h******g
发帖数: 11250 | 1 SNR的定义好像有点问题
* Signal-to-noise ratio (SNR) defines the purity of the output signal
and gives direct information about the camera’s ability to reproduce a
signal. In a logarithmic scale, it is expressed in decibels (dB), and is
obtained from the following formula:
SNR=20log10(mean/std)
SNR is independent of any gain applied to the signal since signal and noise
are equally amplified.
相机里的噪音主要应该是暗电流(DC)，随时间线性增长，而std随时间应该是sqrt增长 |
|
r******x
发帖数: 5965 | 2 Dynamic range, abbreviated DR or DNR,[1] is the ratio between the largest
and smallest possible values of a changeable quantity, such as in sound and
light. It is measured as a ratio, or as a base-10 (decibel) or base-2 (
doublings, bits or stops) logarithmic value. |
|
e**n
发帖数: 5876 | 3 对, dxo解释了normalized后SNR和absolute SNR的区别. dxo的结论是对于比较不同相
机的高感, 是"only normalized results are relevant." 也就是只有normalized后
SNR才有意义. absolute SNR是irrelevant的.
版上这么多童鞋都采用了dxo的sensor测试结果, 为什么就不理解dxo的测试方法呢?
如果不理解dxo的测试方法, 那么dxo的sensor测试结果就完全没有意义
dxo给了数学公式的计算的normalized的结果,
"What should be remembered is that doubling the resolution adds:
3dB to the normalized SNR
0.5 bit to the normalized DR
0.5 bit to the normalized TR
1.5 bit to the normalized CS.
"
这个公式很清楚了,就是说:
如果2个sensor的单个像素大小一样, 如果sensor X的面积是s... 阅读全帖 |
|
a**********u
发帖数: 28450 | 4 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 |
|
H**r
发帖数: 10015 | 5
> About us
ABOUT US
Your gateway to World Universities and Colleges
4 International Colleges & Universities is an international higher education
search engine and directory reviewing accredited Universities and Colleges
in the world. 4icu.org includes 10,000 Colleges and Universities, ranked by
web popularity, in 200 countries.
Being a non-paid directory, 4icu.org is free of charge to both visitors and
organisations included. No registration is also required.
Organizations included
The ... 阅读全帖 |
|
a****5
发帖数: 10854 | 6 pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion
activity, aH+, in a solution
proton在哪里？
那个p是proton的意思？ 你这化学式体育老师教的。。。 |
|
b*s
发帖数: 82482 | 7 你这个片面理解，太差了
pH是 proton concentration的负对数
pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion
activity, aH+, in a solution
proton在哪里？
那个p是proton的意思？ 你这化学式体育老师教的。。。 |
|
|
n*********2
发帖数: 357 | 9 》【 在 ipad4 (Apple) 的大作中提到: 】
》 : 1，一旦量子计算机搞出来了， 这些既有方案绝大部分都会完蛋。
》 : 为什么？ 可以解释一下吗？
已经有很有效的量子算法来攻击 RSA, Discrete Logarithm, 和椭圆曲线公钥。
只有很少的公钥还没有有效的量子攻击。
》 : 2， 于是有人就忽悠量子密钥交换。如果你仔细研究一下量子密钥交换， 你就会
发现
》 : ， 当传统的公钥都完蛋的时候，量子密钥交换协议也不工作了
》: 这里又是为什么？ 也麻烦简单解释一下可以吗？
这个比较复杂。 要首先理解量子密钥交换协议。 建议首先读一下 The Code Book 这
本书。 很好的一本科普书， 可读性非常好。 |
|
|
r***u
发帖数: 241 | 11 http://www.cra.org/Activities/awards/undergrad/2005.patrascu.html
Mihai Patrascu is a junior at MIT, where he majors in Mathematics with
Computer Science.
