Pandora的混音

Pandora确实是一个伟大的音乐盒子. 它可以通过用户提供的搜索, 给出风格类似的音乐或者歌手, 也即其网页里宣称的"音乐基因". 同时它还提供"喜欢","讨厌"来选择收听的歌曲是否重复播放.

但是这样的选择会导致某一风格歌曲始终只有那么几首, 即使如何欣赏的歌曲也会在一遍又一遍的播放中产生腻烦. Pandora先前只能通过选择来设定一种风格歌曲的播放,也就所谓的"station", 所以久而久之,我们需要手动地选择或者重新搜索新歌来调换口味. 现在Pandora新提供了QuickMix的功能, 也就是可以在几个stations之间选择播放歌曲, 一定程度上扩展了大家的选择..

NEGF Vs Master Equation

最近在读主方程master equation 相关的文献. 以前不太了解处理开放体系的数学工具还包括
Master Equation, 花了比较大的精力读得都是NEGF相关的文献. 仅仅是因为想当然地认为Weak coupling的器件在实际应用中没有什么用处, 这个想法其实挺愚蠢的, 而实际上来说主方程方法是目前处理开放体系最主要的工具, 特别是在量子光学, 量子测量方面显得特别重要.
在凝聚态体系中, 当然非平衡Green函数NEGF由于在数学上的简洁得到广泛的应用, 很多量子化学计算的也借着所谓的分子电子学之名 推波助澜. 不过, 在R.Car最近一篇文章来看, 处理非平衡态的开放体系,利用基于DFT的NEGF方法在理论上是没有验证的, 他们认为基于TDDFT的主方程方法至少在物理基础上来看是更有前途的.

不为别的, 就为这些话!

这期的Science 围绕丘田事件评论中国兼职教授掠取资源的问题.

有些话, 不管怎么说, 是很有道理的. 就像当初chern说的一样, 只有在本土培养人, 才有希望.

但是, 在国内, 人力资源是廉价的, 如何可能重视人力资源呢 ?

But Yau and other critics insist that the popularity of these programs does not justify the expense. Rather than lavish money on part-time academics, they argue, Chinese institutions should raise stipends of
students and young researchers from their present paltry levels of $30 to $160 a
month. “The Chinese government does not pay enough attention to young people,” Yau
says. As long as the brightest young minds seek greener pastures outside China, the
brain drain—and the hunger for overseas talents—will continue.

量子点, 真是太困难了

没办法, 现在是逼上梁山了.
老板真是无聊的要紧, 除了关心啥最小, 啥尺度之外基本上没有啥物理了.
只好想着法子敷衍他了, 所以,现在觉得跟王胜合作做量子点或许有些意思.
这几天看了量子点的综述和几个人的博士论文, 感觉这个领域真是博大精深啊.

还好, 现在基于carbon nanotube的 量子点 刚做不久, 也有很多比较大的进展, 不过都是荷兰Delft和哈佛macrus组在做, 利用nanotube来define 量子点, 研究所谓的coupling effects Or electron-correlation对体系输运性质的影响.

今天读的综述, 是汉堡一个学者写的, 奇怪的是在isi上搜索他的文章,不到10篇. 不知道是杂志的问题呢, 还是人家就只在德国灌水? 其中, 单纯的Coulomb Blockade效应已经理解的很好, 现在一些open的问题是多量子点间的相互作用, 电-电相互作用对量子点态的作用. 他特别强调所谓的intermediate tunnel coupling的量子点体系的问题很open,而我在查他的文章也发现他最近的工作也是集中这一领域.
但是困难的问题在于他介绍的工具我不太熟悉, 什么Fermi's Golden rule, 看似很简单,但是实际计算是会要人的命诶. 还利用了Keldysh Contour的技术,虽然对这一方法有所了解, 同样是在计算上, 我还没有多少经验.

困难啊...

