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Preview LaTeX in Org Mode in MacOS

Using the right Emacs Version I failed to preview LaTeX with emacs-plus. If you have installed d12frosted/emacs-plus, uninstall it and use emacs-mac. brew tap railwaycat/emacsmacport brew install emacs-mac If you like the fancy spacemacs icon, install it with cask: brew cask install emacs-mac-spacemacs-icon Install Tex Download and install BasicTeX.pkg here. Add /Library/TeX/texbin to PATH. Install dvisvgm by sudo tlmgr update --self && sudo tlmgr install dvisvgm Emacs settings Add TeX related bin to path: (setenv "PATH" (concat (getenv "PATH") ":/Library/TeX/texbin")) Tell Org Mode to create svg images: (setq org-latex-create-formula-image-program 'dvisvgm) Now you can see the rendered LaTeX equation by calling org-preview-latex-fragment.

Using Dueling DQN to Play Flappy Bird

PyTorch provide a simple DQN implementation to solve the cartpole game. However, the code is incorrect, it diverges after training (It has been discussed here). The official code’s training data is below, it’s high score is about 50 and finally diverges. There are many reason that lead to divergence. First it use the difference of two frame as input in the tutorial, not only it loss the cart’s absolute information(This information is useful, as game will terminate if cart moves too far from centre), but also confused the agent when difference is the same but the state is varied.

Circular Import in Python

Recently, I found a really good example code for Python circular import, and I’d like to record it here. Here is the code: 1 2 3 4 5 6 7 8 # def X1(): return "x1" from Y import Y2 def X2(): return "x2" 1 2 3 4 5 6 7 8 # def Y1(): return "y1" from X import X1 def Y2(): return "y2" Guess what will happen if you run python X.

Python Dictionary Implementation

Overview CPython allocation memory to save dictionary, the initial table size is 8, entries are saved as <hash,key,value> in each slot(The slot content changed after Python 3.6). When a new key is added, python use i = hash(key) & mask where mask=table_size-1 to calculate which slot it should be placed. If the slot is occupied, CPython using a probing algorithm to find the empty slot to store new item.

TextCNN with PyTorch and Torchtext on Colab

PyTorch is a really powerful framework to build the machine learning models. Although some features is missing when compared with TensorFlow (For example, the early stop function, History to draw plot), its code style is more intuitive. Torchtext is a NLP package which is also made by =pytorch= team. It provide a way to read text, processing and iterate the texts. Google Colab is a Jupyter notebook environment host by Google, you can use free GPU and TPU to run your modal.

CSRF in Django

CSRF(Cross-site request forgery) is a way to generate fake user request to target website. For example, on a malicious website A, there is a button, click it will send request to When the user click this button, he will logout from website B unconsciously. Logout is not a big problem, but malicious website can generate more dangerous request like money transfer. Django CSRF protection Each web framework has different approach to do CSRF protection.

Create Node Benchmark in Py2neo

Recently, I’m working on a neo4j project. I use Py2neo to interact with graph db. Alghough Py2neo is a very pythonic and easy to use, its performance is really poor. Sometimes I have to manually write cypher statement by myself if I can’t bear with the slow excution. Here is a small script which I use to compare the performance of 4 diffrent ways to insert nodes. import time from graph_db import graph from py2neo.

Deploy Nikola Org Mode on Travis

Recently, I enjoy using Spacemacs, so I decided to switch to org file from Markdown for writing blog. After several attempts, I managed to let Travis convert org file to HTML. Here are the steps. Install Org Mode plugin First you need to install Org Mode plugin on your computer following the official guide: Nikola orgmode plugin. Edit conf.el Org Mode will convert to HTML to display on Nikola. Org Mode plugin will call Emacs to do this job.

Using Chinese Characters in Matplotlib

After searching from Google, here is easiest solution. This should also works on other languages: import matplotlib.pyplot as plt %matplotlib inline %config InlineBackend.figure_format = 'retina' import matplotlib.font_manager as fm f = "/System/Library/Fonts/PingFang.ttc" prop = fm.FontProperties(fname=f) plt.title("你好",fontproperties=prop) Output:


LSTM The avoid the problem of vanishing gradient and exploding gradient in vanilla RNN, LSTM was published, which can remember information for longer periods of time. Here is the structure of LSTM: The calculate procedure are: \[\begin{aligned} f_t&=\sigma(W_f\cdot[h_{t-1},x_t]+b_f)\\ i_t&=\sigma(W_i\cdot[h_{t-1},x_t]+b_i)\\ o_t&=\sigma(W_o\cdot[h_{t-1},x_t]+b_o)\\ \tilde{C_t}&=tanh(W_C\cdot[h_{t-1},x_t]+b_C)\\ C_t&=f_t\ast C_{t-1}+i_t\ast \tilde{C_t}\\ h_t&=o_t \ast tanh(C_t) \end{aligned}\] \(f_t\),\(i_t\),\(o_t\) are forget gate, input gate and output gate respectively. \(\tilde{C_t}\) is the new memory content. \(C_t\) is cell state.