Mihai's research is in the area of data structures and algorithms. Mihai
has solved three major open problems over his three years at MIT: in
his freshman year, he solved a problem in data structures that had
remained open for the last 20 years—tight upper and lower bounds on the
partial-sums problem; in his third semester, he proved logarithm |
|
|
t*d
发帖数: 1290 | 13 a = log(b*c*d*e*f)
AND
a = log(a) + log(b) + log(c) + log(f)
Which code is faster?
Thx! |
|
a**a
发帖数: 416 | 14 The former is faster, but the other is more stable from overflow. |
|
a******e
发帖数: 95 | 15 Modern compilers will consider them the same. |
|
t*****n
发帖数: 4908 | 16 http://www.sgi.com/tech/stl/SortedAssociativeContainer.html
A Sorted Associative Container is a type of Associative Container. Sorted
Associative Containers use an ordering relation on their keys; two keys are
considered to be equivalent if neither one is less than the other. (If the
ordering relation is case-insensitive string comparison, for example, then
the keys "abcde" and "aBcDe" are equivalent.)
Sorted Associative Containers guarantee that the complexity for most
operations is never worse... 阅读全帖 |
|
c*******h
发帖数: 1096 | 17 It may not worth the efforts. Since binomial coefficients grow fast,
it is quite unlikely that you can write a general purpose routine to
compute large coefficients. Know your objective before coding. For
example, if you only need a few digits of accuracy, use double
precision in combination with logarithm mapping. On the other hand,
if you need an accurate integral result, determine the number of
digits of the result before choosing the accurate integer data type. |
|
c*******h
发帖数: 1096 | 18 It may not worth the efforts. Since binomial coefficients grow fast,
it is quite unlikely that you can write a general purpose routine to
compute large coefficients. Know your objective before coding. For
example, if you only need a few digits of accuracy, use double
precision in combination with logarithm mapping. On the other hand,
if you need an accurate integral result, determine the number of
digits of the result before choosing the accurate integer data type. |
|
s*****t
发帖数: 1994 | 19 Logarithmic Spirals Isabel and M51
Credit: Comparison and M51 image copyright Brian Lula; Hurricane Isabel, courtesy GHCC, NASA
Explanation: Uncomfortably close hurricane Isabel (left) and 30 million light-year distant galaxy M51 actually
don't have much in common. For starters, Isabel was hundreds of miles across, while M51 (the Whirlpool
Galaxy) spans about 50,000 light-years making them vastly dissimilar in scale, not to mention the extremely
different physical interactions which control |
|
s********3
发帖数: 231 | 20 《科学》对STAP手稿的专家评审意见曝光
《科学》对传说中的STAP细胞论文的三名评审专家意见，过去一直被雪藏，今天终于
被曝光。专家对这一研究的评价不高，认为非常全面的描述性研究，如果结果确定，可
能导致发育生物学大厦的颠覆，其实是不相信这种研究结论。因为没有当时的投稿件，
所以没有办法对这些评价进行更深入分析。不过这些资料显然都在某个地方，只是拥有
的人不愿意拿出来。
Retraction Watch readers are of course familiarwith the STAP stem cell saga,
which was punctuated by tragedy last month whenone of the authors of the
two now-retracted papers in Nature committed suicide.
In June, Science‘s news section reported:
Sources in the scientific community confirm that early version... 阅读全帖 |
|
k****r
发帖数: 222 | 21
in gsm, I guess there is only one solution, you can setup
the configuration let some of those controlling channels (signaling,
broadcasting, etc) being able to allocated to voice channel upon
request, very limited tho.
in cdma, should be no problem, theoriotically there could be
unlimited simutaneous calls going through within one cell/bandwidth,
just the voice path quality will drop logarithmicly, that's called
QoS negotiable.
correct me if I was wrong. |
|
h**********a
发帖数: 40 | 22 No. 1: First and Second Law of Macroeconomics:
1) Linearity of Logarithm: log (A+B) = log (A) + log (B)
2) Jensen's Equaliy: E[f(X)] = f(E[X])
No. 2: Why does a lady refuse to marry a Bayesian statistician?
