Electric Field Inside of a Conductor

Question: I have seen many explanations for why the net electric field inside of a conductor is zero (assuming only electrical forces are acting on the particles inside of it). These explanations typically say that the charges in the conductor will move the outside and, to ensure that they remain stationary, there must be a net electric field of zero everywhere inside of the conductor. There seems to me to be a very large disconnect in this logic. If all of the charges are on the surface, then yes, I understand that the electric field near the surface of the conductor must be zero, but why does it have to be zero at, say, the center of the conductor (where there are presumably no charges).
Comment: Well why do you think there has to be a field where there aren't any charges?
Comment: I don't think there has to be, I am wondering why there can't be. A lot of facts about conductors are derived from the idea that the electric field is zero everywhere inside of a conductor. But why does this necessarily have to be the case?
Comment: Because if there was a field that never went to $0$ then there would be an indefinite net flow of charges
Answer: I think that part of the problem stems from the (somewhat misleading) sentence "The charges inside a conductor move to its surface.". That is true only of the excess charge inside the conductor.
Using an example to clarify things, if a conductor is composed of, say, 10000 protons and 15000 electrons, we can expect some 5000 electrons to migrate to the surface of the conductor. However, the remaining 20000 particles will stay inside the conductor. Now, these particles are still charged, and they are more or less free to move (in metals, it's mostly the electrons that can do so). Thus, if an electric field existed inside the conductor, the charges would quickly start moving around (even if, on average, the interior of the conductor remained neutral). That would generate a current, magnetic fields, and so on, contradicting the assumption that we are dealing with a static conductor.
So, if we insist on a static situation, we must also insist on the fact that inside the conductor the electric field must be zero. If there is an excess of charge in the conductor, the $\mathbf{E} = 0$ condition will be achieved by a "smart" distribution of this excess on the boundary.
Feynman's lectures 5 and 6 on electromagnetism (particularly sections 5.9, 5.10 and 6.6) offer some more insight into this subject.
Answer: Well it goes with the assumption that it's a charge distribution in equilibrium and there isn't any current. It's important to note that electric field is not zero in a conductor carrying current. But here we are assuming no current.
If there was an electric field in the center of a conductor then, unless the conductivity is zero, there will be some current resulting from the electric field, violating our assumptions. Current density and electric field are related by
$$\mathbf J = \sigma \mathbf E$$
If you allow non-equilibrium conditions then there is little restriction on where you can place the charges and what the resulting electric field inside the conductor will be. But the charges won't necessarily stay there.
Discussing the equilibrium conditions is a very useful constraint.
Comment: But what are the charge carriers of this current? If there is an electric field in the center of the conductor, but no charges there (because all of the charge is on the surface), what is moving?
Comment: It's possible to have a current carrying region with no net charge. This happens when the charge of the electrons is canceled by positive charge of the nuclei. There are charges in the interior of a solid but also positive nuclei. But we can still think of charges away from neutral as essentially a charge density on the surface. Bulk electric current flow for DC will happen in the interior of the wire. Here we must consider the electrons in the interior as charge carriers, but the electric field is still determined by the charges at the surface, even while carrying current.
Comment: @dts If there was electric field only at the center and not at some place nearby,with no charges at the centre,then it will be a direct violation of Gauss's law.

Electric Field Inside of a Conductor


After the nuclear option is invoked, are 51 votes required to move to cloture or just a majority provided quorum is met?

Question: I'm wondering if it's just a majority needed from those present (provided there are 51 senators present in total), or if it's a majority in terms of total senate seats (51)? Is this true even for the Supreme Court nominations?
Answer: Technically speaking, the filibuster is a dead letter rule. The nuclear option is invokable to change the rules any time the majority sees fit. Thus we have seen its use to limit the filibuster in

General judicial nominations and Presidential Cabinet positions (2013, Democrat majority)
Supreme Court nominations (2017, Republican majority)

There's no reason it cannot be invoked for general legislative matters.
To your question, the Senate Reference on Rules and Procedures state

Article I, section 5 of the Constitution requires that a quorum (51 senators) be present for the Senate to conduct business. Often, fewer than 51 senators are present on the floor, but the Senate presumes a quorum unless a roll call vote or quorum call suggests otherwise.

Since the majority does not need the opposition to establish a quorum, nor to pass the vote, you should not need any more than 51 Senators to consent to a nomination.
Comment: My apologies, as I wasn't clear. So with head count, 60 senators present, 31 yeas, and 29 nays, it would pass?
Comment: @RandomPleb Machavity is wrong. With 60 present it would pass. Majority vote is defined as more voting in favor than against. Quorum is defined as the majority of senators present in the room. So if 60 senators are present and the vote is allowed to happen, 31 senators is sufficient to pass the motion. However the other 29 senators can simply ask for a quorum call and leave the room. In that case there would be only 31 senators left and a lack of quorum. But if the 29 stay in the room(let's say they vote no), there is a quorum and the motion passes.
Comment: Additionally, if the vote is filibustered, then 60 senators must vote to approve cloture by the current rules (unless its a presidential nominee issue, then by https://www.senate.gov/CRSpubs/be873e40-a966-4feb-9d72-cf23a93cbe46.pdf majority is required, which in the case of 60 senators is 31. However once again the 29 senators who oppose the motion can just call for quorum and leave). The nuclear option only requires majority vote to invoke because it is done through a reinterpretation of the current rules (appeal of the decision of the chair), which 31 of 60 senators can invoke.
Comment: @Machavity in terms of the quorum citation I would point you to the Wikipedia article https://en.m.wikipedia.org/wiki/Quorum which makes it clear that quorum is the number of people needed to conduct business, not the number of people who have to vote for a certain motion. If you would like I can probably find a CRS report on quorum to shed further light on this issue.
Comment: Note that any Senator at any time can call a quorum call.  That question to the Chair must always be considered in order.
Comment: So to be clear: let's say 60 senators are present, would the nomination still pass with a mere 31 votes?
Comment: @RandomPleb No. You still need 51 votes (or a majority of ALL votes) for it to pass. You could have a 50-10 split and have the VP cast a tie breaker, but that's the only other scenario there.
Comment: @RandomPleb There's one other scenario here. Let's say there's only 45 members present. As long as nobody calls for a head count, you could pass things with a simple majority there (so 23-22), but on contentious things there's certain to be a head count to establish a quorum.
Comment: @RandomPleb No. The nays would certainly demand a roll call to determine a quorum. At this point **the threshold is always 51 or more**. In other words, only if everyone agrees to suspend the rules can less than that carry the day.
Comment: @Viktor Got a citation for that? Am more than happy to admit I'm wrong but just saying so doesn't make it so.
Comment: @Victor is correct.  You can look at senate voting records to see that bills and motions often pass with fewer than 50 votes, when there are 98 or fewer votes cast.  Cloture is unusual in that the threshold is defined as 3/5 of the number of seated senators (i.e., absent senators count in the denominator but vacant seats do not).  Formerly, the threshold was 2/3 of senators voting.  If the threshold were formally lowered to a majority, it could use either number in the denominator or indeed the whole number of seats whether filled or unfilled.
Answer: First some background: approval of Presidential nominees (or any other matter) always required only simple majority vote. The trick was that the Senate rules required three-fifths of all Senators to affirmatively vote to end debate. Thus if any Senator were to filibuster a nominee, 60 Senators (and no less assuming that all Senators are chosen and sworn) to end a filibuster. In that case less than 60 Senators could never end debate and thus a filibuster with enough support would defeat a nomination.
According to https://www.senate.gov/CRSpubs/be873e40-a966-4feb-9d72-cf23a93cbe46.pdf only majority vote is required to invoke cloture on all nominees except for Supreme Court Nominees (Until April 2017). I wanted to check the record to confirm and further supplement this answer.
According to page 5 and 6 of the Senate Congressional Record on November 21, 2013 (see https://www.congress.gov/crec/2013/11/21/CREC-2013-11-21-senate.pdf, pages referenced numbered S8417 and S8418), Senate Majority Leader Reid made a point of order that the cloture motion requires a majority vote. The President Pro Tempore (acting as the Chair of the Senate) ruled that this point of order is not sustained. In response, Senator Reid appealed the decision of the chair. The appeal was carried.
Afterwards, Senate Minority Leader McConnell, made a point of order that the appeal required 2/3rds vote and not majority as it effectively changed the rules of the Senate. The chair indicated that his point of order was not sustained and Senator McConnell in turn appealed that ruling. It was not carried.
Thus the rules of the Senate as of November 21, 2013 indicate that three-fifths of the currently chosen and sworn are required to invoke cloture. However, the rules have been interpreted (funny things happen when the politicians who write the rules also need to interpret them) to only require majority vote to invoke cloture on all Presidential nominees except for Supreme Court nominees.
Now this was precedent of the Senate until April 6, 2017. On that day a motion to invoke cloture on a Supreme Court nomination was not carried (55-45 for those interested). After the motion to invoke cloture did not carry, Senate Majority Leader McConnell asked to reconsider the vote and as reconsideration requires only majority, this carried by a vote of 55-45. Afterwards, Senator McConnell made a point of order that in fact the 2013 appeal covered all nominees, including Supreme Court nominations (note: it explicitly did not). The chair did not sustain this point and Senator McConnell appealed the decision of the chair. The appeal was carried by a vote of 52-48, (see pgs 7-8 here: https://www.congress.gov/crec/2017/04/04/CREC-2017-04-04-bk3.pdf S2390 is the exact numbering on the page).
As of this date all executive nominations require majority vote to invoke cloture. Note the appeals never indicated that cloture need be invoked by absolute majority, only simple majority. As a result, if the Senate has quorum, it only takes majority vote to invoke cloture (assuming all other prerequisites to invoke cloture are met). Quorum is defined as majority of the Senators. Thus at least 51 Senators need to be present (which essentially means whenever you see a vote of 51-50, ie. when the Vice-President votes, the senators on the losing side could have taken the path of simply leaving the Senate without quorum, as the Vice-President does not count for quorum).
Assuming that at least 51 Senators are present and stay in the room and if more than half vote to invoke cloture (or without filibuster, unanimously agree to proceed to vote), then once again only majority is now required to approve the nomination. Thus 51 or more Senators present in the room is sufficient for the majority to confirm a nominee and overcome a filibuster.
Seeing as many Senators are eager to win re-election they are eager to put themselves on the record as supporting or opposing the President. As such this situation where less than an absolute majority approve a nominees is unlikely to occur.
In regards to other matters, the rule on cloture has not been "interpreted" in any unusual way for matters other than nominations. Thus since the nuclear option has not been invoked for those matters, three-fifths vote is still required to invoke cloture on those matters. However, without objection a simple majority of those present can approve things like laws and resolutions. The nuclear option can of course always be invoked on these matters and invoking the nuclear option only requires simple majority vote. Once that is done a simple majority vote can end debate and then proceed to a vote and once that is done, a simple majority vote on the actual matter carries the matter.
Comment: "senators on the losing side could have taken the path of simply leaving the Senate without quorum": quorum is presumed unless a senator raises a point of order.  So you need at least one minority member present to do that, which means you can't prevent the majority from acting unilaterally unless there are 49 or fewer members of the majority present.
Comment: phoog, you raise a very valid procedure point. Procedurally it is difficult for the minority to force the absence of quorum once it has been established. However, if it becomes clear that the majority plans on taking this path, all the minority needs to do is force the absence of quorum once the Senate is in a pro forma session or some other session of the Senate. It is very likely you will be able to find a time prior to the vote when all 50 other senators will not be there. Then, simply, the minority can leave (or even catch an int flight) and the Senate will not be able to establish quorum.


