When I install ubuntu on a notebook, my windows xp can't be booted. The error message shows that a file named "hal.dll" is missing. After short survey, this error is caused by the windows booter can't find the corresponding partition to boot the xp.
The solution is to edit c:\boot.ini file, and change the partition number to 1, or 2.
You can go to ubuntu to mount the windows xp partition, then edit the file.
星期三, 8月 23, 2006
星期日, 7月 09, 2006
[Computer] How to install multiple versions of GCC
How to install multiple versions of GCC
It may be desirable to install multiple versions of the compiler on the same system. This can be done by using different prefix paths at configure time and a few symlinks.
Basically, configure the two compilers with different --prefix options, then build and install each compiler. Assume you want "gcc" to be the latest compiler and available in /usr/local/bin; also assume that you want "gcc2" to be the older gcc2 compiler and also available in /usr/local/bin.
The easiest way to do this is to configure the new GCC with --prefix=/usr/local/gcc and the older gcc2 with --prefix=/usr/local/gcc2. Build and install both compilers. Then make a symlink from /usr/local/bin/gcc to /usr/local/gcc/bin/gcc and from /usr/local/bin/gcc2 to /usr/local/gcc2/bin/gcc. Create similar links for the "g++", "c++" and "g77" compiler drivers.
An alternative to using symlinks is to configure with a --program-transform-name option. This option specifies a sed command to process installed program names with. Using it you can, for instance, have all the new GCC programs installed as "new-gcc" and the like. You will still have to specify different --prefix options for new GCC and old GCC, because it is only the executable program names that are transformed. The difference is that you (as administrator) do not have to set up symlinks, but must specify additional directories in your (as a user) PATH. A complication with --program-transform-name is that the sed command invariably contains characters significant to the shell, and these have to be escaped correctly, also it is not possible to use "^" or "$" in the command. Here is the option to prefix "new-" to the new GCC installed programs:
--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
With the above --prefix option, that will install the new GCC programs into /usr/local/gcc/bin with names prefixed by "new-". You can use --program-transform-name if you have multiple versions of GCC, and wish to be sure about which version you are invoking.
If you use --prefix, GCC may have difficulty locating a GNU assembler or linker on your system, GCC can not find GNU as/GNU ld explains how to deal with this.
Another option that may be easier is to use the --program-prefix= or --program-suffix= options to configure. So if you're installing GCC 2.95.2 and don't want to disturb the current version of GCC in /usr/local/bin/, you could do
configure --program-suffix=-2.95.2
This should result in GCC being installed as /usr/local/bin/gcc-2.95.2 instead of /usr/local/bin/gcc.
It may be desirable to install multiple versions of the compiler on the same system. This can be done by using different prefix paths at configure time and a few symlinks.
Basically, configure the two compilers with different --prefix options, then build and install each compiler. Assume you want "gcc" to be the latest compiler and available in /usr/local/bin; also assume that you want "gcc2" to be the older gcc2 compiler and also available in /usr/local/bin.
The easiest way to do this is to configure the new GCC with --prefix=/usr/local/gcc and the older gcc2 with --prefix=/usr/local/gcc2. Build and install both compilers. Then make a symlink from /usr/local/bin/gcc to /usr/local/gcc/bin/gcc and from /usr/local/bin/gcc2 to /usr/local/gcc2/bin/gcc. Create similar links for the "g++", "c++" and "g77" compiler drivers.
An alternative to using symlinks is to configure with a --program-transform-name option. This option specifies a sed command to process installed program names with. Using it you can, for instance, have all the new GCC programs installed as "new-gcc" and the like. You will still have to specify different --prefix options for new GCC and old GCC, because it is only the executable program names that are transformed. The difference is that you (as administrator) do not have to set up symlinks, but must specify additional directories in your (as a user) PATH. A complication with --program-transform-name is that the sed command invariably contains characters significant to the shell, and these have to be escaped correctly, also it is not possible to use "^" or "$" in the command. Here is the option to prefix "new-" to the new GCC installed programs:
--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
With the above --prefix option, that will install the new GCC programs into /usr/local/gcc/bin with names prefixed by "new-". You can use --program-transform-name if you have multiple versions of GCC, and wish to be sure about which version you are invoking.
If you use --prefix, GCC may have difficulty locating a GNU assembler or linker on your system, GCC can not find GNU as/GNU ld explains how to deal with this.
Another option that may be easier is to use the --program-prefix= or --program-suffix= options to configure. So if you're installing GCC 2.95.2 and don't want to disturb the current version of GCC in /usr/local/bin/, you could do
configure --program-suffix=-2.95.2
This should result in GCC being installed as /usr/local/bin/gcc-2.95.2 instead of /usr/local/bin/gcc.
星期一, 3月 27, 2006
[Computer] Windows XP no sound
sometimes, the windows xp 's sound device is disappear.
You can go to control panel to [Add new hardware], then choose a sound device...e.g., "Microsoft" MPU-401 compatible devices..
And then reboot....
You will see your favorite sound device comes back and works again...... if you are lucky..
I am the lucky one.
You can go to control panel to [Add new hardware], then choose a sound device...e.g., "Microsoft" MPU-401 compatible devices..
And then reboot....
You will see your favorite sound device comes back and works again...... if you are lucky..
I am the lucky one.