Because he only cares about her *posterior* distribution. |
|
B****n
发帖数: 11290 | 23 maybe you can use law of iterated logarithm for Brownian motion to prove it.
Consider when t approaches infinity, Nt should approach t or something. |
|
j******n
发帖数: 271 | 24 taking logarithm on both sides for all equations turns the set to a a set of
linear equations, with coefficients in C (some may be complex numbers). |
|
c**i
发帖数: 6973 | 25 Edward Rothstein, Masters of Math, From Old Babylon; A precursor to the
theoretical flowering of Greek math. New York Times, Nov. 27, 2010.
http://www.nytimes.com/2010/11/27/arts/design/27tablets.html?_r=1&scp=3&sq=cuneiform&st=cse
Note:
(a) Pythagoras (c. 570- c. 495 BC)
Wikipedia
(b) The report states, "But Neugebauer, and then his many students and rivals, also showed how sophisticated Babylonian mathematics was and how many similarities existed to later Western systems if, that is, you count... 阅读全帖 |
|
t**********m
发帖数: 205 | 26 来自主题: Mathematics版 - 伟哥之乐 The joy of viXra
https://telescoper.wordpress.com/2011/05/19/
Posted in The Universe and Stuff with tags arXiv, astronomy, Cosmology,
Physics, scientific publishing, viXra on May 19, 2011 by telescoper
From time to time on this blog I post rants about the state of scientific
publishing, open access, the importance of the arXiv for astronomy and
cosmology, and so on.
This morning, however, I discovered an “alternative” side to the whole
business of online science, a site by the name of viXra. Mos... 阅读全帖 |
|
F*******n
发帖数: 8 | 27 The following is copied from p.622 of Siu's 1988 Annals paper "The Existence
of Kahler-Einstein...". Siu is really angry at Tian's plagiarism.
Added after submission of paper. I presented the results and methods of this
paper in the Geometry and Analysis Conference at Columbia University in
April, 1986. G. Tian in August, 1986 wrote a paper "On Kihler-Einstein
metrics on certain Kihler manifolds with cl(M) > 0" (Invent. Math. 89 (1987)
, 225-246) in which he constructed Kdhler-Einstein metrics f... 阅读全帖 |
|
v*********n
发帖数: 573 | 28 田院士曰：“窃idea不算偷”。
The following is copied from p.622 of Siu's 1988 Annals paper "The Existence
of Kahler-Einstein...". Siu is really angry at Tian's plagiarism.
Added after submission of paper. I presented the results and methods of this
paper in the Geometry and Analysis Conference at Columbia University in
April, 1986. G. Tian in August, 1986 wrote a paper "On Kihler-Einstein
metrics on certain Kihler manifolds with cl(M) > 0" (Invent. Math. 89 (1987)
