q****q
发帖数: 2 | 1 我想做一个Simulation,需要把z-matrix internal coordinate 转换成Cartesian
coordinate. 希望得到各位前辈指点。 |
|
w*******U
发帖数: 256 | 2 i programmed two codes using staggered and collocated grids to solve the
incompressible N-S equation in a Cartesian box with no-slip boundary
condition (lid driven flow). i used predictor-corrector method to decouple
velocity and pressure and imposed zero normal gradient for pressure boundary
condition in both codes. in the code of staggered grids, everything is fine
whereas in the code of collocated grids the velocity is fine but the
pressure drops always and cannot converge. could anyone help ... 阅读全帖 |
|
r****y
发帖数: 1437 | 3 这个验算一下就知道了吧，给定时间地点，从约定的东方算起，看是多少度，
然后看它的是多少度，就知道从哪儿定义的了。
我猜多半是local cartesian坐标系下向东为0 saa
这还算好的了，猫腻更多的我都见过。 |
|
o****l
发帖数: 21 | 4 If you choose the principle axes as your cartesian coordination axes or
you only consider the principle stresses, there are only fxx, fyy, and fzz,
3 non-zero stresses. In strength of materials, people use the matrix form of
stress tensor for general conditions. It's very easy to use rotation matrix
to translate the general stress matrix to a diagonal matrix to get the 3
principle stresses. Mathematicall, it's very convinent and you do not need
to use the formula which relate the general stres |
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z**e
发帖数: 10 | 5 Suppose A is countable set :
A * A *A .....stands for infinite Cartesian product of A , is the product
countable?
How to prove ? |
|
H****h
发帖数: 1037 | 6 No.
Suppose A is countable set :
A * A *A .....stands for infinite Cartesian product of A , is the product
countable?
How to prove ? |
|
q****q
发帖数: 2 | 7 我想做一个Simulation,需要把z-matrix internal coordinate 转换成Cartesian
coordinate. 希望得到各位前辈指点。 |
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p**y
发帖数: 95 | 8 Suppose I have an object(molecular model) on a flat plane,
I now want roll it on the surface of cylinder, what is the
cartesian coordiantes of the model now? what if the surface
is the scroll, like the surface of a rolled paper?
I am a chemistry major, so the description may not be very clear.
Basically, what I want to do is, roll a crystal plane
to a cylinder or scroll surface. how to do this mathematically?
Thanks! |
|
t******7
发帖数: 4 | 9 本人刚接触高等代数，不是太懂，这儿暂借一下宝地，请教一下。
ring翻译为环，窃以为很不妥当，ring的定义为A ring is a set R equipped with
two binary operations + : R × R → R and · : R × R → R (where × denotes
the Cartesian product), called addition and multiplication.(wikipedia)，这
ring明明就是一个特殊的集合（set）嘛，跟我们所理解的 环 完全不是一个意思，环
让人想起几何形状。
代数中的ring的意思可能是这样的：a group of people who illegally control a
business or criminal activity.（Longman dictionary）
照此,ring其实可以译为"帮""组"什么的.
还有"ideal"的翻译，说是理想(子环)，环这个概念已经让人晕头了，再加理想二字，
更让人摸不着头脑。ideal指：an ideal is a special |
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U**R
发帖数: 5 | 10 First of all, happy new year to everyone!
I'm stumbled by a question that, I believe, ought to be easy...