星期二, 3月 21, 2006
星期二, 10月 05, 2004
[Network] ns2 除錯
原文http://kunlung.csie.org/ns2_experience.html
☆用 gdb 來 debug
使用gdb (GNU debugger)可以對debug更有幫助，
例如難解的segmentation fault
不過ns-2.1b9目錄需要重新compile
編輯 Makefile.in
找到底下兩行
$(CPP) -c $(CFLAGS) $(INCLUDES) -o $@ $*.cc
$(CC) -c $(CFLAGS) $(INCLUDES) -o $@ $*.c
改成
$(CPP) -g3 -c $(CFLAGS) $(INCLUDES) -o $@ $*.cc
$(CC) -g3 -c $(CFLAGS) $(INCLUDES) -o $@ $*.c
執行 ./configure
./make
(因為compiler依據Makefile.in產生Makefile,
若改在Makefile則無效)
完成後，可以這樣使用(我的tcl放在 ~ns/examples )
gdb ../ns
(進入gdb畫面)
r kiwi.tcl
或是 r kiwi.tcl > log1 (r即為run)
通常程式中斷時，用backtrace 可以查呼叫關係
另外b(breakpoint)可以設中斷點
設中斷點的方法：
打 gdb ../ns 之後
進入gdb 命令提示列
打 b [路徑][檔案名]:[行號]
例如：
b mac/mac802_15_3.cc:1500
就是把中斷點設在mac802_15_3.cc的第1500行最容易錯的地方在於路徑
gdb的current work directory 是執行檔的那個目錄
因為我們是執行ns
所以工作目錄應該是 ns-2.1b9
所以若我要debug mac目錄裡的檔案，前面就要加 "mac/"
設好中斷點後
r XXX.tcl 便開始執行
遇到中斷點就停下來
這時可以用n (代表next)一行一行的執行配合中斷點
還可以加上條件式中斷
語法：
condition N EXPRESSION
N是中斷點的編號
EXPRESSION是一個敘述句
例如
condition 1 Scheduler::instance ().clock > 1.044412
就是說當時間超過1.044412且到達1號中斷點才中斷
gdb真的很強
EXPRESSION 怎麼寫都有效... :P☆常見的 bug 訊息與原因
以下列出在make時常遇見的錯誤訊息的原因：
Scheduler: Event UID not valid!
這是scheduler物件的錯誤訊息
最常的可能是有一個timer物件，還沒有expire而你又呼叫它的start function
可能發生在你寫了新的timer物件，或是你更改了原作者的程式流程
中止在一點也沒有錯的程式區段
可能是你新增了新的data member在.h裡
因為交叉include而沒有被compile到
這時試試看 make clean; make
常常就OK了Segmentation Fault
最常發生的原因是指標所指的物件不存在，或是traverse陣列時跑到陣列外面去了
[Academic] Zipf, Power-laws, and Pareto
Zipf, Power-laws, and Pareto是在Paper上常常見到。這三個名詞常用來描述一個現象"large events are rare, but small ones quite common"。例如，大的地震發生次數很少，小的地震發生次數確很多。大都市很少，小的鄉鎮很多。一些字很少見，但一些字則常常出現(如 'and' and 'the' ).
Reference: http://ginger.hpl.hp.com/shl/papers/ranking/ranking.html
Zipf's law 通常用來描述一個事件發生的數量或頻率( 'size')跟它的排名(rank) r有關. George Kingsley Zipf一位語言學家想找出某英文字出現的頻率有多高，例如 3rd 或 8th或100th常見字出見的次數。Zipf's law指出事件出現的頻率y跟它的排名(rank) r成反比:
y ~ r^-b, with b close to unity.
Pareto則是對大家的收入(income)分佈有興趣。相對於想知道第r個人的收入，Pareto想知道有多少人的收入大於x. Pareto's law使用累積分佈(cumulative distribution function (CDF))來找出分佈狀況。, i.e. the number of events larger than x is an inverse power of x:
P[X > x] ~ x^-k.
Pareto指出只有少數人是億萬富翁，大部分的人都是沒有錢的。
Power law distribution對有多少人的收入大於x不感興趣，相對的，它對有多少人收入洽好是x感興趣. It is simply the probability distribution function (PDF) associated with the CDF given by Pareto's Law. This means that
P[X = x] ~ x^-(k+1) = x^-a.
That is the exponent of the power law distribution a = 1+k (where k is the Pareto distribution shape parameter).
近年來，很多學者發現internet顯示出很多符合power-law distributions的現象: the number of visits to a site, the number of pages within a site, and the number of links to a page, to name a few.
圖1a展示了AOL users'訪問不同網站的圖形on a December day in 1997. 從圖中，可以發現只有很少的網站有超過2000位訪客, 大多數的網站只有很少的訪客 (70,000 網站只有一位訪客). The distribution is so extreme that if the full range was shown on the axes, the curve would be a perfect L shape. Figure 1b below shows the same plot, but on a log-log scale the same distribution shows itself to be linear. This is the characteristic signature of a power-law.
Fig. 1a Linear scale plot of the distribution of users among web sites
Fig. 1b Log-log scale plot of the distribution of users among web sites
Let y = number of sites that were visited by x users.
In a power-law we have y = C x-a which means that log(y) = log(C) - a log(x)
So a power-law with exponent a is seen as a straight line with slope -a on a log-log plot.
總結，Zipf, Power-laws, and Pareto都是在描述同一個現象，只是用不同的觀點罷了。
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