how can I get maximum bandwidth of an interface in linux C?

Question: Let's say I have a machine with 3 NICs; wifi, eth, and 3G. I'm trying to get the ESTIMATED speed (or bandwidth) at which a link CAN transmit at a given time for each of these interfaces and determine which one is the fastest. Again at a given time. I'm writing a linux kernel module. I'm using kernel version 2.6.35. Is there anyway to measure the available bandwidth? Even if it meant sending a testing ping to measure something like we do in measuring latency ...
Answer: iperf can help you measure actual bandwidth
http://sourceforge.net/projects/iperf/
Answer: Actually, this is a difficult problem.  If you know all three NICs connect to a common site, the obvious straightforward test is to transfer some data through each NIC and time them.
However, given the difficulty of the problem in general, it might be "good enough" to broadcast UDP through each NIC and time that.  That fails to reveal any receive performance, but it is better than nothing.
Answer: At Linux, you should read /proc/net/dev (you have the total packages/bytes sent. Get these numbers at your 'start' and 'end' time)
http://linuxdevcenter.com/pub/a/linux/2000/11/16/LinuxAdmin.html
http://www.linuxjournal.com/article/8381
(Source here: How can I get the current network interface throughput statistics on Linux/UNIX?)


Confused about 民国 dates on receipts

Question: I have been in Taiwan for about two weeks.  Some of my shopping receipts have 民国 dates, some have Gregorian, and some have both. What I find confusing is that when there is both, the day is not always the same on both. And I have at least two receipts with the same 民国 date but the Gregorian dates differ by two or more days.
Answer: 民国 (Republic of China) era starts from 1912. Therefore, just add 1911 to the 民国 year number and you'll know the Gregorian year number. For example, 民国106年(ROC Year 106)=1911+106=2017 A.D.
Sometimes, 民国 is omitted for simplicity. To distinguish ROC year from Gregorian year, follow this rule:
If a year number is relatively small (no matter whether it's larger than 100), it's an ROC year number. (Therefore, 98年 (Year 98) is not Year 1998, it's Year 2009).
The above rule only applies to daily life, not for academic use. However, the date of the year should remain the same on both ROC date system and Gregorian date system. If you see differences, it must be produced by "magic" reasons rather than different date systems.
Comment: I repeat: the DAY was different.  However, I think I figured it out.
Comment: I have updated the answer. I have noticed that you say the day was different.
Comment: And I edited the question to make it plainer.
Answer: I think I have figured it out.  What I thought was the day in the 民国 date was not the day.  The ones with the apparent discrepancy were showing the 民国 months of a lottery system.  I did not know about the lottery at the time, so when I saw three numbers, I interpreted them as year, month, day.  But actually, it was year and two different months:
107年01-02月
The numbers were more prominent than the 汉字 and so I thought I was seeing the second day of the first month, when it actually refers to the lottery cycle of the first and second months.
Comment: Easy way to tell is Asian dates are given in Y M D, so the number in the middle wouldn't be date.
Comment: The number in the middle, as I said, _wasn't_ in the middle.  It was _two_ months at the end.  A _range_ of months in a format the looked like month-day.
Comment: *I know* what it is. And no, the format doesn't look remotely like "month-day", because the last number is followed by the word "month". I'm pointing out that since the last number is clearly marked as the month, and we know from the Y/M/D format that the middle number can't be the day, it's intuitive to conclude that it's a range of months - as is obvious.
Comment: I repeat: because the numbers were made much more prominent than the hanzi, it made me think of 107-01-02.  You can say "doesn't look remotely like," but obviously it wasn't remote enough for me, or this question would never have been asked.
Comment: I fully understand that you were mistaken, there's no need to keep repeating the obvious. But again, a number followed by the character "month" means... month, not day. You can either accept this simple, intuitive rule for the future, or keep being defensive about getting it wrong, it's no skin off my back either way.

Confused about 民国 dates on receipts


Can a mixed boundary conditions in 1D Linear FE lead to non positive definite stiffness?