Given two measure spaces (X, Bx, p) and (Y, By, q), each equipped with a
sigma-finite measure, p on the sigma-field Bx over X and q on the sigma-
field By over Y, respectively, we know that there exists a product measure
space (X*Y, Bx@By, p@q), where "*" denotes Cartesian product and "@" denotes
tensor product. Suppose, furthermore, that there are two other sigma-finite
measures, P on Bx ov |
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A****s
发帖数: 129 | 11 【 以下文字转载自 Quant 讨论区 】
发信人: Allens (ffff), 信区: Quant
标 题: a problem
发信站: BBS 未名空间站 (Mon Jan 18 21:16:40 2010, 美东)
Consider a cartesian product over n given finite sets,
X=X1×X2×。。。×Xn
Try to prove that X cannot be partitioned into less than 2^n subsets,
each of which is in form of Y1×Y2×。。。×Yn, Y1...Yn are proper subsets
of X1...Xn, respectively. |
|
o**a
发帖数: 86 | 12 【 以下文字转载自 Physics 讨论区 】
发信人: ouba (comfortably numb), 信区: Physics
标 题: a question on probability density
发信站: BBS 未名空间站 (Thu Feb 25 12:26:21 2010, 美东)
Folks, thanks for your time first!
function f = x.cos(a)**2 + y.cos(b)**2 + z.cos(c)**2
I know x > y > z. a, b, c are the angles between a vector and x, y, z axes
of a cartesian coordinate respectively.
If written in nutation and azimuthal angles,
f = x.sin(theta)**2.cos(phi)**2 + y.sin(theta)**2.sin(phi)**2 + z.cos(theta)
**2.
This vector is und |
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c****e
发帖数: 2097 | 13 This is called polar coordinate for a point, ie. the vector.
(for a body you'll need more angles to describe orientation)
basically, let the vector have length R, then its Cartesian
coordinates are given (in some convention) as
x_1=Rcos\theta_0
x_2=Rsin\theta_0(cos\theta_1)
x_3=Rsin\theta_0(sin\theta_1)cos(\theta_2)
....
and so on and so on. (realize that sum of the squares is R^2)
Then you can find inner products very easily. This is very
basic ^_* |
|
o**a
发帖数: 86 | 14 Folks, thanks for your time first!
function f = x.cos(a)**2 + y.cos(b)**2 + z.cos(c)**2
I know x > y > z. a, b, c are the angles between a vector and x, y, z axes
of a cartesian coordinate respectively.
If written in nutation and azimuthal angles,
f = x.sin(theta)**2.cos(phi)**2 + y.sin(theta)**2.sin(phi)**2 + z.cos(theta)
**2.
This vector is undergoing random re-orientation, i.e, the probability
density at (theta, phi) position is 1/(4pi)*sin(theta).
It is easy to see that z <= f <= x. Is th |
|
a****a
发帖数: 5763 | 15 "噢，那正是我要找的石头"
作者：杨振宁/刘兵 译
沃纳·海森堡（Werner Heisenberg）是历史上最伟大的物理学家之一。
当他作为一个年轻的研究者开始工作时，物理学界正处于一种非常混乱而且令人灰
心丧气的状态，对此，A·派斯曾用狄更斯在《双城记》中的话，将其描述为："这是希
望的春天，这是绝望的冬天"。
人们在做的是一场猜谜游戏：纯粹是通过直觉，一次又一次地，有人提出一些临时
方案，惊人地解释了光谱物理学中某些规则，这些了不起的成就会让人欢欣鼓舞。可是
进一步的工作总是揭示出新方案的自相矛盾或不完善，于是又带来了失望。在最后的光
明到来之前的那些年月中，这种司空见惯的起伏不定典型地反映在W·保利在1925年前
后四个月中写给R·克罗尼希的两封信中：
物理再一次走入了死胡同。至少对我来说，物理是太困难了。
海森堡的力学让我恢复了对生活的兴趣。
在第二封信中，保利提到的是海森堡在1925年夏天所做的工作。不过这一次与以前
那些充满欢欣与希望但又总是给人带来失望的时期不同，这是物理学中一个新时代的开
端。因为就在保利写这两封信之间的那段时间，海森堡独自在赫里戈兰渡假时，得到了
一... 阅读全帖 |
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x******i
发帖数: 3022 | 16 我一直是这么以为的：粒子运动产生磁场的时候用一次
叉乘，磁场对粒子产生作用的时候又用一次叉乘，两个
叉乘抵消，最后只有点乘，所以宇称守恒。
Cartesian
transforms |
|
b***k
发帖数: 2673 | 17 ☆─────────────────────────────────────☆
Allens (ffff) 于 (Mon Jan 18 21:16:40 2010, 美东) 提到:
Consider a cartesian product over n given finite sets,
X=X1×X2×。。。×Xn
Try to prove that X cannot be partitioned into less than 2^n subsets,
each of which is in form of Y1×Y2×。。。×Yn, Y1...Yn are proper subsets
of X1...Xn, respectively.