, 225-246) in which he constructed Kdhler-... 阅读全帖 |
|
s*****V
发帖数: 21731 | 29 【 以下文字转载自 Military 讨论区 】
发信人: saturnV (土星五号), 信区: Military
标 题: 刘克峰：知识，技巧与想象力
发信站: BBS 未名空间站 (Sun Jun 9 01:14:57 2013, 美东)
在国内工作一年多，接触了许多中学生，大学生和研究生。为了吸引优秀的学生到数学
中来，我与他们有了许多的对话与交流，这引发了我对数学教育从各方面的思考。迄今
已有许多文章对我们的教育体制提出批评，认为它扼杀了学生们的想象力。但我觉得我
们的教育从中学起就过分强调技巧，根本没有开拓学生的知识面才是根本的弊病。见多
才能识广，而没有宽广的知识面，想象力就是无源之水。在中学里，以奥数为甚的题海
战术使学生忘记了做题的目的是为了理解知识。在大学里，有些老师的知识就过于陈旧
和狭窄，将学生引入死胡同，更不可能拓宽学生的知识面了。我觉得对数学专业的学生
而言，要首先拓宽眼界，不仅在数学里的各个学科之间，更包括物理等相关学科。种种
感想促成了这篇文章，希望我自身的经历与体会能起到抛砖引玉的作用。
我将结合自己的治学经验讨论一下知识的重要性以及知识，技巧与想... 阅读全帖 |
|
L*m
发帖数: 235 | 30 最近十年在annals of mathematics上发表或合作发表文章的华人全统计（不包括
terrence tao和一位mit本科毕业的abc华人），单位统计以现在作者单位为准
annals
2015年
A proof of Demailly’s strong openness conjecture
关启安（北京大学） 周向宇（中科院）
A solution of an L2 extension problem with an optimal estimate and
applications
关启安（北京大学） 周向宇（中科院）
Finsler metrics and Kobayashi hyperbolicity of the moduli spaces of
canonically polarized manifolds
杨世琪（普渡大学） Wing-Keung To（新加坡国立大学）
Construction of Cauchy data of vacuum Einstein field equations evolving to
black holes
黎俊彬（中山大学）... 阅读全帖 |
|
L*m
发帖数: 235 | 31 近十年ACTA上华人作者统计
ACTA
2014
Gromov–Hausdorff limits of Kähler manifolds and algebraic geometry
Simon Donaldson, Song Sun（孙崧，stony brook）
Geometric quantization for proper moment maps: the Vergne conjecture
Xiaonan Ma（麻小南 法国巴黎第七大学）, Weiping Zhang（张伟平 南开大学）
2013
p-adic logarithmic forms and a problem of Erdős
Kunrui Yu（香港科技大学）
2012
2011
2010
2009
The quantum orbifold cohomology of weighted projective spaces
Tom Coates, Alessio Corti, Yuan-Pin Lee（李元斌 犹他大学）, Hsian-Hua Tseng
（曾祥華 俄亥俄）
2008
Qu... 阅读全帖 |
|
x********i
发帖数: 905 | 32 http://iccm.mcm.ac.cn/dct/page/1
Plenary Lectures
Group 1
Wei Zhang: RTF and L-functions
Kai-Wen Lan: Cohomology of automorphic bundles
Xinyi Yuan: On Faltings heights of CM abelian varieties
Jing Yu: On Linear Independence of Logarithms
Xuhua He: Cocenter of Hecke algebras
Jiu-Kang Yu: A GAGA theorem for p-adic groups
Jianya Liu: Manin's conjecture for a class of singular cubic
hypersurfaces
Lei Fu: Rigidity of $ell$-adic Sheaves
Si Li: Open-closed topologica... 阅读全帖 |
|
t**********6
发帖数: 565 | 33 The company is located at Twin City, MN. The company size should be over $1
billion. This project manager position will require to be able to speak
Chinese and travel to China and other Asian country. drop me a message if
you think you are qualified and interested.
Design/Build Project Manager - International (Mandarin Chinese Fluency)