Question: Consider the finite element discretisation of a  general second order linear differential equation, with mixed boundary conditions at the end. The boundary conditions are given as $\alpha_0u'(0)+\beta_0u(0)=\gamma_0$ and $\alpha_1u'(1)+\beta_1u(1)=\gamma_1$. Where $u$ is the dependent variable and the domain is $(0,1)$. The reduced stiffness matrix after applying the boundary conditions also depends on the coefficients of the mixed boundary conditions: $K_{11} \rightarrow K_{11}(\alpha_0,\beta_0)$ and $K_{nn} \rightarrow K_{nn}(\alpha_1,\beta_1)$.
Since $\alpha_i,\beta_i$ are arbitrary, can it so happen that for some values of these, the stiffness matrix is NOT positive definite?
Comment: as far as I remember the Robin (and Neumann) BC's increase the diagonal value, discretize your BC and make use of it's value $K_{n,n+1}=f(K_{nn})$, where $f(K_{nn})$ is some function of the value inside your domain. So the matrix should remain pos def if it initially was.
Answer: Let's combine your $\alpha,\beta,\gamma$ into fewer symbols by diving your boundary conditions by $\alpha$.
For the general-dimensional case,
$$
  -\Delta u = f, \qquad \text{in $\Omega$}, \\
  \frac{\partial u}{\partial n} = \alpha u + g, \qquad \text{on $\partial\Omega$}, \\
$$
the weak form you get after multiplying by a test function $v$, integrating over the domain integrating by parts, and using the boundary condition is
$$
  a(u,v) = \int_\Omega \nabla u \cdot \nabla v - \int_{\partial \Omega}\alpha u v.
$$
This form is for sure positive definite if $\alpha<0$. It is also positive definite if $\alpha$ is less than the Poincare constant on the domain, but if you make $\alpha$ large enough, then the whole thing becomes indefinite, and consequently your system matrix may also not be positive definite any more (even though it is symmetric).
Fortunately, physically correct models will always lead to cases where $\alpha<0$. For example, for the heat equation, $\frac{\partial u}{\partial n}$ is the outward heat flux from the object to a reservoir of temperature zero (assuming $g=0$), and for positive interior temperatures that means that there must be a positive outward heat flux -- that is, $\alpha<0$.
Comment: @aaquib This depends on your solver. For symmetric consistent positive semi-definite systems you can use conjugate gradients, for consistent symmetric indefinite systems you can use SYMMLQ, for symmetric indefinite inconsistent systems you can use MINRES, for non-symmetric consistent systems you can use BiCGStab, CGNE, for non-symmetric inconsistent systems you can use CGNR, LSQR. Inconsistent systems suggest that you wrote a PDE that has no solution (e.g. you specified contradictory boundary conditions), so that may be a mistake, however CGNR will find  the projection with minimum norm.
Comment: Thank you. If I have a random differential equation which has a non PD stiffness, will the FEM still converge to the correct result?
Comment: @aaquib There are of course many differential equations that, regardless of the boundary conditions, lead to indefinite linear systems. For many of these, the finite element method still works, but as lightxbulb states, you will need to use a different linear solver because Conjugate Gradients will no longer work for such systems.
Answer: You are right, positive definiteness is NOT always true. I checked it again for a simple case.
As a simple example, consider a 1-dimensional Laplace equation for the region $0\leq x \leq 1$:
\begin{equation*}
\frac{\partial^2 u(x)}{\partial x^2}=0.
\end{equation*}
The Robin-like boundary conditions at $x=0$ and $x=1$ are specified in the question.
The starting weighted form is as follows,
\begin{equation*}
\int_0^1\delta u(x)\frac{\partial^2 u(x)}{\partial x^2}dx=0,
\end{equation*}
where $\delta u(x)$ is the arbitrary weighted function.
As always, after the application of partial integration, we have the weak form:
\begin{equation*}
-\int_0^1\frac{\partial \delta u(x)}{\partial x}\frac{\partial u(x)}{\partial x}dx
+\left.\delta u(x)\frac{\partial u(x)}{\partial x}\right|_{x=1}
-\left.\delta u(x)\frac{\partial u(x)}{\partial x}\right|_{x=0}
=0,
\end{equation*}
whch is rewritten as,
\begin{equation*}
-\int_0^1\frac{\partial \delta u(x)}{\partial x}\frac{\partial u(x)}{\partial x}dx
+\delta u(1)u'(1)-\delta u(0)u'(0)=0.
\end{equation*}
Substitution of Robin-like B.C given in the question yields:
\begin{equation*}
\int_0^1\frac{\partial \delta u(x)}{\partial x}\frac{\partial u(x)}{\partial x}dx
+\delta u(0)\frac{1}{\alpha_0}(-\beta_0u(0)+\gamma_0)-\delta u(1)\frac{1}{\alpha_1}(-\beta_1u(1)+\gamma_1)=0.
\end{equation*}
If one divide $[0,1]$ region into $(n-1)$-finite elements, we get,
\begin{align*}
K_{11}\rightarrow K_{11}(\alpha_0,\beta_0)&=K_{11}+\frac{1}{\alpha_0}(-\beta_0), \\
K_{nn}\rightarrow K_{nn}(\alpha_1,\beta_1)&=K_{nn}-\frac{1}{\alpha_1}(-\beta_1), \\
K_{\text{others}}&\rightarrow\text{unchanged}.
\end{align*}
Thus the positive definiteness of K-matrix is NOT true under some boundary conditions.
Comment: You should probably elaborate on how you reach the conclusion that $K$ is not positive definite from the above (e.g. trace being equal to the sum of the eigenvalues, and the eigenvalues of a positive definite matrix being positive).
Comment: @lightxbulb Is it because you can always choose $\beta_0$ large enough?
Comment: @aaquib You can make $-\beta_0/\alpha_0$ or/and $\beta_1/\alpha_1$ negative and large enough by absolute value to get $K_{11}$ or/and $K_{nn}$ negative. For positive definite matrices the diagonal elements have to be positive, so $K_{ii}<0$ would contradict this.
Comment: Do each of the diagonal elements have to be positive? I thought it was the trace that mattered. Anyhow, does this affect in any way to convergence/stability of Robin BVPs? Because the only other non-positive definite problem I know is of buckling instability
Comment: @aaquib if any diagonal $K_{ii}$ is negative, then choose the vector $v$ with $v_i=1$ and all other entries 0, then $v^\top K v = K_{ii} < 0$ so $K$ is not PD.


How do I save software on a 3DS transfer?

Question: So I've recently bought a New 3DS XL to replace my old 2DS, and the 3DS has a copy of Super Mario World pre-installed on it. When I do a system transfer, is there any way to save the game??
Comment: Is the New 3DS XL that you purchased the Lime Green one? Because if so, when you do the system transfer, it should keep the game.
Answer: After posting my speculative comment, I did a little bit of research and found this article by Nintendo about the pre-installed software for the 3DS.

Pre-installed games are stored on the SDHC Card or microSDHC Card included with the system. This means that a portion of the available space will be taken up by the pre-installed game. If you choose to delete the content off the SDHC Card or microSDHC card, such as during a system transfer, the pre-installed game will be available for redownload from the target system's Nintendo eShop after the transfer has been completed.

(Emphasis mine.)


How can I find accurate start and stop dates for my resume from jobs that I had 20 to 35 years ago?

Question: I have been working in the same type of job for over 35 years. In putting my resume together I no longer remember the exact start and stop dates for jobs from several years ago.  How do I get these dates accurate without having to call all of my prior employers?
Comment: And remember -- if *you* can't find out the exact detailed dates, then *they* can't find out either.
Comment: usually firms only care about the last 10 years. that should be correct. Before that noone cares or verifies. Infact i have compressed 10 years on my resume to a single line . e.g Apr 1990- Apr 2000 - Various Clients. Software Developer/Analyst. Worked as a software developer at various financial clients.
Comment: @A.I.Breveleri Not necessarily true (you may not be able to afford a background check, but the company could).
Answer: You don't.  Unless you're applying for a job with some sort of extremely high security clearance - no interviewer, hiring manager, or HR person is going to care.
In my (considerably) shorter CV, I say:

June 2012 - January 2014 - Head of Widgets at Foo Corp
August 2010 - May 2012 - Widget Builder at Bar Corp
2008 - 2010 - Widget tester at Blah Corp

Remember, the person hiring you is looking for evidence of your skills, what you're like to work with, how you approach problem solving.
If you have a form that specifically asks for the exact date - I think it's perfectly acceptable to put the first of the month if you don't know.
Comment: Exactly.  The further back in time, the less accuracy is required.
Comment: How much you want to bet that not even your previous employer will know?  Just ask your old managers...  this is information that you can't even obtain even if you tried, and the cost far outweighs benefits (most of the time there are zero benefits).
Comment: my old Boss for whom i worked in a Restaurant thought I was the handyman. I was the cook/waiter :D
Comment: Indeed.  And to be honest, the few I totally forgot... I estimate.
Comment: This.  It's a matter of "accurate enough" - and for ancient history, you don't need that level of accuracy.  They just need the gist of it.
Answer: Ideally, you'd locate an old copy of your resume which would have the information on it.  Did you ever post a resume online?  Perhaps you could search for it.
Failing that, what other records do you have from that time?  Do you have any copies of old tax filings?  Photos from a farewell party your co-workers might have thrown for you? Go through your old filing cabinets and see what you can find that would help you pin things down.
Are any of your job start or end dates anchored about other life events, like moving, buying a house, or the birth of a child, that you could use to reconstruct dates?
If you really can't find accurate dates, I think it's fine to put "approximately" next to the dates in your resume for those jobs whose dates you cannot pin to a specific month and year.
Comment: As a hiring manager and as someone who uses approximate dates for positions held in the far path, I agree that "approximately" works just fine.  More than a few years back, or when the jobs are held for more than a few years themselves, I don't particularly care what month or day they started or stopped.  I care about gaps, sure, but at some point the particulars just stop mattering.
Answer: This isn't quite what you're asking, I know, but I would recommend not putting all 35 years of your experience on your resume. The last 10-15 years, absolutely. The problem with putting 35 years or even 20 on it is that you're basically opening yourself up to be denied jobs based on your age. It's technically illegal but all a prospective employer has to do is look at the years on your resume, do the math, and figure out that you are at the least in your mid-50s (assuming you didn't enter into the industry when you were 7 or something). From there they can drop your resume into the circular file if they're so inclined and you'll never know the difference.
This article on CareerBuilder.com backs up what I wrote and also provides possible exceptions (for instance, if the job you're applying for is specifically looking for people with decades of experience):
http://www.careerbuilder.com/article/cb-2169-resumes-cover-letters-your-work-history-how-far-back-should-you-go-on-a-r%C3%A9sum%C3%A9/
This article from CBS News uses the same rule of thumb (~10 years):
http://www.cbsnews.com/news/how-far-back-should-your-resume-go/
Comment: What about the date of birth? In Switzerland, we need to add that to the resume. No hiding.
Comment: Strongly agree. I saw this first hand after I turned 40 when suddenly the resume that got me frequently interviews stopped working so well. Cut those old jobs off and interest went right back up.
Comment: You make a valid point, but I am afraid removing older jobs helps very little, because the year of graduation still gives enough clue as to the candidate's age, in most cases. That said though, I am not sure there is any better solution. Sadly enough, even if you do get an interview, your face still reveals your age, so they could still reject you despite being fully qualified.
Comment: @malach: I just wanted to post the same thing. This answer is quite US-centric, in many places (Switzerland, for example) your date of birth is a standard thing that goes onto your CV.
Comment: @MaskedMan While it is true that an employer absolutely determined to discriminate against older candidates can do so after an interview, most aren't that determined. And the deeper one gets in the process, the harder it is to get away with. On my resume, I don't include the graduation year of my bachelor's degree. This hasn't hurt me yet. (Canada)
Answer: This is kind of screwy, but you could always run a background check on yourself. (This is assuming that you're in the US.)
But here's some other information, from friends who work in HR: companies don't care too much if dates are within two or three months of being accurate, and really far back they won't care much if the dates are a little outside that range. You can give the explanation that you don't have an exact month, but you can give the exact year, and season (winter vs. summer) which will nicely fall within six months of being accurate, at worst. Most (95%+) employers are going to be good with that.
Answer: From what I saw, companies rarely care about jobs that you had more than 10 - 15 years ago.
I wouldn't even bother putting those jobs there, you probably could make better use of the limited space of a CV to put more relevant stuff in there. I don't know in what industry you work in, so I don't know exactly what "more relevant stuff" could mean in your case.