☆─────────────────────────────────────☆
netghost (Up to Isomorphism) 于 (Wed Jan 20 07:37:21 2010, 美东) 提到:
Let's say there is a particular subset with the form
Z1 X |
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t********s
发帖数: 54 | 18 Well, that's uniform in the polar coordinate sense, not in cartesian
coordinate sense. |
|
m*****n
发帖数: 2152 | 19 可以把polar转成cartesian啊，我也认为用polar更容易，更清晰。 |
|
l**n
发帖数: 67 | 20 We'd better keep a clear mind even we are facing numerous jargons
in physics and maths. A few comment on what we are talking
about in comso.8 could help.
Geometry analogy
Let's look at a point P on the flat plane in the 3-D Euclidean
space. And we just consider the local property of the P.
First we notice the distance relation is given by the familiar
law of Pythagoras,
ds^2 = dx^2 + dy^2 (1)
where x, y are our local Cartesian coordinates. Then we find we
can map the plane |
|
f*****w
发帖数: 16 | 21 Euclid(ean?)
and
Cartesian?
//bow |
|
l***s
发帖数: 7 | 22 因为这两个名字本来都不是英语啊. 象笛卡尔是从法语译的,
可是cartesian是按英文的标准来发音. |
|
N*********r
发帖数: 40 | 23 It solely depends on your distance measurement. If your measurement is
in a simple analytical form, e.g. Cartesian or Manhattan distance,
it's a well-defined (possibly non-linear) optimization problem, although the
solution may be non-trivial.
There are probably piles of papers discussing distance or distintiveness
of colors from human eye's prospective... I would say you could form a
reasonable distance measurement function candidate from any one of them :) |
|
m*****d
发帖数: 18 | 24 A.grad is Axdx+Aydy+Azdz in cartesian coordinate.
A curl B is A cross (curl B) |
|
r******n
发帖数: 54 | 25 Can you show some exapmle?
I doubt sql would be the best option.
Because it will do a cartesian product of two tables instead of matched
merge.
correct me if I am wrong.
thanks |
|
s*r
发帖数: 2757 | 26 可能是什么cartesian merge
都弄出500G来了 |
|
y******0
发帖数: 401 | 27 Something wrong with your code.Maybe it is cartesian merge.
Never merge two large datasets by many-to-many. I update a dataset by
merging 3 medical claims datasets (each about 20-50G) through one-to-many.
It take about 50 minutes. |
|
i******r
发帖数: 323 | 28 search SUGI(249_30) paper in google,just type merge and sql,very detailed
explanation. Hard to explain, but after reading paper you will be very clear
.
One major difference: sql doesn't need to sort the match-key, but merge
requires prior sorting.
Also different outcomes during Many-to-many merge, match-merge gives result
like one-to-one merge (n row), however, sql inner join is based on Cartesian
product, the outcome is n*n rows.
Also for large dataset, data step should be faster. |
|
s******y
发帖数: 352 | 29 what you can do is:
first create temp table which is a resultant set of cartesian join
color and size. then left join the temp table with your summary table.
create view temp as
select * from (select color from xxxx,select size from xxx);
select temp.* , cnt from temp
left join
(select color, size, count(*) as cnt group by color, size)
;
you have to verify the Mysql syntax. but the idea should be implemented
easily. |
|
s********p
发帖数: 637 | 30 Are you sure? no temporary datasets? Where is Cartesian Product stored? In memory?
temporary |
|
P****D
发帖数: 11146 | 31 Personal experience: once I wrote a buggy PROC SQL and created a huge
Cartesian product dataset, I got some sort of "out of memory" error - cannot
remember the exact words of the error message.