Our client’s name is synonymous with technologically sophisticated, high-
production machinery in the railway industry. The company's reputation for
producing s... 阅读全帖 |
|
|
t******n
发帖数: 6242 | 35 今天无聊，看到这篇无聊的文章，就给你无聊地翻译成英文吧。
探索星系的捷径
A Shortcut to Galaxy Exploration
1. 问苍天情为何物？
1. Ask what love is heaven?
有人类的历史以来，人类就不断地探索自然，扩展了解自然的疆界。哥伦布发现新大陆
就是最好的例子。人类探索自然的勇气是从哪儿来的呢？来自人类情感的力量。那么，
情感是什么东西呢？这是千万年来，文学家探索的主题。在有一些文学家的眼中，物理
学家是没有情感的冷血动物。我就是一个物理学家。但是，我一点也不埋怨这些文学家
。虽然物理学家在自然界的探索中做出了伟大的贡献，但是，物理学家从来就没有给出
情感的物理定义是什么，也没有找到自然界蕴含情感的丝毫证据。所以，虽然人类知道
自己的生存发展跟自然环境是密不可分的，但是，很少有人类表达出对自然环境感谢的
情感。在很多人的眼中，自然界是死亡无情的物质世界。中国有一句古语，叫做“天若
有情天亦老”。因为几乎所有人类相信天是不老的，所以，认为苍天是没有情感的，就
不足为奇了。我提出了一个宇宙生长衰老的模型。虽然这个模型及其简单，能解释大多
... 阅读全帖 |
|
t**********m
发帖数: 205 | 36 The joy of viXra
https://telescoper.wordpress.com/2011/05/19/
Posted in The Universe and Stuff with tags arXiv, astronomy, Cosmology,
Physics, scientific publishing, viXra on May 19, 2011 by telescoper
From time to time on this blog I post rants about the state of scientific
publishing, open access, the importance of the arXiv for astronomy and
cosmology, and so on.
This morning, however, I discovered an “alternative” side to the whole
business of online science, a site by the name of viXra. Mos... 阅读全帖 |
|
d*******n
发帖数: 524 | 37 Have no idea what you guys were talking about here.
So I just derived it myself.
Here I use the lowercase s to represent the logarithm of stock price:
s = ln(S)
and use v to represent the value of the derivative.
then under GBM assumption for the stock price:
s = (r-1/2sigma^2)t + sigma*W
which is a biased Brownian Motion.
(Note: this W is a BM only in the risk-neutral probability space,
not the real probability space. All the following BMs,
expectations and Martingales are in the risk-neutral s |
|
p*****k
发帖数: 318 | 38 they follow a logarithmic spiral and meet at the center. the distance
traveled is same as the side length of the square. |
|
c****c
发帖数: 29 | 39 For each of the following utility functions find the marginal utility and sh
ow that it is increasing at a decreasing rate. Mathematically, U'(W)>0 and U
''(
W)<0. Also graph each function to verify your results.
Exponential U(W)=e^(-AW)
Logarithmic U(W)=ln(W)
Quadratic U(W)=W-0.5AW^2
Power U(W)=(B/(B-1))*W^(1-1/B)
Describe a risk averse, a risk seeking and risk neutral investor.
what shape would the utility function of each be in risk-return space?
which best |
|
p***i
发帖数: 96 | 40 没有人证明过这个问题吗？？？
gbm模型里假设Logarithmic return是normal dist'n，直接造成了这个非均匀的抛硬币
游戏。 |
|
M****i
发帖数: 58 | 41 You are welcome.
Generally speaking, the martingale convergence theorem can not be applied
here because I(t) is only a semimartingale, not a martingale:
I(t)=g(t)*M(t),
where
g(t)=exp(-\int_0^t c(r)dr)
M(t)=\int_0^t c(s)*exp(\int_0^s c(r)dr) dB(s).
Note that g(t) is of finite variation and only M(t) could be a martingale.
This can also be verified by my previous example
c(t)=1/(1+t). In this case I(t)=B(t)/(1+t), which is not a martingale, but
it converges to 0 a.s. by iterated logarithm.
For yo... 阅读全帖 |
|
x******a
发帖数: 6336 | 42 11. a. law of the iterated logarithm.
b. weak law of large numbers.
c. P(|B_t/t|> x)=P(|B_1|>\sqrt{t}x)\to 0 for any x>0.
13 E(S_t)=E(S_0). lim(S_t)=0 (assuming \sigma is a nonzero constant) because
sigma*B_t-\sigam^2t/2 ->-\infty. |
|
l*******l
发帖数: 248 | 43 wiki了一下，那个必须是natural logarithm吧？ |
|
M****i
发帖数: 58 | 44 You could try the following idea to see whether it helps.
Let b(t,s)=c(s)a(t,s), (d/ds)b(t,s)=f(t,s), h(t)=(2tlnlnt)^(1/2) and T>e.