If you do decide to put that information in there, maybe you could find it in:

your old contracts you had with those companies. I doubt someone keeps them for so long, but maybe you can still find them in a dusty box in the garage
some emails you exchanged with your employer during that time and you still have the account or you copied them to a newer account

If you really can't find this information, then don't worry too much about it. Just put down only the years, if you remember them. Like "1979 - 1983" or something similar. Trust me, given the length of time since then, it won't really matter (a lot of your coworkers and bosses are already probably dead).
Answer: To echo some of the other answers, the further back you go, the less someone cares.  It may be perfectly acceptable to estimate to the best of your knowledge, but this could depend on the individual company and may not be acceptable to all.
True story from my own experience... I applied to a company I had interned with 13 years prior (a Fortune 500 company with very strict hiring processes), and I actually had the wrong dates for the internship on my resume. I had the months correct, but I was off by an entire year. I repeated that error in my background check as well. And no one even questioned it or asked, and I was hired without issue.
In fact, I didn't even realize the mistake until I applied for an internal position 2 years later when the internal application pre-populates your internal positions.
So you should try to be as accurate as you can, but when you get past the last 10 years, it becomes less important to be 100% correct. They hiring manager is more concerned with your experience.
Answer: In my country, Canada, we have these forms that get sent to the Employment Office called Records of Employment. These are affiliated with my SIN number and every time I leave or stop a job, a record of employment is sent in triplicate with one copy to me, one my employer has to keep for 7 years and another that the government Employment Office gets. Does your country have a similar setup? If so, there might be a solution of asking your Employment Office to repeat back you the start and stop dates (these are always listed on the form).


Algorithm(s) for finding moving entities in a maze

Question: A have a maze and character that's controlled by the player and a drone who has to find him (by itself). Does anyone know an (efficient) AI algorithm for doing something like this?
P.S. I know there are several path finding algorithms(e.g. A*), but as far as I know these only work for finding the path between two nodes that "don't move" (this would work if my character was standing still, but that's obviously not the case).
Comment: Does the drone know the maze layout or does it have to discover it as it goes? Also, does it know where the player is within the maze as it moves?
Comment: A* also requires that you know beforehand the locations of the start and end points. Does the drone know where the player is and just has to reach it? Our does the drone also need to locate the player?
Comment: @cdeszaq Yes, it knows the layout of the maze (although I wouldn't mind an algorithm the assumes it doesn't know it) and yes, it does know where the player is within the maze.
Comment: @JackEdmonds Yes, it just has to reach him. But take into account the fact that the player is constantly moving.
Comment: If the maze is not too big you could use Floyd-Warshall to get all shortest paths. Then you can lookup the shortest path for all possible player <-> drone positions. If your maze is too big try to search the shortest paths between road junctions. Then you can lookup the shortest path for all possible player(next junction) <-> drone(next junction) positions.
Comment: @Zeta Its dimensions differ from run to run. But Floyd-Warshall isn't such a bad idea.
Answer: If the "start point" is where the drone is, and the "end point" is to run into the player, about the best you can do using just a "standard" algorithm is to use A* periodically and from that determine where the drone needs to move.
As you get closer to the player, you will be calculating faster and faster since the search space is, in theory, smaller.
Using this, it would be possible for the player to find a set of positions that, when moving between them causes the drone to get "stuck" just moving back and forth, but those sorts of optimizations are situation-specific and a general algorithm won't include them.
Essentially, you do have a fixed search space each "frame", but you just have to run it each frame to decide what to do.
There are likely tweaks to A* that cover minor perturbations between runs, but I don't know any off the top of my head.
Comment: I agree, A* is likely your best bet. You'll want the ability to stop A* in the middle of a calculation when the human has moved. You'll also need to update the start and end goals every time the human or drone have moved.

I guess you could also use something like Johnson's algoritm to find all shortest paths between all possible position's and then use it as a lookup table. That should work if the maze is not dynamic.

http://en.wikipedia.org/wiki/Johnson%27s_algorithm
Comment: The more I think about it. You are better off from a efficiency standpoint just to use plain old Dijkstra's algorithm from every vertex at initialization and use that as your look-up table. Like Johnson's algorithm, without the initial Bellman-Ford step since you cannot have negative weights in your graph. Essentially, all your weights should be 1.
Comment: This was actually the first thing I though of. One of the problems with this solution is that calculating the path might take the drone a lot of time and then its motion might look something like this: move a bit, then halt and calculate, then move again, then calculate again etc. I would like it to move constantly (kind of like the way the ghosts move in pacman).
Comment: @Justin - I like the idea of the lookup..._Much_ faster than continuously doing A*. You could use the same memoized idea _with_ A* and cache the results. Then you would slowly build the lookup table based on where the player and drone are and have been, ignoring the "un-visited" parts of the maze until they are needed.
Comment: @Justin Indeed, this solution sound better. I think I'll try this if I don't find something better.


Finding a solution for a PDE

Question: I am trying to solve the following PDE
$$\bigg(p \cdot \frac{\partial}{\partial p}+q \cdot \frac{\partial}{\partial q} +3\bigg)F_{1}(p,q)=F_{0}(p,q)$$
where $F_{1}$ and $F_{0}$ are two functions of $\vec{p}$, $\vec{q}$ and the operator on the left of the PDE involves the scalar products between a vector and the corresponding gradient. The right part of the equation is known to be
$$F_{0}(p,q)=\frac{\pi^3}{p^2q^2(p-q)^2}$$
where the squares denotes the scalar product of a vector with itself.
Given these conditions, what can be said about a generic solution of $F_{1}$?
Answer: It is a quasilinear equation we can apply the Lagrange method. Since $pF_p+qF_q=F_0-3F$, we have
$\frac{dp}{p}=\frac{dq}{q}=\frac{dF}{F_0-3F}$.
We can find its first integrals by solving these equalities. From the first two equaality (it is an ODE for $p$ and $q$) we immediateyl find that $p-q=c_1$, or $p=q+c_1$. Now taking the second and third equality and considering $p=q+c_1$, we get another ODE (for $q$ and $F$)
$(\frac{\pi^3}{q^2(q+c_1)^2c_1^2}-3F)dq-qdF=0$
with an integrating factor $q.$ After multiplying the eqution by this factor we get an exact differential equation: Solving this you'll get a second integral with arbitrary constant $c_2$. I think you can proceed from here. Your solution will be an implicit one either in the form $c_1=g(c_2)$ or $G(c_1,c_2)=0$ for arbitrary continuously differentiable function $g$ or $G$. Here $F=F_1$

Finding a solution for a PDE


Are the Leonid meteor storms a thing of the past?

Question: According to the Wikipedia article on the Leonids, "a close encounter with Jupiter is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many decades". Does this mean there will not be another incidence of the famous storms which spawned thousands or tens of thousands of meteors per hour within our lifetimes? Or will the 33 year periodicity reestablish itself?
Answer: Wikipedia does not cite a source.
NASA used to make predictions, eg.:

2009 LEONID OUTBURST FORECAST A significant shower is expected this year when Earth crosses the 1466-dust and 1533-dust ejecta of comet 55P/Tempel-Tuttle. According to J. Vaubaillon, the narrow (about 1-hr) shower is expected to peak on November 17, 2009, at 21:43 (1466) and 21:50 (1533) UT, perhaps 0.5 to 1.0 hour later

These are extensively studied studied, eg. List of all meteor showers  .
The great storms occur at ~33 year intervals. I can't find any prediction that this pattern will be unusually perturbed by Jupiter at this time.


How quickly are the funds from a bank deposit available via my debit card or a check?

Question: I deposited a cashier's check into my account at 8AM, the account had nearly nothing in it. If I were to use the "credit" option on my debit card at the grocery store would I overdraw my account? Do the "credit" transactions on my debit card go through immediately? If I were to write a check instead, and they didn't cash the check today, would I be safe?
Comment: What country are you in? Strangely enough, different countries have different banking systems, so an answer that applies to one country won't necessarily work for you.
Comment: What country are you in? Your bank should easily be able to tell you their rules for clearing checks. Have you asked them?
Comment: I am in the United States. From what I know about Cashier's checks, though, they are basically cash(from my understanding), and would act as such. The clerk at the bank told me that it did not act differently than a check, but I was skeptical.

Cash would be available immediately, from my understanding, and cashier's checks are the same as cash, so should be available immediately?

