x*****o
发帖数: 28 | 1 请教
pappus' centroid theorem在高维(n>3)下是怎么定义或使用的?
V=AS
在高维下,A还是lamina面积,S是轨迹?
如果是轨迹,对规则体,有没有通用的计算轨迹公式?假设知道了lamina
的centroid了...
有么有什么参考书或webpage之类
Thanks in advance! |
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h******g
发帖数: 600 | 2 如果是face to face pi stacking, 一般是不是用centroid to centroid距离来衡量,
这个距离范围是多少?
如果是displaced face to face stacking, centroid to centroid距离一般是多少? 4.2 Å
是不是太远了。
还有edge to face pi stacking 的 H 到 环 centroid的距离范围一般是多少？3.0 Å;
是不是太远。看了一些参考资料，都没有给出明确的答案。哪位高手指点一下
，谢谢了。
还有一个问题，如果是两个苯环在一起形成pi pi stacking，是有功电子基团俩苯环之间
pi pi stacking 作用强，还是连有两个吸电子基团的俩苯环之间的pi pi stacking作用强？
这个看到有个文献讲，吸电子的强，因为电子云密度低，降低了pi electron repulsion，
我不太明白，难道pi pi stacking不需要pi电子云密度高吗？
请指教，谢谢了。 |
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j*****4
发帖数: 292 | 3 Let x,y,z be the length of each interval.
So we have x+y+z=1 (0
(see attachment).If we just want to know the average of each interval,that
is the centroid of x(or y,z)(1/3, according to middle school knowledge).
The average(expectation) of the smallest interval will be x-coordinate of
the centroid of shadowed small triangle.(x
That is 1/3*1/3. |
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u*****o
发帖数: 1224 | 4 是不是求一个底和高都是1的三角形的CENTROID?
那样的话结果也是2/3。
EXPECTATION应该是FIRST MOMENT, SD是SECOND MOMENT,
所以这个求EXPECTATION的应该就是求FIRST MOMENT OF TRIANGLE,就是那个CENTROID的
COORDINATES |
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c****o
发帖数: 1280 | 5 这个没有定论，一般centroid to centroid 3.5 A以内可以认为有比较强的pi pi
interaction，很多人报道面跟面的距离，我以前的组里有个spreadsheet,从每个平面
上选3个点，把坐标输进去就可以算出面跟面的距离，可以自己写一个应该不难。 |
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D**u
发帖数: 204 | 6 max(d'/d) = 2.
Suppose the distance between the centroid and the nearest point is "s", and
the number of points is "n", then ease to see that
d'=d + n*s^2
so d'/d = 1 + n*s^2/d <= 2.
The equality holds if and only if all points lie on a circle, and the
centroid coninsides with the center of the circle. |
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p********a
发帖数: 5352 | 7 ☆─────────────────────────────────────☆
winterwawa (wawa) 于 (Thu Jan 4 09:46:15 2007) 提到:
Data set A: company name, company zip code, zipcode centroides (x, y
coordinates, like longitude and latitude degrees), 50 records
Data set B: all US zip code (including the 50 zipcodes where the companies
are located in A), zipcode centroides (x, y coordinates, like longitude and
latitude degrees. 40000 records
Need to calculate the distance between the company and each US zip code,
meaning total 50 |
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z****4
发帖数: 194 | 8 我在wiki上看到的是这个：
Despite being an easy to understand concept, computing the geometric median
poses a challenge. The centroid or center of mass, defined similarly to the
geometric median as minimizing the sum of the squares of the distances to
each sample, can be found by a simple formula — its coordinates are the
averages of the coordinates of the samples — but no such formula is known
for the geometric median, and it has been shown that no explicit formula,
nor an exact algorithm involving only a... 阅读全帖 |
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e******x
发帖数: 184 | 9 Thanks for the wiki link~ Read it for a while. Thought "procedures that
decrease the sum of distances at each step cannot get trapped in a local
optimum" might help.
I finally made it by sorting the points by decreasing the distance to the
centroid of the points, then computing the sum until the next sum is bigger.
Have no idea if it's definitely correct, but it passed all the test cases... |
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S*******C
发帖数: 822 | 10 http://www.spoj.com/problems/classical/
1 Life, the Universe, and Everything TEST 53195 34.47
2 Prime Generator PRIME1 13334 12.12
3 Substring Check (Bug Funny) SBSTR1 421 10.83
4 Transform the Expression ONP 11720 50.73
5 The Next Palindrome PALIN 5818 10.89
6 Simple Arithmetics ARITH 1405 13.01
7 The Bulk! BULK 257 27.03
8 Complete the Sequence! CMPLS 1314 34.01
9 ... 阅读全帖 |
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t******o
发帖数: 298 | 11 嗯，几何中心这个说法好准确：）
确实，把多数大公司都算上，Sunnyvale基本是centroid。
即便没有公司在Sunnyvale，也是这样的。
把所有软硬件大公司都算上，从Facebook到Cisco到apple。 |
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U****2
发帖数: 168 | 12 千万不要买那个室外桌子。稍微买高一两档次的室内桌。如果经常打，好桌子打的人越
多。如果打的少，经常会调整时间去多打，因为老想着好桌子不打挺浪费的。经历过$
100,$500,$1800的桌子。想起来早就该用那个butterfy centroid. |
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t*******e
发帖数: 216 | 13
yep, 拼音笔误，plowing时身体中心肯定在板间，要不还真成雪山飞狐了。
yes, I take back my words, got confused with another article for hockey
board. centroid should always be emphasized on the upcoming foot, that is
correct.