So I guess it's stored in memory.
memory? |
|
d*******o
发帖数: 493 | 32 俺觉得基本是个算法效率的问题。
做join的话，data step hash, data step array, Proc format都是key-value pair
（key--hash function--bucket structure)。三者的区别就是用的hash function不同
而已. Hash table的最大优点是数据量大的情况下，速度非常快。
Proc sql用的Cartesian product算法效率很低，但优点是兼容性好。所以也只有proc
sql能做up to 16 tables join和many-to-many join. |
|
s********p
发帖数: 637 | 33 肥猫，你笑死俺了
：所以也只有proc
你先说说many-to-many有啥用吧？做up to 16 tables join，谁会做那个？16个join,就算每个dataset 10个obs, Cartesian product 的obs都有10^16了吧
你能解释下为啥Hash table操作大dataset速度快么？
还有，俺问你个问题。如果有5个dataset，每个有10millions obs，1000个变量,只用data step和sql,哪种方法最快?
1)proc sql
2)sort+merge d1 d2 d3 d4 d5;
3)sort+
data d; merge d1 d2;
data d; merge d d3;
data d; merge d d4;
data d; merge d d5;
pair
proc |
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d*******o
发帖数: 493 | 34 新头像，新气象。谢谢捧场，哈哈。
"你能解释下为啥Hash table操作大dataset速度快么？"
这个像Microsoft, Amazon首轮面试题。像linked list， array，tree, hash table之
间的比较，我也不知道,答出来估计要看看数据结构的书了。
"up to 16 tables join和many-to-many join"
如果front end是relational database，多表join还是很有用的。
many-to-many join就更重要了。比如healthcare行业，一个人有多个claim，一个
claim table里可能有million个claim。只有Proc sql能做 many-to-many join。
"如果有5个dataset，每个有10millions obs，1000个变量,只用data step和sql,哪种
方法最快?"
个人觉得，其实merge大数据，不管哪种方法，最耗资源的一步是sort. 就像找CS的工
作面试肯定要问bubble sort/selection sort/quick sort... 阅读全帖 |
|
a*****3
发帖数: 601 | 35 传说中的 cartesian product? |
|
r******m
发帖数: 369 | 36 data step不能做cartesian join把，correct me if I were wrong.
用proc sql倒是可以 |
|
p***s
发帖数: 68 | 37 Note that Kirkland use MERGE without BY statement, it will not lead to a
Cartesian product. So it is OK. |
|
d******9
发帖数: 404 | 38 Question 2:
C is correct. 5 obs because SQL built a Cartesian product.
See the below SAS output.
data one;
input year $ qtr budget;
cards;
2001 3 500
2001 4 400
2002 1 700
;
run;
data two;
input year $ qtr sales;
cards;
2001 4 300
2001 2 200
2002 1 600
;
run;
proc sql;
select one.*, sales
from one, two
where one.year = two.year;
quit;
======================
The SAS System 23:32 Wednesday, April 1, 2009 1
year qtr budget sales
... 阅读全帖 |
|
A*******s
发帖数: 3942 | 39 more details?