If not available immediately, and available the next day, would my checks work the same way then? If I were to write a check today, it shouldn't go through til tomorrow when the cashier's is available, right?
Comment: I have two accounts at the same bank (in USA). One has been active for 20 years, and the other is a year old. Funds are available to me 'same day' as deposit in the first account, and they generally take a week in the second. The first account has a long-term record that's trusted by the bank, so they treat it well. 'Same day' generally means "after 3 PM if deposited early, otherwise next day".
Answer: The bank will know best. You could look for their documents on the website that discuss funds availability. The size of the check could also make a difference.
One way to see if you can use the money is to look online at your balance. My credit union reports two numbers for each account: Balance and available balance. The difference covers the deposits that are in limbo, and the checks/withdraws that are in in progress.
There does not seem to be a relationship between credit/debt status with the debit card and the speed of the withdrawal. I have seen it take seconds, and I have seen it take days. It depends on the vendor.
regarding the use of a check. If you were mailing the check you would probably be OK, because of the time it would take them to receive it and process it. But handing the check to the store might not be any different than using a debit card. Many stores are now scanning the check into the system, then handing you back the paper check. that can be deducted within minutes of handing them the check.
While it seems that the cashiers check is as good as cash, there have been scams using cashiers checks. Your bank may not treat it as good until there has been time for the other bank to verify it.
Answer: Generally, checks that are deposited, are being put on-hold for a couple of days (or more, depending on the amounts) until the amount is available. But they do post on the date deposited, and usually some initial amount ($200 in my bank) is available right away. The amounts and holding periods change from bank to bank, so ask your bank. Usually, when you check balances online, it would show the amount available. If the check you wrote gets to the bank before the full amount is available it may bounce.
Cashier checks are not exactly like cash. Since there has been a lot of fraudulent activities involving cashier checks, many banks treat them as regular checks for most parts, including holding periods.
Comment: Note also if the cashier's check clears in, say, three days and is subsequently found to be fraudulent, you will be on the hook for it, even if you've already spent the money or sent it elsewhere. Common scams work by having you send back 90% of the cashier's check, which later turns out to be fraudulent.
Comment: Thanks for the answer. The fraudulent activities remark you made makes a lot of sense to why a cashier's check can't be processed as cash.


Is there any init function in sharepoint hosted app, It should run once when app is installing

Question: I have to create list when SharePoint hosted app is installing. Is there any function call in SharePoint which runs when app is adding or installing in SharePoint site.
Comment: May be not!!! In provider hosted app, there is. Can you explain why you need that.
Comment: I have to write code to create lists when app is installing/adding to SharePoint site. I have 3 to 4 app parts in my app. Now I have write code to create lists in site where app is installed, where I have to add my code to create lists
Answer: If you just need to create a list, you can do it using CAML. The SharePoint-Hosted App contains a sandbox solution. When the App is installed the Feature in the sandbox solution is activated and the list will be created.
The ability to do this through code is not built-in without using a Remote Event Receiver. But, if you use a Remote Event Receiver, you are no longer building just a SharePoint-Hosted App. You are also building a Provider-Hosted App.
It's not hard to implement your own JavaScript "App start" functionality to do updates. The basic process is:

Check to see if you need to update
Ensure current user has permissions to do the update
Do the update

For more information check out this blog post the Chris O'Brien: JavaScript-based provisioning in SharePoint/Office 365
I plan on covering this in detail in a Pluralsight that I'm currently working on.
Answer: There is no initialization code that can be run when a SharePoint hosted app is installed unless you have set up a separate farm solution or remote event receiver. You can create declarative components in the app web, but as you've likely realized this does not work for creating items in the host web.
Additionally, since SharePoint hosted apps can only run JavaScript, all of the custom code they run must be done as the user who is using the app (there is no "app permission" level to leverage here). The app does not run the custom logic in your JavaScript, it is actually the users using the app that run the JavaScript defined there.
A common pattern to solve this issue is to direct the person who installs the app (who should have admin privileges on the site where they installed it) to visit a page on your app that sets everything up for them running under that user's privilege level. This can be the first place the full page experience in your app begins, you can later check if the setup has been run and direct users to other pages within your app as necessary.
There is some great information out there on implementing logic you would have previously put into a SharePoint customization (server or sandbox solution, for example), I would recommend reviewing the Microsoft Virtual Academy course: "Transform SharePoint Customizations to SharePoint App Model." as well as looking at some great examples on the Office Dev Patterns and Practices repository on GitHub. Specifically, you should find the information on the "provisioning pattern" useful; make sure you're looking at SharePoint hosted examples (often marked with the term "JSOM").


Joomla 1.7.3 Errors with Xampp 1.7.7

Question: I'm running windows 7, every time I try to install Joomla 1.7.3 on my xampp 1.7.7 setup to try and use Joomla, I get all these Strict Standard Errors:
<code>Strict Standards: Static function JDatabase::test() should not be abstract in     C:\xampp\htdocs\mysites\joomla_now\libraries\joomla\database\database.php on line 350

Strict Standards: Accessing static property JCache::$_handler as non static in C:\xampp\htdocs\mysites\joomla_now\libraries\joomla\cache\cache.php on line 394

Strict Standards: Accessing static property JCache::$_handler as non static in C:\xampp\htdocs\mysites\joomla_now\libraries\joomla\cache\cache.php on line 396
</code>
I've looked through most of the questions and answers for my problem, and they all say the same thing. look at the php.ini file. Fair enough, I would love to. But when I head over to C:\xampp\php to find it, there are two files. php.ini-development and php.ini-production.
I have made the changes to the error reporting on both, restarted xampp, switched versions of xampp and joomla multiple times, nothing works.
I have also tried to modify the .htaccess file for joomla with:
<code># supress php errors
php_flag display_startup_errors off
php_flag display_errors off
php_flag html_errors off
php_value docref_root 0
php_value docref_ext 0
</code>
and that doesn't work either.
If i create and run a phpinfo file to see exactly what file php is recognizing it tells me it's using C:\xampp\php\php.ini. I fail to understand how that is since there isn't just a plain jane php.ini file. I've looked. Numerous times.
Someone please explain to me what I'm doing wrong, or what I don't understand about these multiple php.ini files that never change anything, and I can't seem to make work. I would just like to install Joomla so I can see how to use it for a possible quick intranet setup.
Answer: Rename php.ini-development to php.ini. The php.ini-development file has the recommended settings for development and debugging while the php.ini-production file has warnings set to not display, etc.

Joomla 1.7.3 Errors with Xampp 1.7.7


Sharing internet connection between two laptops wirelessly

Question: I have two laptops. One of them is connected to the internet via a network cable. I want to share the internet connection with the second laptop wirelessly. How can i do this without buying a wireless router?
Comment: Have a look at this question: http://superuser.com/questions/44981/broadband-cable-to-wireless
Comment: And maybe this one

http://superuser.com/questions/18353/ad-hoc-network-internet-sharing
Comment: What Operating System?
Answer: If the laptop with the internet connection is running Windows 7, you can use Connectify to share the connection. It takes advantage of Windows 7's ability to make a wireless card appear as an access point, letting other computers connect through it without the hassle of an ad-hoc network. It will set up WAP encryption automatically, as well. I've used it before; it's very easy to set up and use.


Spin in Schrodingers Equations

Question: With the usage of Dirac notation we've gotten around a large amount of of inconvenience that would be dealing with spin. But, I was wondering, do we merely do this because it is inconvenient to try and create a differential equation with the corresponding spin or is it actually impossible to write that into the PDEs? If it's merely a matter of convenience, what would Schrodingers equation (or some kind of generalization that allows for you to include spin) look like?
Comment: I suspect either a) you basically would be needing to somehow remap your dimensions of the differential equations to some kind of basis that represents the group of your system and solve it there or b)you would be able to include a new separable term that is very weird to deal with calculus wise
Comment: Possible duplicates: http://physics.stackexchange.com/q/10837/2451 and links therein.
Answer: The Schrödinger equation is only correct in the non-relativistic limit $v << c$, for particles without spin. The correct equation for spinless (=spin $0$) particles is the Klein-Gordon equation, which reduces in the non-relativistic limit to the Schrödinger equation.
If we want to talk about spin $\frac{1}{2}$, the correct, relativistic equation is the Dirac equation. The Dirac equation reduces in the non-relativistic limit to the Pauli-equation, which is the analogue to the Schrödinger equation for particles with spin $\frac{1}{2}$.
For spin $1$ particles we have the Proca equation, which is known in the massless limit as the famous inhomogeneous Maxwell equation. For massless particles we have no non-relativistic limit and unfortunately I don't know the name, if there is any, for the non-relativistic limit of the Proca equation.
Comment: Note that the Schroedinger equation $i\hbar \dot{\Psi} = \hat{H} \Psi$ for the probability amplitudes $\Psi$ is always valid. The *single-particle* Shroedinger equation fails in the relativistic limit due to particle production and annihilation. This problem is remedied by using the correct many-body Hamiltonian $\hat{H}$ and wave function(al) $\Psi$ in the Schroedinger equation.
Comment: @StanShunpike Yes. The Schroedinger equation is a fundamental postulate of quantum mechanics and holds in both non-relativistic and relativistic settings. However, the degrees of freedom it describes in each of these settings are very different.
Comment: @MarkMitchison r u saying u can use the Schrödinger equation for relativistic stuff if you do this many body method ur describing?
Comment: @MarkMitchinson do you know some source that compares this method with the Dirac equation?
Comment: @StanShunpike "This method" that I am describing is just relativistic quantum field theory. The Dirac equation is only correct on shell, i.e. classically. However, the dynamics of the quantum state of the Dirac field is described exactly by the Schrodinger equation using the appropriate Hamiltonian (from which the Dirac equation can also be derived).
Answer: The Dirac notation is simply an alternative to vector notation. Certainly there are PDEs describing the quantum state of a lone particle with spin and they are:

The Pauli equation (see Wiki page of this name) was historically the first, and here the quantum state is two $\mathcal{L}^2(\mathbb{R}^3, \mathbb{R})$ functions of space and time. The two components encode the spin. Pauli built his equation with a phenomenological approach, looking primarily to the results of the Stern-Gerlach experiment. Importantly, Pauli consciously built the notion of spin into his equation;
Paul Dirac formulated the Dirac Equation in 1928; his motivation was to come up with a relativistic equation (unlike the 1926 Schrödinger and 1927 Pauli equations) and his method was to seek a "square root" of the second order operator in the Klein-Gordon equation, which was built to be relativistic but suffered from having negative as well as positive energy solutions. He hoped that a first order equation coming from the "square root" would overcome the negative energy solution problem. He realized he could not build such an equation with co-efficients in commutative fields such as $\mathbb{R}$ and $\mathbb{C}$ and so was forced to the idea of co-efficients from Clifford Algebras, represented by $4\times  4$ matrices (in case you've not met this before, one can represent complex numbers as a field of $2\times 2$ real element matrices, so the idea is not as unnatural as it first seemed to Dirac). So the operator takes a $4\times 1$ column vector as input, hence the question arose as to what the four components meant. It turned out "by chance" that the solutions modelled particles with spin; unlike Pauli, this had not been Dirac's main aim. His equation also had negative energy solutions, and he was forced to his Dirac Sea hypothesis to solve his original problem.
Answer: The Dirac equation is mentioned in other answers as PDE describing spin. As you ask "what would Schrodingers equation (or some kind of generalization that allows for you to include spin) look like?", the following may be relevant.
Yes, the Dirac equation adequately describes spin. However, it is actually a system of four partial differential equations for four functions (components of the Dirac spinor). It came as a surprise to me that the Dirac equation is generally equivalent to one PDE for just one function. I don't want to write it out here, but you may look at my article http://akhmeteli.org/wp-content/uploads/2011/08/JMAPAQ528082303_1.pdf (published in the Journal of mathematical physics). The equation is written in a more general and symmetric form in my recent article http://arxiv.org/abs/1502.02351 .

Spin in Schrodingers Equations


The first seven weeks of Daniel's 70 week prophesy

Question: I understand how Daniel's prophesy of 69 weeks until "Messiah the Prince" has been fulfilled (Daniel 9:25), but I have a question about the first seven weeks of his prophesy.  Was Jerusalem rebuilt in exactly 49 years (7 weeks) from the decree?  Or, was it "completed" in much less time, as most timelines seem to indicate?  Thank you.
Comment: Welcome to Christianity SE and thank you for your contribution. When you get a chance, please take the [tour] to understand how the site works and [how it is different than others](https://christianity.meta.stackexchange.com/a/1809/50259).
Comment: The OT prophetic voice ended after 7 weeks from 458 BC, and restarted again 62 weeks later with the start of the ministry of John the Baptist, AD 28, Luke 3:1.
Comment: Pls see my answer here:-  https://christianity.stackexchange.com/questions/71144/is-there-any-biblical-basis-for-400-years-of-silence-between-old-and-new-testame/71151#71151
 On this understanding the 7 weeks takes from the obedience to the decree to rebuild Jersalem on 3rd April 458 BC (Gregorian date) (Ezra 7:9) to the last piece of scripture added to the Old Testament (the book of Nehemiah).
Answer: Of the 49 years of that prophetic period given in Daniel 9, the temple rebuilding was put to a halt for about three years due to legal hassles.  Consider, for example, the record of Ezra 4:1-24.  Darius made a decree causing the work to stop as they were rebuilding the temple.
In the New Testament, the Jews show how well they remembered the events of those days--for they gave a count of how many years it took to rebuild that temple.

Then said the Jews, Forty and six years was this temple in building,
and wilt thou rear it up in three days? (John 2:20, KJV)

Taking the first seven weeks, therefore, as applicable to the period of the temple's rebuilding, we have a clearer picture of why they were marked off from the following 62 weeks of the 69 weeks.
The full prophecy is for 70 weeks.  Jesus also reiterated this prophecy.

Jesus saith unto him, I say not unto thee, Until seven times: but,
Until seventy times seven. (Matthew 18:22, KJV)

Here again is that prophecy in Daniel.

24 Seventy weeks are determined upon thy people and upon
thy holy city, to finish the transgression, and to make an end of
sins, and to make reconciliation for iniquity, and to bring in
everlasting righteousness, and to seal up the vision and prophecy, and
to anoint the most Holy.
25 Know therefore and understand, that from the going forth
of the commandment to restore and to build Jerusalem unto the Messiah
the Prince shall be seven weeks, and threescore and two weeks: the
street shall be built again, and the wall, even in troublous times.
26 And after threescore and two weeks shall Messiah be cut
off, but not for himself: and the people of the prince that shall come
shall destroy the city and the sanctuary; and the end thereof shall be
with a flood, and unto the end of the war desolations are determined.
27 And he shall confirm the covenant with many for one
week: and in the midst of the week he shall cause the sacrifice and
the oblation to cease, and for the overspreading of abominations he
shall make it desolate, even until the consummation, and that
determined shall be poured upon the desolate. (Daniel 9:24-27, KJV)

A "time" in Hebrew could also mean a "day" or a "year" (Hebrew word "yowm").  In the Jews' mind, therefore, it was a very small step to understand the connection between 490 "times" or "days" and 490 years.  This was something they should have grasped.  Jesus was seconding Daniel's 70-weeks' prophecy--and applying it to the times of the Jews' final probation as God's chosen ones.

70 weeks = 490 days
490 Years
Final period of Jewish probation
457 BC - 34 AD

7 weeks
49 years
Period of the rebuilding of the temple
457 BC - 408 BC

62 weeks
434 years
The silent period of awaiting the Messiah
408 BC - AD 27

1 week (split in halves)
3.5 + 3.5 years
Period of Jesus' ministry + Subsequent evangelism to the Jews until the stoning of Stephen
AD 27 - AD 30/31 (crucifixion) + AD 30/31 - AD 34

Back to your question about the first seven weeks--most of it, 46 years per the Jews' recollection to Jesus, was spent rebuilding the temple.  The few remaining years of this period comprised the times during which the temple's rebuilding had been stopped due to the determined resistance of the enemies of the Jews of those times such as Sanballat, Tobiah, and Geshem who wrote certified letters to the king to have the work stopped, and managed to succeed in their efforts for a short while.
From the start of the rebuilding to the completion of the temple, 49 years was the total.  It is interesting that the Jews did not attempt to exaggerate their figures to Jesus, but referenced only the time taken in actual construction, not including the delays.
Conclusion
The temple's rebuilding occupied the full 49 years of Daniel's prophecy, with 46 years of actual construction and the remainder consisting of delays, particularly near the beginning of their work, when the rebuilding was put to a halt by royal decrees.
Answer:
I understand how Daniel's prophesy of 69 weeks until "Messiah the Prince" has been fulfilled (Daniel 9:25)

Without presuming to read minds, I don't think you do; notice that the vision of Daniel 9 takes place in the first year of Darius (9:1), later identified as the fourth king before Macedon's conquest of Babylon (11:1-4); indeed, Darius II started his reign in 423 BCE, about 7 x 70 = 490 years before the fall of Jerusalem and its temple in AD 70, right in the middle of the Roman-Jewish war (66-73 CE), which lasted for about seven years (9:27).
Of course, one might reasonably object by saying that the text explicitly points to the decree of rebuilding the temple (9:25), issued in the first year of Cyrus (2 Chronicles 36:22-23, Ezra 1:1-2, 5:13-17, 6:3), not Darius; technically true, but please note that Daniel conflates the two historical characters elsewhere (5:30-6:1), where two of Cyrus' deeds (the conquest of Babylon at the age of sixty-two, and the division of his new empire into satrapies) are nominally ascribed to Darius.

Was Jerusalem rebuilt in exactly 49 years (7 weeks) from the decree?

The text you are trying to interpret (9:25-26) places a messiah or anointed one about half a century after the first year of Darius II (423 BCE), which the text conflates with Cyrus II, as shown above; indeed, Darius III, the king mentioned in 11:1-4, whose loss of the empire to Alexander is described in the preceding chapter (Daniel 8), was born around that time (~380 BCE).

en.wikipedia.org/wiki/Daniel_8
en.wikipedia.org/wiki/Darius_III

Now, John's gospel (2:20) does mention Herod's architectural endeavors, confirmed by the ancient Jewish historian Josephus Flavius in his books on the Jewish War, to have lasted for 46 years.

en.wikipedia.org/wiki/Second_Temple#Herod's_Temple
en.wikipedia.org/wiki/Herodian_architecture#Herod's_Temple
en.wikipedia.org/wiki/Herod_the_Great#Architectural_achievements

Also, unlike the Synoptics, John places the event at the beginning of Christ's ministry, rather than at its end (Matthew 24, Mark 13, Luke 21). Furthermore, his is the only Gospel to explicitly mention said ministry spanning over three distinct Passovers (2:13-23, 6:4, 11:55-19:14). All in all, the natural interpretation is that there were 46 + 3 = 49 = 7 x 7 years from the beginning of Herod's (re)construction efforts, until the end of Christ's earthly ministry; this seems alluded to elsewhere in the same gospel (8:57).

