'분류 전체보기'에 해당되는 글 93건

A (1, 1)
B (1, 0)

1. A outer product B
| 1 0 |
| 1 0 |

2. |A cross product B| => determinant
|ab -bc| => |1 * 0 - 1 * 1| = |-1|

보통 흔히 말하는 A와 B가 이루는 면적은 cross product의 크기가 된다. outer product와는 관련이 없다.
그리고 A,B 가 이루는 면은 삼각형이 아니라 평행 사변형이다.

참고로, cross product는 determianat 계산법으로 계산이 된다.
https://en.wikipedia.org/wiki/Cross_producthttps://en.wikipedia.org/wiki/Determinant

| i  j  k|
| a b c|
| d e f| 로 두고, determinant를 구하면 i(bf - ce) - j(af - cd) + k(ae-bd) 가 되고 각각의 괄호안에 있는 값이 바로 i, j, k가 된다.

det를 구하는 방법의 원리는 아래 링크에서 라플라스 전개를 보면 이해가 쉽다.
https://ko.wikipedia.org/wiki/%ED%96%89%EB%A0%AC%EC%8B%9D

https://docs.ejabberd.im/admin/configuration/

find  "ACL Definition"

1. If you didn't open required ports,
    please check https://stackoverflow.com/questions/36862874/erlang-ejabberd-join-cluster-error-no-ping
    FIREWALL_WINDOW=4200-4210  in ejabberdctl.cfg setting is mandatory.

2. You already opened all required ports, but you are getting no_ping error,
    set hosts config. /etc/hosts -> add your ejabbered node hostname. (in my case, node1, node2)

ex)
...
node1    10.0.100.1
node2    10.0.100.2

How to set ejabberd cluster. step by setp

1. ejabberd.yml -> use same file config
2. ejabberdctl.cfg ->
  use same all but
  ERLANG_NODE=ejabberd@each-node-hostname
  FIREWALL_WINDOW=4200-4210

3. add node1, node2 on /etc/hosts
4. node1) ejabberdctl start
5. node2) ejabberdctl start
6. node2) ejabberdctl --no-timeout join_cluster 'ejabberd@node1'

It can be difficultly installed with https://github.com/processone/ejabberd-contrib/tree/master/mod_pottymouth

Instructions

mkdir -p $EJABBERD_HOME/erlang-lib/bitarray
cd $EJABBERD_HOME/erlang-lib/bitarray
clone https://github.com/ferd/bitarray git repo
run: /usr/lib/erlang/bin/escript rebar get-deps
run: /usr/lib/erlang/bin/escript rebar compile
run: /usr/bin/install -c -d /usr/local/lib/bitarray-1.0.0/ebin
run: /usr/bin/install -c -d /usr/local/lib/bitarray-1.0.0/priv
run: /usr/bin/install -c -m 644 ./ebin/bitarray.app /usr/local/lib/bitarray-1.0.0/ebin/bitarray.app
run: /usr/bin/install -c -m 644 ./ebin/bitarray.beam /usr/local/lib/bitarray-1.0.0/ebin/bitarray.beam 
run: /usr/bin/install -c -m 644 ./priv/bitarray.so /usr/local/lib/bitarray-1.0.0/priv/bitarray.so

What is $EJABBERD_HOME? default may be ~/ folder.
So, export EJABBERD_HOME=/user/yourhome
in bittarray/rebar.conf, change proper version 1.0 -> 1.2

And Let's get mod_pottymouth

mkdir -n ~/.ejabberd-modules/sources
cd ~/.ejabberd-modules/sources
git clone https://github.com/processone/ejabberd-contrib.git
cd mod_pottymouth

make sure ejabberd is running
run: ejabberdctl module_install mod_pottymouth
run: ejabberdctl restart
module will be installed in: ~/.ejabberd-modules/mod_pottymouth

May be you cannot module_install mod_pottymouth

1. remove -include("ejabberd.hrl"). line of mod_pottymouth.erl

2. add this. end of mod_pottymouth.erl

mod_options(_) -> [{blacklists, []}, {charmaps, []}].

3. add this. end of mod_pottymouth.erl -export([ here]) 

mod_options/1

After this module_install mod_pottymouth will be work.

I created pull request about this. 
https://github.com/processone/ejabberd-contrib/pull/253

고루틴의 CS 시점

시스템 콜이 발생하면 고루틴의 CS가 이루어진다는 것을 알았습니다. 그러면 정확히 어느 시점에서 고루틴의 CS가 이루어질까요? 고루틴의 CS는 다음 시점에서 이루어집니다:

• unbuffered 채널에 접근할 때(읽거나 쓸 때)
• 시스템 I/O가 발생했을 때
• 메모리가 할당되었을 때
• time.Sleep() 코드 실행(python asyncio에서 asyncio.sleep()을 이용해 yield하는 것과 유사합니다)
• runtime.Gosched() 코드 실행

https://tech.ssut.me/2017/08/20/goroutine-vs-threads/

reference: https://stackoverflow.com/questions/14234208/adding-a-hook-to-gunicorn-for-raven-python-sentry-client

$>gunicorn -c your_hook.py

If you only want to convert to specific timezone, use localize. and forget normalize.

just use

tz2 = timezone("Asia/Seoul")
dt = datetime.datetime(year=2017, month=4, day=29, hour=8, minute=35, second=10)
dt2 = tz2.localize(dt)
utc_timestamp = dt2.timestamp()

this will calculate including DST time

but If you are going to do arithmetic operation(- or +) to your datetime object and It crosses DST start or end time,

you should use normalize(dt) to fix the utc offset.

refer to

https://github.com/newvem/pytz/blob/master/pytz/tzinfo.py

def normalize():

How to reference

https://docs.mongodb.com/manual/reference/command/convertToCapped/

But,
1. This command makes db global lock while end this command. It takes several minutes or more according to how many data is stored.
2. This command will remove all indexes of target collection