i think 2 may be helpful coz "select distinct ID" actually performs a sort
on ID, but i am not sure how much a sort can help to optimize a Cartesian
join. |
|
d*******o
发帖数: 493 | 40 我猜1。Proc SQL的第一步是判断有没有equijoin，如果不是才会用step loop形成
Cartesian product。所以normalize database才这么重要。
可以看下面这个例子里面log的执行方案，2比1复杂的多。
data a b;
set sashelp.class;
rename name = id;
run;
proc sql _method;
select a.* from a, b
where a. id =b.id;
quit;
proc sql _method;
select a.* from a, b
where a.id in
(select distinct id from b);
quit; |
|
h********o
发帖数: 103 | 41 That's Cartesian product of tables:
========================================
DATA TEMP1;
DO DATE_N = 1 TO 31;
OUTPUT;
END;
RUN;
DATA TEMP2;
DO T = 1000 TO 2000;
OUTPUT;
END;
RUN;
PROC SQL;
CREATE TABLE TEMP AS
SELECT * FROM TEMP1, TEMP2;
QUIT; |
|
s*z
发帖数: 132 | 42 * cartesian product join of all rows;
proc sql;
create table test as
select a.x as x1,
a.y as y1,
a.z as z1,
b.x as x2,
b.y as y2,
b.z as z2,
case when a.x = b.x and a.y = b.y and a.z = b.z then
num + A
else num + B
end as num_new
from table1 as a, table2 as b
;
quit; |
|
a******n
发帖数: 11246 | 43 你可以看一下sas prep advanced，就在proc sql那几章。
关于cartesian product本身，可以wikipedia。 |
|
p***r
发帖数: 920 | 44 1.单就merge功能而言，区别在于many to many match
2.sql merge 相对容易，能理解
3.data step 可以在 merge 的同时做其他许多事情，比如，你要找出那些不 match 的
observation, 或者要进行很多的 format 和计算， data step 比较合适 raw data
processing and QA.
4.速度上，在SAS系统下没有太大区别，如果数据太大超过几个G,估计都干不了(我猜的
)。
记住最重要的一点，sql 是 Cartesian product, data step is PDV. |
|
n**********r
发帖数: 96 | 45 proc sql结构易懂，merge快，
proc sql只能合并出一个表，merge可合并产生出多个表
一对一，一对多，两者结果一样的,proc sql不用sort，merge要sort
多对多不一样:
当by变量只有相同值时，merge产生与第一个data set相同数量的obs,而proc sql产生
cartesian product.
当by变量有不同值时，merge产生最多的obs,proc sql只输出by的match的obs |
|
z**********i
发帖数: 12276 | 46 当我用PROC SQL时,发现,"THE EXECUTION OF THIS QUERY INVOLVES PERFORMING ONE
OR MORE CARTESIAN PRODUCT JOINS THAT CAN NOT BE OPTIMIZED."并且,很长时间也没
有完成.
请大家给点建议如何找到多个DATASET的不同,他们共同的VARIABLE是PROVNUM,并且,我
只要看这一个VARIABLE,其他的,不需要.
多谢!!
5 |
|
l****u
发帖数: 529 | 47 如果你想把B.agagroup换成A.agegroup，你就应在where statement 中在加上A.
agegroup=B.agegroup 就象where rate in (select rate
from b
where time<=100
group by B.agegroup
having time=max(time))
and a.agegroup=b.agegroup
因为如果不加这个条件，proc sql inner join 就会变成 Cartesian product join。
自然会影响你的结果。
|
|
k*z
发帖数: 4704 | 48 这个问题我们已经遇到过了，解决办法很简单，让DBA or ELT developer把你要的join
做成view放到数据库上去。如果经常用可以写store procedure，在SAS batch里call.
你需要做的是要在一个database里把join做好，也就是你要把Join做成一个view放到
database上去，否则你把两个tables在SAS里做join,SAS会把数据从SQL都带过来，然后
join，基本上就是你需要把所有的数据都带到服务器或者本地然后join,而不是在sql里
join好了，然后查询。
如果你的一个表在lib a, 一个表在lib b,那么就更糟糕了，sas会把数据都带到服务器
或者本机，做 Cartesian join,然后查询额。 |
|
v**********m
发帖数: 5516 | 49 Sir Karl Raimund Popper, CH FRS[1] FBA (28 July 1902 – 17 September 1994)
was an Austro-British[2] philosopher and a professor at the London School of
Economics.[3] He is regarded as one of the greatest philosophers of science
of the 20th century;[4][5] he also wrote extensively on social and
political philosophy.
Popper is known for his attempt to repudiate the classical observationalist
/ inductivist form of scientific method in favour of empirical falsification
. He is also known for his oppo... 阅读全帖 |
|