让人激奋的是,这个领域有很多open的问题, 当然需要勤奋和运气去做些事情了.

texlive 2005的中文配置

按照FerretL 配置说明, 我尝试在RedHat 9.0下配置texlive2005的中文环境.
很顺利地就搞定了,诸如路径等的设置. 但是不能像FerretL声称地实现texexec --pdf *.tex 直接得到中文输出. 正确的中文输出只可以在texexec --output=dvipdf *.tex 实现. 真是诡异,不知道哪里出了问题.

Basic Notions of Condensed Matter Physics的简单书评

在Yamada K 所著Electron Correlation in metals一书中,对P.W. Anderson的名著 Basic notions of condensed matter physics做了几个简短的评论, 很有Anderson的味道.

他提到Anderson在凝聚态物理中的深远影响可以分为两个原理: 一是,对称破缺, 这是相变理论的核心原理, 体系在低温情况出现铁磁态和超导态,即可由该原理解释. 另外一基本原理则是绝热连续, 即我们可以参照简单系统来讨论复杂系统的性质: when we study a generally complicated physical system we can refer to a simple system that contains the esential nature of the real system and understand the complicated systemn on the basis of knowledge of the simple system.

Technorati : BookReview, condensed matter physics

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美国物理学会宣布开放获取物理评论系列杂志

近日美国物理学会(APS)宣布物理评论系列杂志在今年9月份采取开放获取的政策,具体细节如下:

The American Physical Society (APS) is pleased to announce that it will soon expand its Open Access (OA) offerings to articles published in Physical Review A-E, Physical Review Letters, and Reviews of Modern Physics. This OA initiative is called FREE TO READ and, when released in early September 2006, can be applied to any article or group of articles published in the Journals of the American Physical Society back to 1893. Anyone (authors, readers, institutions, funding agencies, etc.) may, by paying a one-time fee, make articles published in our journals available on our sites to all readers at no cost and without a subscription. Readers will have access to PDF and postscript versions of the FREE TO READ articles through the APS online journals.

For years APS has been a leader in OA with its early and continued support of arXiv.org and with its exemplary copyright agreement form. The agreement allows authors to make available their APS publications on their own or their institution's website. APS introduced its first OA journal, Physical Review Special Topics - Accelerators and Beams, in 1998. Based on a sponsorship model, this journal has steadily grown over the past 8 years and is now supported by an international group of accelerator laboratories. APS introduced a second OA journal in 2005 called Physical Review Special Topics - Physics Education Research. This freely available journal is financed by publication charges to the authors or the authors' institutions. The introduction of FREE TO READ extends OA to the articles for all of APS's journals.

The FREE TO READ fees will initially be $975 for articles in Physical Review A-E and $1300 for Letters in PRL. Articles in RMP, due to their large size and the limited number published annually, will be considered on a case-by-case basis. The higher price associated with PRL is due to its higher cost per published Letter (because of its stringent acceptance rate).

The fees will augment revenues for the APS, since they will not be replacing subscriptions, but have been set well below the current amount per article needed to recover costs in the absence of subscriptions. The fees will therefore be adjusted as necessary to maintain APS's ability to sustain this initiative. Additional revenues from FREE TO READ will primarily be used to lower the current subscription rates of the smallest (lowest tier) institutions.

The FREE TO READ initiative represents a path by which APS could gradually transition to full Open Access. If the community (especially institutions and funding agencies) shows continued support for this initiative, a sustainable level may be reached in which the APS can recover its costs, offset its risks, and eliminate subscriptions for some or all of its journals.

The APS is determined to extend every effort to make this model successful. Martin Blume, the Editor-in-Chief, states that "APS is a financially stable organization willing to take risks to support the community," and it is with the community in mind that APS is offering FREE TO READ.

For additional information, please go to the FREE TO READ FAQ at http://publish.aps.org/FREETOREAD_FAQ.html.

