战的时候这篇文章会被修改或者删除的。

不用担心。

Big Brother包揽一切。

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NoirGif

A progamer.


Student(probably)