The first seven weeks of Daniel’s 70 week prophesy


Data Sync from Salesforce to Pardot

Question: I just wanted to understand one thing here for Pardot syncing, what happen when I unverify the connection and migrate data into Salesforce? does this migrate all the leads/contacts from Salesforce to Pardot automatically when enable connection again?
Answer: The connector does not create prospects retroactively. If you use the setting 'Automatically create prospects in Pardot if they are created in Salesforce', those prospects are created only after the connector is installed and this setting is enabled. This is what pardot documentation says about this:

Pardot creates a prospect when a lead or contact with an email address
  that is not already associated with a prospect is created in
  Salesforce. An email address is required on the lead or contact record
  to sync to Pardot. This setting is not retroactive and creates
  prospects only for those leads and contacts created after this setting
  has been enabled.

However, if this feature is enabled later on, then leads and contacts with email addresses that were created after the Pardot package was installed in Salesforce will be pushed down to Pardot. So when you reverify and you have not removed the Pardot package from Salesforce, Leads and Contacts created in the meantime will sync.
Alternatively, create a report of all new leads and contacts after unverifying the connector, and add these leads and contacts to a campaign in order to push those campaign members to a pardot list after reinstalling the connector.
Comment: Hey Thanks Fred for your reply, actually i found the answer which is matching with yours. Just wanted summarized here like, if package is already installed, checkbox "Automatically create prospects in Pardot if they are created in Salesforce" is checked and you have unverified the connection for migrating data into Salesforce then it will sync all your data (Lead+Contacts with email id) into pardot automatically. And if that checkbox was not checked at the time of yous migration and in future if you enable that checkbox in that case it also sync the migrated data into pardot.
Comment: Hi Dildar, you are right about this. In fact given your use case this behaviour is to your advantage. I edited my answer to reflect this. This only works if you didn't remove the Salesforce package since only Leads and Contacts that are created after the installation of the Pardot package in your org get synced.

Data Sync from Salesforce to Pardot


Simplifying geometry

Question: first of all, let me tell you I'm a total novice in 3d modelling, my experience is with Sketchup only.
Recently, I came in need of a particular model, and I got it in a STL format.
Sketchup imported it just fine, however, the mesh is so loaded with unnecessary details, it makes the application just freeze.
I was told Blender can solve this problem, so I came here to ask you how can I make it a clean mesh, without losing detail but making it lighter so the software can run (and no, it's not a hardware problem, I'm using a GTX 1070 with 16gb ram and up to date processor)
This is what I'm talking about:
https://i.stack.imgur.com/8nGuf.jpg
Sketchup can't handle that many faces.
So, how do I fix it using Blender?
Answer: There are a couple of things to reduce the meshes.
You can find the most part in the Mesh > Cleanup menu.
Remember you have to enter the Edit mode.
Also a Mesh > Faces > Tris to Quads helps to reduce the edges.
See the image below:
Comment: Also try the Decimate Modifier and lower the Ratio slider.

Simplifying geometry


Multiple subfaction leaders

Question: Is it possible to have more than one Illuminati, Mason, Inquisition, or Cult Leader in a game? If so, would they still have their individual recruits or would it be combined as if there was only one leader?
Would it also effect roles such as Mason sergeant, who gets a recruit if their leader is dead? If a scenario where one leader would die and not the other were to occur.
Answer: Multiple sub-faction leaders make 1 large sub-faction (See: ext-100 when Mason Leader was introduced).
Each leader has their usual pool to recruit from (X recruits per leader) but they all join the same large sub-faction.
Mason Sergeant only activates when all leaders are dead.
Other roles that interact with leaders (eg, Lost Mason) will also work when finding any leader.

Multiple subfaction leaders


What is Minority Carrier Storage Time?

Question: I know that Minority Carrier Life-Time is the time difference Between generation of minority carrier & their Recombination. I am bit Confused Between  Minority Carrier Storage Time &  Minority Carrier Life-Time, are they same thing or Different.
Comment: -1 for being too lazy to spell out whatever "b/w" and "B/w" are supposed to mean.  No, it's not obvious.
Answer: As far as I know there are two differents things.
Minority carrier life-time is the time for electron and hole concentrations, changed for any cause (radiations temperature, etc.), to return to their equilibrium concentrations.
Minority carrier storage time is stricly related to junctions.  The well know  Space-charge region act like a capacitor, and the stored charge are minority carrier, in both P and N regions.
In steady state the diffusion phenomena are terminated and we have electrons stored in P and holes in N region. If I apply a voltage I change this charge accumuled to the spatial charge region until it reach anoter equilibrium state. Then if I change the bias the charge stored change another time.
The time for the stored minority charge to become zero is called storage time.
See this picture, from the venerable Millman - Halkias "Integrated Electronics".

If you understand this for the p-n junction it is easy to apply to the mosfet channel region.

What is Minority Carrier Storage Time?


Where can I find the field string length?

Question: I need to import addresses using the API. Some addresses go over the CiviCRM limit. For instance street_address has a limit of 96 characters. I would like to know where are these limits defined in CiviCRM or where are they documented? I don't want to use the trial and error method to find out.
Answer: These are defined in MySQL. Adjusting the length of those tables should cover this.
With some data entry, making the changes through the interface can increase the length of the tables in the system.
John
Comment: Ok, I did `ALTER TABLE civicrm_contact MODIFY external_identifier VARCHAR(128);` but I still get the error _Value for external_identifier is 67 characters  - This field has a maxlength of 64 characters._
Comment: Yep ditto. needed to import Case Subjects that were > 128 so just altered the VarChar length in db but the import still rejects the longer ones.
Comment: Do you have logging turned on, and did you clear caches?
Answer: That field is defined at https://github.com/civicrm/civicrm-core/blob/master/xml/schema/Core/Address.xml#L92. It is run through GenCode.php to create the definition of the field and table used in the database installation. This also creates the definition in DAO file (CRM/Core/DAO/Address.php):
<code>'street_address' => array(
      'name' => 'street_address',
      'type' => CRM_Utils_Type::T_STRING,
      'title' => ts('Street Address') ,
      'description' => 'Concatenation of all routable street address components (prefix, street number, street name, suffix, unit
  number OR P.O. Box). Apps should be able to determine physical location with this data (for mapping, mail
  delivery, etc.).
',
      'maxlength' => 96,
      'size' => CRM_Utils_Type::HUGE,
      'import' => true,
      'where' => 'civicrm_address.street_address',
      'headerPattern' => '/(street|address)/i',
      'dataPattern' => '/^(\d{1,5}( [0-9A-Za-z]+)+)$|^(P\.?O\.\? Box \d{1,5})$/i',
      'export' => true,
      'table_name' => 'civicrm_address',
      'entity' => 'Address',
      'bao' => 'CRM_Core_BAO_Address',
      'html' => array(
        'type' => 'Text',
      ) ,
</code>
I bet that the generic import code truncates varchars to the maxlength of the field. So you could override this file to change that behaviour.
FWIW, on a buildkit development site you can set things up to re-run the GenCode so that change the xml for schema will be reflected in the regenerated DAO file.
If you want to propose a change to the schema in core, you will need to include in the PR an ALTER TABLE query in the appropriate file for the release in https://github.com/civicrm/civicrm-core/tree/master/CRM/Upgrade/Incremental/sql, eg 4.7.28.mysql.tpl. Increasing the field length doesn't involve loss of data or any need to convert the existing data, so it would be a straightforward change.
However, I'm not sure whether proposing a change to a field that has been unchanged since version 1.1 will get the community approval ideally required for a schema change. FWIW, I'm mildly supportive and this has caused us grief over the years. I'd also try to review what impact a longer field might have on layout onscreen, in address labels in core, and in html message templates, etc.


Number of certain (0,1)-matrices, Stanley's Enumerative Combinatorics

Question: Stanley's Enumerative Combinatorics (http://www-math.mit.edu/~rstan/ec/ec1.pdf) contains next fact:
1.1.3 Example. Let f(n) be the number of n × n matrices M of $0$'s and $1$'s such that every
row and column of M has three 1's. For example, f(0) = 1, f(1) = f(2) = 0, f(3) = 1. The
most explicit formula known at present for f(n) is
$$f(n)=6^{-n}{(n!)}^2\sum\frac{(-1)^{\beta}(\beta+3\gamma)!2^\alpha 3^{\beta}}{\alpha!\beta!\gamma!^26^{\gamma}}$$
where the sum ranges over all (n + 2)(n + 1)/2 solutions to α + β + γ = n in nonnegative
integers.
I need proof of this fact. (i.e. reference to book or articles that contains proof this fact).
Comment: If it's not already mentioned in the book, you could ask Stanley.
Comment: Your question is totally valid, but I would like to point out that that example is presented to show you heuristically what "closed form" means in combinatorics, and you are by no means expected to derive or prove the correctness of that formula at that point.
Comment: I also cannot see how to show this; if you really want to know the derivation, you should try this: find f(3),...,f(7) (say), and plug it into OEIS (the Online Encyclopedia of Integer Sequences). There you will find the sequence, most likely, and also probably references to a proof.
Comment: It might help if you quote the formula
Answer: You want the coefficient of $x_1^3\cdots x_n^3y_1^3\cdots y_n^3$ in $\prod_{i=1}^n \prod_{j=1}^n (1+x_iy_j)$. Expand the logarithm, delete all terms with an exponent greater than 3, apply the exponential function exp, and simplify. For a generalization, see the paper by Musiker-Odama at https://www.mtholyoke.edu/courses/gcobb/REU_MCMC/papers.html.
Answer: This problem was first solved by Ron Read in this 1958 PhD thesis. I didn't check if exactly this formula appears, but there are several that look very similar. One combinatorial way to prove it is like this:
Let $A_1,\ldots,A_n$ and $B_1,\ldots,B_n$ be disjoint sets of size 3. Consider bijections from $A_1\cup\cdots\cup A_n$ to $B_1\cup\cdots\cup B_n$. There are $(3n)!$ in total.  Use inclusion-exclusion to find the number such that each $A_i$ maps to 3 different $B_j$s.  (There are two things that can go wrong: mapping two elements of $A_i$ to two elements of $B_j$, and mapping all of $A_i$ to all of $B_j$; the counting is easy since the involved $B_j$s are distinct.) Then make an $n\times n$ matrix whose $(i,j)$ entry is the number of elements of $A_i$ which map to $B_j$. Finally, note that each matrix comes from $(3!)^{2n}$ bijections.
Answer: For $n=4$, there are $4$ options for placing the single $0$ in the first row, then $3$ in the second row, $2$ in the third row and $1$ in the fourth row, for a total of $24$. Searching for $1,0,0,1,24$ at OEIS yields OEIS sequence A001501; the entry contains lots of references.
Answer: An answer can also be found in the section 6.3 of the book "L. Comtet, Advanced Combinatorics, Springer 1974" and asymptotic formula $f(n)\sim e^{-2}36^{-n}(3n)!$ can be derived from a general asymptotic formula in the paper "C. J. Everett, P. R. Stein, The asymptotic number of integer stochastic matrices, Disc. Math. Vol. 1, No. 1 (1972) 55-72".