Then integration by parts gives for t>T,
I(t)=b(t,t)W(t)-\int_0^t W(s)f(t,s) ds
=(b(t,t)h(t))*(W(t)/h(t))-\int_0^T W(s)f(t,s) ds-\int_T^t (W(s)/h(s))*(f(t,s)h(s)) ds.
Observe that for t>=T, W(t)/h(t) is bounded a.s. by iterated logarithm of BM, hence a
sufficient condition to ensure that I(t) tends to zero a.s. is that
b(t,t)h(t), \int_0^T |f(t,s)| ds and \int_T^t |... 阅读全帖 |
|
g********r
发帖数: 8017 | 45 每次一提数据分析，陈老师就说一大堆废话搪塞过去。时间长了我就相信他根本没有写
出程序来。要是他早做个分析，没人会攻击他。
of
logarithm |
|
|
s****h
发帖数: 3979 | 47 今天无意在kaggle上发现了这道题，要预测CTR rate：
https://www.kaggle.com/c/avazu-ctr-prediction
不利的一点是这题已经出来两个多月，还有2周就截止了。
有趣的是这题变量很多，啥machine learning的tool都可以随便试，所以目前已经提交
答案的队居然有1400+，估计都是啥顺手的toolbox都拿来试一试。
论坛上看到很多人说直接用Vowpal Wabbit,还没tuning呢，结果就接近目前排名最高的
team了。
大家有兴趣的一起看看？分享一下思路？
evaluation is based on Logarithmic Loss.
觉得不合理啊，实际应用中应该用number of correct prediction吧。
下午比较空，就下载了数据，load进hive，先算了算group by各个变量的CTR。
我目前的思路比较too simple too naive。就是每个变量替换成该group by变量的CTR
，然后general linear regression试试看效果如何。 |
|
s****h
发帖数: 3979 | 48 今天无意在kaggle上发现了这道题，要预测CTR rate：
https://www.kaggle.com/c/avazu-ctr-prediction
不利的一点是这题已经出来两个多月，还有2周就截止了。
有趣的是这题变量很多，啥machine learning的tool都可以随便试，所以目前已经提交
答案的队居然有1400+，估计都是啥顺手的toolbox都拿来试一试。
论坛上看到很多人说直接用Vowpal Wabbit,还没tuning呢，结果就接近目前排名最高的
team了。
大家有兴趣的一起看看？分享一下思路？
evaluation is based on Logarithmic Loss.
觉得不合理啊，实际应用中应该用number of correct prediction吧。
下午比较空，就下载了数据，load进hive，先算了算group by各个变量的CTR。
我目前的思路比较too simple too naive。就是每个变量替换成该group by变量的CTR
，然后general linear regression试试看效果如何。 |
|
z****8
发帖数: 13 | 49 特征工程简介
原文链接：
http://mp.weixin.qq.com/s?__biz=MzIzODExMDE5MA==&mid=403826129&
（I）特征工程可以解决什么样的问题？
特征工程是一个非常重要的课题，是机器学习中不可缺少的一部分，但是它几乎很少出
现于机器学习书本里面的某一章。在机器学习方面的成功很大程度上在于如果使用特征
工程。在机器学习中，经常是用一个预测模型（线性回归，逻辑回归，SVD等）和一堆
原始数据来得到一些预测的结果，人们需要做的是从这堆原始数据中去提炼较优的结果
，然后做到最优的预测。这个就包括两个方面，第一就是如何选择和使用各种模型，第
二就是怎么样去使用这些原始的数据才能达到最优的效果。那么怎么样才能够获得最优
的结果呢？贴上一句经典的话就是：
Actually the sucess of all Machine Learning algorithms depends on how you
present the data.
—— Mohammad Pezeshki
直接翻译过来便是：事实上所有机器学习算法上面的成功都在于你怎么样去展示这些数
... 阅读全帖 |
|
|