Technorati : American Physical Society, Open access, Physical Review

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ZGEMM的手册页

数值计算中, 常用到lapack库zgemm函数,它主要是进行矩阵变换与矩阵乘积的计算. 它的手册页如下 :

ZGEMM performs one of the matrix-matrix operations
*
* C := alpha*op( A )*op( B ) + beta*C,
*
* where op( X ) is one of
*
* op( X ) = X or op( X ) = X' or op( X ) = conjg( X' ),
*
* alpha and beta are scalars, and A, B and C are matrices, with op( A )
* an m by k matrix, op( B ) a k by n matrix and C an m by n matrix.
*
* Parameters
* ==========
*
* TRANSA - CHARACTER*1.
* On entry, TRANSA specifies the form of op( A ) to be used in
* the matrix multiplication as follows:
*
* TRANSA = 'N' or 'n', op( A ) = A.
*
* TRANSA = 'T' or 't', op( A ) = A'.
*
* TRANSA = 'C' or 'c', op( A ) = conjg( A' ).
*
* Unchanged on exit.
*
* TRANSB - CHARACTER*1.
* On entry, TRANSB specifies the form of op( B ) to be used in
* the matrix multiplication as follows:
*
* TRANSB = 'N' or 'n', op( B ) = B.
*
* TRANSB = 'T' or 't', op( B ) = B'.
*
* TRANSB = 'C' or 'c', op( B ) = conjg( B' ).
*
* Unchanged on exit.
*
* M - INTEGER.
* On entry, M specifies the number of rows of the matrix
* op( A ) and of the matrix C. M must be at least zero.
* Unchanged on exit.
*
* N - INTEGER.
* On entry, N specifies the number of columns of the matrix
* op( B ) and the number of columns of the matrix C. N must be
* at least zero.
* Unchanged on exit.
*
* K - INTEGER.
* On entry, K specifies the number of columns of the matrix
* op( A ) and the number of rows of the matrix op( B ). K must
* be at least zero.
* Unchanged on exit.
*
* ALPHA - COMPLEX*16 .
* On entry, ALPHA specifies the scalar alpha.
* Unchanged on exit.
*
* A - COMPLEX*16 array of DIMENSION ( LDA, ka ), where ka is
* k when TRANSA = 'N' or 'n', and is m otherwise.
* Before entry with TRANSA = 'N' or 'n', the leading m by k
* part of the array A must contain the matrix A, otherwise
* the leading k by m part of the array A must contain the
* matrix A.
* Unchanged on exit.
*
* LDA - INTEGER.
* On entry, LDA specifies the first dimension of A as declared
* in the calling (sub) program. When TRANSA = 'N' or 'n' then
* LDA must be at least max( 1, m ), otherwise LDA must be at
* least max( 1, k ).
* Unchanged on exit.
*
* B - COMPLEX*16 array of DIMENSION ( LDB, kb ), where kb is
* n when TRANSB = 'N' or 'n', and is k otherwise.
* Before entry with TRANSB = 'N' or 'n', the leading k by n
* part of the array B must contain the matrix B, otherwise
* the leading n by k part of the array B must contain the
* matrix B.
* Unchanged on exit.
*
* LDB - INTEGER.
* On entry, LDB specifies the first dimension of B as declared
* in the calling (sub) program. When TRANSB = 'N' or 'n' then
* LDB must be at least max( 1, k ), otherwise LDB must be at
* least max( 1, n ).
* Unchanged on exit.
*
* BETA - COMPLEX*16 .
* On entry, BETA specifies the scalar beta. When BETA is
* supplied as zero then C need not be set on input.
* Unchanged on exit.
*
* C - COMPLEX*16 array of DIMENSION ( LDC, n ).
* Before entry, the leading m by n part of the array C must
* contain the matrix C, except when beta is zero, in which
* case C need not be set on entry.
* On exit, the array C is overwritten by the m by n matrix
* ( alpha*op( A )*op( B ) + beta*C ).
*
* LDC - INTEGER.
* On entry, LDC specifies the first dimension of C as declared
* in the calling (sub) program. LDC must be at least
* max( 1, m ).
* Unchanged on exit.

其中开始的两个参数TRANSA/TRANSB用于指定矩阵的操作: 转置,复共厄.