again, picture is thousand words, video is thousand pictures，看看教程录像一
切都明白。 |
|
a**********u
发帖数: 28450 | 14 Charged-particle multiplicities in pp interactions at View the MathML source
measured with the ATLAS detector at the LHCstar, open, star, openstar, open
121a, 121b, S. Zenz14, D. Zerwas114, G. Zevi della Porta57, Z. Zhan32d, H.
Zhang83, J. Zhang5, Q. Zhang5, X. Zhang32d, L. Zhao107, T. Zhao137, Z.
Zhao32b, A. Zhemchugov65, S. Zheng32a, J. Zhong149, z, B. Zhou87, N. Zhou34,
Y. Zhou149, C.G. Zhu32d, H. Zhu41, Y. Zhu170, X. Zhuang98, V. Zhuravlov99,
B. Zilka143a, R. Zimmermann20, S. Zimmermann20, S... 阅读全帖 |
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z*****e
发帖数: 231 | 15 You cannot use the predictive accuracy to measure the convergence of the
algorithm. Instead, you should use the criteria you are trying to maximize/
minimize. In k-means, I think you can use the total distance of each data
point from the centroids. |
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w*****r
发帖数: 165 | 16 向这里朋友请教一下，怎样估算闭合mesh的centroid.谢谢。 |
|
s***e
发帖数: 911 | 17 Per pixel 大概 200 - 300 nm 尺寸? 如果要到 < 20 nm精度, 至少需要对多少photon
(多少pixels)求平均定Centroid? |
|
s******y
发帖数: 28562 | 18 咦？为什么会被reject呀？我怎么觉得你们的文章的结论挺合理的啊？
我貌似前一阵子听到一个报告关于染色体上的centroid mutation 的，貌似得出了和你的
文章差不多的结论，就是相关变异对所有细胞都是不利因素，也会导致癌细胞生长变慢，
我当时问他是否会导致更高的metastasis/malignancy 比例，他说还没有仔细看这个问
题，不过估计是会。
The
factors
I |
|
t*****m
发帖数: 73 | 19 你的是profile mode的peak吧，就是每个peak实际有很多个点，包括background都有信
号，所以能连起来形成峰。
我的是centroid mode，每个峰提取出来只有一个m/z和一个intensity。没有
background信号(或者有些小峰算noise吧，但不是连成片的那种），连起来的话就是
peak和peak的top连起来了，完全不是Peak了。 |
|
y****o
发帖数: 50 | 20 好多东东，好难，尤其是force, trusses, pulleys, centroids and moments of
intertia那几章，全错。。。哭哭哭555555555555555555
感觉总是没耐心把受力分析画好，然后有的题在FEreviewmanual里在reference book找
不到公式。。。。。。。。。。。。。。。。。。。疯了。。。
跪求大牛指教~ |
|
y*******u
发帖数: 80 | 21 "First, we find the principle direction of the points in a cluster, and
split the cluster by a line orthogonal to the principle direction and go
through
the centroid of the cluster." 其中那个principle direction是个专有名词吗？如果
是，定义是什么？谢谢 |
|
s*******1
发帖数: 146 | 22 find the centroid of a polygon, then combine with the point data, create a
point shapefile, import the shapefile into Geoda, get spatial weight matrix,
you find the distance between two points, then find the shortest one.
location |
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a*********n
发帖数: 1331 | 23 census data作了projection (projected coordinate system)之后，这是metadata的
信息，有问题吗？我是project to projected coordinate system，可是为什么"
extent" 或"bounding coordinates"却是geographic coordinate system? 而且我
create centroids也还是经度纬度的数。可是我需要projected coordinate system
Horizontal coordinate system
Projected coordinate system name: NAD_1983_StatePlane_New_Jersey_FIPS_2900_
Feet
Geographic coordinate system name: GCS_North_American_1983
Details
Map Projection Name: Transverse Mercator
Scale Factor at Central Meridian... 阅读全帖 |
|
y*******u
发帖数: 80 | 24 "First, we find the principle direction of the points in a cluster, and
split the cluster by a line orthogonal to the principle direction and go
through
the centroid of the cluster." 其中那个principle direction是个专有名词吗？如果
是，定义是什么？谢谢 |
|
d******e
发帖数: 7844 | 25 LDA一般情况下就是指Fisher Linear Discriminant.
