G52CPP

Lecture 1 & 2

Header

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#include <stdio.h> 	// C or C++
#include <cstdio> 	// C++

reference 省去 copy的过程
What is usually in a header file?

1. Function declarations
2. Macro definitions (#define)
3. Constant definitions
4. Possibly other things as well

   1. Ensure that the header file #includes everything that it needs itself
   2. Ensure that it doesn’t matter if the header file is #included multiple times
   3. Ensure that header files can be included in any order

   more >>

PyCharm运行TensorBoard时的小BUG

@(G53IDS)[PyCharm, TensorBoard, BUG]
今天在PyCharm的Terminal使用TensorBoard的时候出现了以下报错，但是mac自带的terminal却可以正常使用：

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# tensorboard --logdir=logs
Traceback (most recent call last):
  File "/Users/baron/.pyenv/versions/3.6.3/bin/tensorboard", line 11, in <module>
    sys.exit(main())
  File "/Users/baron/.pyenv/versions/3.6.3/lib/python3.6/site-packages/tensorboard/main.py", line 45, in main
    default.get_assets_zip_provider())
  File "/Users/baron/.pyenv/versions/3.6.3/lib/python3.6/site-packages/tensorboard/program.py", line 147, in main
    util.setup_logging()
  File "/Users/baron/.pyenv/versions/3.6.3/lib/python3.6/site-packages/tensorboard/util.py", line 50, in setup_logging
    locale.setlocale(locale.LC_ALL, '')
  File "/Users/baron/.pyenv/versions/3.6.3/lib/python3.6/locale.py", line 598, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

Hexo以及yilia主题个性化设置

修改浏览器Tab里的icon

修改后效果如下

• 很简单我们只需要在yilia主题里_config.yml文件里修改为favicon: /img/favicon.ico
• 将自己想要的icon，转换成.ico格式修改命名放在yilia/sourse/img里，大功告成

TensorFlow

配置环境

我的环境是 macOS Sierra 10.12.6，其他mac版本应该也适用。

pyenv

安装pyenv 管理多版本 python，通过它安装 python。原因是不希望污染mac自带系统python。详细过程参考官方doc，这里描述一下我的安装过程。

1. 安装：

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# 使用git安装
$ git clone https://github.com/pyenv/pyenv.git ~/.pyenv
# 使用Homebrew on Mac OS X 安装
$ brew update
$ brew install pyenv

没有Homebrew请安装并更新
more >>

Deadlocks

Overview

• Deadlocks and conditions for deadlocks
• Algorithms to detect[探知] deadlocks
  Approaches to recover from deadlocks more >>

N和NP问题

“P” refers to the class of problems that can be solved in polynomial time
“NP” refers to problems that can be solved in non- deterministic polynomial time

• P是能在多项式时间内解决的问题，
• NP是能在多项式时间验证答案正确与否的问题。

用大白话讲大概就是这样。P是否等于NP实质上就是在问，如果对于一个问题我能在多项式时间内验证其答案的正确性，那么我是否能在多项式时间内解决它？这个表述不太严谨，但通俗来讲就是如此。(2014, Wang)

什么是 polynomial time？

• 多项式级的复杂度：O(1),O(log(n)),O(n^a)等，因为它的规模n出现在底数的位置；
• 非多项式级的复杂度：O(a^n)和O(n!)型复杂度，其复杂度计算机往往不能承受。

Concurrency 2

Overview

• Software approaches: Peterson’s solution Hardware approaches:
• Disabling interrupts:
  • test_and_set()
  • compare_and_swap()
• Higher level approaches include mutexes and semaphores

  Peterson’s Solution

• Peterson’s solution is a software based solution which worked well for older machines
• Two shared variables are used:
  • turn: indicates which process is next to enter its critical section
  • boolean flag[2]: indicates that a process is ready to enter its critical section
• It is restricted[限制] to two processes that execute in strict alternation[严格的交替]

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  do { flag[j] = true; // j wants to enter critical section turn = i; // allow i to access first while (flag[i] && turn == i); // whilst i wants to access critical section // and its i’s turn, apply busy waiting // CRITICAL SECTION flag[j] = false; // remainder section } while (...);

Concurrency 1

Overview

• Examples of concurrency issues (e.g. counter++)
• Root causes of concurrency issues
• Critical sections and mutual exclusion
• Requirements and approaches for mutual exclusion

Concurrency

• Threads and processes execute concurrently or in parallel and can share resources
  • Multiprogramming/multiprocessing improves system utilisation
• A process/thread can be interrupted at any point in time (I/O, timer)
  • The process “state” is saved in the process control block
• The outcome of programs may become unpredictable[不可预知的]
  • Sharing data can lead to inconsistencies[矛盾]
  • I.e., the outcome of execution may depend on the order win which instructions are carried out