Technorati : lapack, zgemm

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一个函数调用的手记

ZGESV是lapack最简单的一个函数, 即求解线性方程组A*X=B , 子程序调用的格式是zgesv(n, nrh,A, LDA,IPIV,B,LDB,info).
各个参数的意义如下 :
n , 线性方程组的方程数, 也就是矩阵A的阶数;
nrh, 方程组右边的数目, 也即矩阵B的列数;
A,其维度定义为A(LDA,N), 输入时,为方程组的系数矩阵;输出则是LU分解的分式;在计算中基本上不关心A的结果.
LDA,是所谓数组A的起始维数(这里应当认为是矩阵A的第一列的维数),也即矩阵A的行数.
IPIV, 输出参量, 用来定义排列矩阵P的指标.
B, 输入是方程组右边的矩阵B, 维度为B(LDB,NRH);输出是矩阵X(N,NRH)的解, 如果info=0.
LDB, 同LDA, 矩阵B的行数.
info, info=0,表示调用成功返回;非零,则是调用失败.
以下是 zgesv的手册页:

NAME
ZGESV - compute the solution to a complex system of linear equations A * X = B,

SYNOPSIS
SUBROUTINE ZGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO )
INTEGER INFO, LDA, LDB, N, NRHS
INTEGER IPIV( * )
COMPLEX*16 A( LDA, * ), B( LDB, * )
PURPOSE
ZGESV computes the solution to a complex system of linear equations A * X = B, where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
The LU decomposition with partial pivoting and row interchanges is used to factor A as
A=P * L * U, where P is a permutation matrix, L is unit lower triangular, and U is upper triangular. The factored form of A is then used to solve the system of equations A * X = B.

Technorati : lapack, subroutines

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Lapack的命名规则

最近读了读siesta/WanT的源代码, 需要用到Lapack数学库函数库, 随手记下几个常用关键词的含义(也就是所谓的命名规则).

Lapack中有单精度与双精度两种函数选择, 单精度下用s来标志实数,而c标志复数; 双精度下,用d来标志实数, z来标志复数.

其中最主要的关键词是涉及矩阵类型 :

GE , general, 广义矩阵 , 也就是最普遍的矩阵类型;
DI, diagonal, 对角矩阵;
GB, general band,广义带矩阵 ; GT,general triangular,广义三角阵;
HB, Hermitian Band,厄密带矩阵; HE, Hermitian, 厄密阵;
OR, Orthogonal, 正交矩阵;SY,Symmetric, 对称矩阵;
SB, Symmetric Band,对称带矩阵;
ST, Symmetric Triangle,对称三角矩阵;
UN, Unitary,么正矩阵 ....
还有其他很多类型, 基本上这几类的组合,比如general, triangular, symmetric, hermitian, band等...
关键是需要了解这些不同类型矩阵函数之间有什么特点(应该是在计算上可以达到速度等方面的提高).

Technorati : keywords, lapack

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稀疏矩阵的压缩存储

Siesta 对hamiltonian 和overlap hamiltonian 的存储采用稀疏矩阵的压缩格式. 这几天翻了翻稀疏矩阵存储的方案, 了解到最主要的格式是 链表方式, 这样处理对增减非零矩阵元的操作相对容易. 也有采用直接的mapping方案, 但是缺点是增减矩阵元的操作相对复杂.

稀疏矩阵(n X n)的链表存储具体来说就是将矩阵的非零矩阵元(m)按照链表格式存储, 用一个数组(n)按列(或行)的顺序连续存储第一个非零矩阵元的行地址(或列地址), 而非零矩阵元的值/列号(行号)/以及下个非零矩阵元的行(列)地址 则存储在一个3m的数组中. 也就是说一个nXn的矩阵可以map到3m+n的数组上, 从而达到压缩存储目的.

现在不太了解的是, 存储的行/列地址是采用物理地址呢, 还是自己定义一个序列来描述? 印象中在fortran里用指针来处理问题还是不太稳定的.

Technorati : sparse matrix, store scheme

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