对于机器学习，一般来说，Dimensionality reduction只是一个提取特征/Feature
Extracion的过程，然后可以配合各种不同的分类器/Classifier。
当然，统计课本里教的Fisher Linear Discriminant是包括分类过程的，其实就是FLD&
Nearest Centroid + L2 distance |
|
y****n
发帖数: 2 | 26 I used ESRI free scripts for ArcView GIS before to get polygon centroids,
etc. the site is http://arcscripts.esri.com/. Hope there is something useful
for |
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s******g
发帖数: 193 | 27 【 以下文字转载自 JobHunting 讨论区 】
发信人: swanking (TJ Max), 信区: JobHunting
标 题: 有在找统计工作的人么？SAS问题求教
发信站: BBS 未名空间站 (Mon Mar 29 12:04:48 2010, 美东)
我导入一个excel文件后进行cluster analysis，导入过程一切顺利，但是不知道怎么
样分析，因为不知道怎么设置变量名。
我的做法是把excel第一行设置成变量名，数据从第二行开始，然后：
proc import datafile="D:\temp\table7_1.xls" out=table7_1 dbms=excel replace;
getnames=yes;
mixed=no;
scantext=yes;
run;
proc cluster data=table7_1 method=centroid simple noeigen rmsstd rsquare
nonorm out=tree;
id sid;
var income educ;
run;
sid income educ都是变量名，但 |
|
f*******i
发帖数: 8492 | 28 我用的是SAS 9.2，参照网上的例子，使用同样的命令行来运行不同的数据，但是输出结果的项目名称
和数量却完全不一样。
人家的输出结果,在“Centroid Hierarchical Cluster Analysis”下有如下几个项目
Variable，Mean，Std，Dev，Skewness，Kurtosis，Bimodality。
而我的输出结果，却只有如下四个项目Eigenvalue，Difference，Proportion，Cumulative。
在“Cluster History”， 人家有NCL，Clusters Joined，FREQ，STD，SPRSQ，RSQ和Dist。
而我的输出结果却只有NCL， cluster joined，FREQ, Norm cent dist,tie。
请问，这是怎么回事啊？ 命令明明是一样的。
|
|
f*******i
发帖数: 8492 | 29 data homework6_1;
set dansas.homework6_1x;
run;
proc cluster data=homework6_1 method=centroid;
id id;
title 'Hierachical Cluster Analysis';
proc tree out = cluster nclusters=4;
Id id;
proc sort;
by cluster;
proc print;
by cluster;
run;
======================================
简单的作业题，我觉得和data无关啊。只不过是variable的数量多少不一样。
而现在的结果却是显示输出项目名称和数量完全不同。 |
|
m******u
发帖数: 277 | 30 总结一下面试被问到的一些问题。
General questions:
- Why are you interested in this position?
- Tell me something about yourself.
- Give me an example how you deal with challenging problems.
- Describe how you deal with multi tasks.
- Show us a writing example that you recently completed.
- What is your career goal in 5 years?
- How do you communicate with your collaborators?
- Have you ever worked on a project in a team? How did you do it?
Technical questions:
- How do you describe your SAS/R skills?
- Where d... 阅读全帖 |
|
c***z
发帖数: 6348 | 31 【 以下文字转载自 DataSciences 讨论区 】
发信人: chaoz (晨钟暮鼓), 信区: DataSciences
标 题: [Data Science Project] Location data quality
发信站: BBS 未名空间站 (Wed Sep 24 14:35:40 2014, 美东)
Hi all,
This is my first project in the new company, and it is about third party
data quality. There is no gold standard for quality, but we know that
repetition of location in the dataset might imply bad quality, because in
this case the location might come from a centroid (e.g. a cell tower, rather
than a cell phone).
There is also no... 阅读全帖 |
|
c***z
发帖数: 6348 | 32 Hi all,
This is my first project in the new company, and it is about third party
data quality. There is no gold standard for quality, but we know that
repetition of location in the dataset might imply bad quality, because in
this case the location might come from a centroid (e.g. a cell tower, rather
than a cell phone).
There is also no ground truth about which datasets are good, but we know
some good ones, particularly the channels we own.
We are exploring the relationship between data quality ... 阅读全帖 |
|
c***z
发帖数: 6348 | 33 Hi all,
This is my first project in the new company, and it is about third party
data quality. There is no gold standard for quality, but we know that
repetition of location in the dataset might imply bad quality, because in
this case the location might come from a centroid (e.g. a cell tower, rather
than a cell phone).
There is also no ground truth about which datasets are good, but we know
some good ones, particularly the channels we own.
We are exploring the relationship between data quality ... 阅读全帖 |
|
l*******s
发帖数: 1258 | 34 首先没搞清你的目标到底是啥？
如果是就把这300个词聚类，那么不难，啥LSA LDA都可以，或者考虑下neutral
network language model，都有现成的实现。
至于evaluation，是个问题，目前要么靠目测，要么算不同k值下每个cluster从
centroid到各个点的距离之和，plot出来，看看拐点在哪，那个k值一般就是最好的。
或者你要是有label的数据，那就用类似classification的方法验证。 |
|
l**p
发帖数: 474 | 35 you could divide them into triangle's
get teh centiod of each triagnel, them get teh weighted average |
|
b****e
发帖数: 1180 | 36 Thank you!
but how to triangulate?
and how to calculate aspect ratio, eccentricity and compactness? |
|
l**p
发帖数: 474 | 37
tehre shoudl some algo for it. need to check on interent. |
|