CP2102 with 3V Arduino and hardware

Question: My harware set up is: Arduino pro mini and nrf24l01 wireless module. This hardware is supplied by stabilized 3V generated by LDO from 1s li-pol. I need serial communication for debugging purposes, but I was wondering if connecting CP2102 to this harware set up does not damage the nrf24l01 module, which has max 3.6V VCC. Is it safe to use CP2102 with 3V supply from its regulator to my board, or not? Thanks!
Answer: I'm guessing you mean that you have 3.3 V on your Arduino. 3 V would be a bit too low.
Information that can be obtained from the datasheets:

NRF23l01 is 5 V tolerant on the datalines. Good to know but doesn't matter in this case
CP2102 has onboard 3.3 V
regulator and outputs 3.3 V levels.

So it seems safe to use it with the system. Make sure to connect the GND of the CP2102 with the device you're talking to.
From CP2102 datasheet:

CP2102 with 3V Arduino and hardware


Change of Roll moment with change of wing position (z-direction)

Question: If I compare two identical configurations, which only differ from each other in low wing and high wing position. We assume that the lift and drag remains constant. Will I get the same coefficients in moment for pitch, roll, and yaw? Because the force arms are the same?
Comment: I forgot to mention: i am looking at an axissymmetric (in x-direction) Body (tube) with a wing
Answer: For a first approximation, the coefficients will be similar enough, but not exactly identical. As you correctly point out the moment arms will be the same, but the interference effects of the wing-fuselage joint may not.
That is to say, your assumption that the lift distribution will remain unchanged will likely not hold out in reality.
The stability derivatives will not be similar, however.
Answer: If you have zero sideslip, then the moment coefficients will be similar between the two configurations. The only difference would come from difference in drag and its effect on moments, which would be small.
If you have non-zero sideslip, then the roll moment coefficients will be different due to dihedral effect.


Can Windows 8 be PCI compliant?

Question: I am in the process of getting PCI. I am in the last step in which I would need a secure PC on my internal network. All the scans I must run are only available through a plugin in browsers for Windows & Mac OS X (not for available for Linux which is the most secured). Anyway, I was trying almost all the Windows versions and I couldn't get PCI. Can Windows 8 get all the requirements to be PCI?
Comment: Which plugin are you trying to run?
Comment: It is a plugin called "iScan Online Browser Plugin"
Comment: Yes, but sadly you have to breach PCI compliance to be secure because you cannot get a list of updates that could possibly be applied anymore.
Comment: @Joshua you need to maintain a "software repository" host and configure your network to use that for system updates instead of whatever internet source they would normally use.
Answer: If desktop computers are within scope of your PCI boundary then they will have to be subject to the same controls as any other device in scope. This means a number of controls on the configuration, AV and malware protection, security policy (password management controls), etc. as well as processes around usage need to be considered. There is nothing specific that I have found about Windows 8 that means it can't form part of a PCI compliant solution.
Are you concerned about any specific control or process or any specific scanner result?
Remember that if a specific scan plugin fails against a device there is also opportunity to put in place compensating controls (though this is normally a last resort).
Comment: Thanks for the comments. Well, in last step "PCI DSS Internal Scan" it is required between others ...Checks including:
 Verification of inactive accounts
 Account lock out
 Screen saver grace period checks
 Time limit for active but idle terminal services sessions
 Time limit for disconnected sessions
 Minimum password length
 Password complexity
 Passwords are not older than 90 days
 Password History Check
And honestly, I have been trying in versions older than 8 and I would say is almost impossible to solve due to the scan or bugs on Windows, I don't know. But, I cannot get success at al
Answer: Do not include desktop machines in your PCI DSS scope any way you can avoid it. If the desktop machine is within scope, then the place it is in is also within scope, keep your offices out of scope any way you can.
Use a jump host with 2 factor authentication to connect to you PCI scope, it should keep any desktop boxes out of your scope.
Another thing is, if you are certain your system is up to date with latest CVE patches, go through the scan results and see if you can dispute the findings one by one. Typically the scans just check the software version numbers (they don't really try to perform the exploit) and CVE fixes are often backported when you use LTS OS distributions leading to quite a few false positives.

Can Windows 8 be PCI compliant?


Improve single HTTP transfer bandwith over high latency connection (Ubuntu Linux)

Question: I'm trying to improve the file transfer speed for my web server in Roubaix, France (hosted by OVH) over high distance/latency connections.
I know that TCP connections are affected by higher latency, however I've heard that tuning the TCP stack and using better congestion protocols can make a huge difference. I've seen whitepapers about TCP BBR pushing 10GB/s over high latency connections.
I'm expecting to push the connection near to the 1Gb/s limit, as I can with low latency (<20ms RTT) connections.
The server setup

OS: Ubuntu 18.04
Web server: Apache 2.4.29
Connection: 1Gb/s

Test file: Ubuntu 17.10.1 ISO (1.39GB)
Test "clients":

OS: Windows Server 2016
Connection: 1Gb/s

Locations:

New York, USA (73ms RTT)
Sydney, Australia (also OVH network, 267ms RTT)

Results:
New York has a download speed of around 3.2 - 3.4 MB/s
Sydney has a download speed of around 900-950KB/s
What's interesting is that using a download manager, to create more HTTP/TCP connections causes an increases in the download speed. Meaning the link is not saturated.
Tested tweaks:
First I've tested with several TCP congestion protocols:

TCP Cubic (default)
TCP BBR
TCP Hybla
H-TCP

Changes in the congestion protocol make almost no difference, at most 200KB/s on the New York connection and <50KB/s on the Sydney connection.

I've also tried setting other kernel parameters, such as the ones suggested here:
https://medium.com/@frjalex/linux-kernel-high-performance-networking-how-to-2d35f5900974
These settings have no observable effect on the download speed.
Question
How can I tune the Linux TCP/IP stack, so that single TCP (HTTP) connections max out the available bandwidth on high latency connections?
Issue
After running a test with wget on Linux I found that the issue was with the testing clients.. Apparently Windows (server 2016) does not increase the TCP receive window enough to maximize the connection..
Answer: After running a test with wget on Linux I found that the issue was with the testing clients..
Apparently Windows (server 2016) does not increase the TCP receive window enough to maximize the connection..


Getting the right version of datacube-explorer

Question: How can I get the right version of datacube-explorer-2.5.4? Because a try to install this one https://github.com/opendatacube/datacube-explorer/releases but doesn't work for me.
Answer: That page does have the latest stable version.
Extract it to a directory, enter the directory, and pip install .
If you're seeing an older version after running those steps, perhaps try uninstalling any older installs first with pip uninstall datacube-explorer, and then try again with the setup and run instructions. Pip may be skipping the install if you have an older dev version installed.


How to associate all extensions with their respective programs by XFE file manager?

Question: Trying to open any file in the XFE file manager, I have to associate the program to its file format, such as PDF format have to inform the evince program, as shown below. I wonder if there is a simpler way to associate all file extensions with their respective programs by XFE.
Answer: Try using xdg-open (its full path is /usr/bin/xdg-open and it should be installed by default; no need to install it manually).
xdg-open is a program that "opens a file or URL in the user's preferred application. If a URL is provided the URL will be opened in the user's preferred web browser. If a file is provided the file will be opened in the preferred application for files of that type."
You can find more information at http://www.ubuntugeek.com/xdg-open-%E2%80%94-opens-a-file-or-url-in-the-users-preferred-application.html or by running man xdg-open.
Comment: In the window in your screenshot, that says "open selected files with..." type `xdg-open` into the box, and make sure the "associate" checkbox is selected. It should open the file with the correct program (a PDF will open with evince,  a URL will open with Firefox, a .odt file will open with LibreOffice, etc). Now, the next time you try to open a file of that type in XFE, it will open it automatically without asking. You will have to do this for each file type (but you can use `xdg-open` for all of them)
Comment: Hello @Nick Weinberg,  thank you so much for the information! I am Ubuntu novice user, you would know tell me how to use the XFE file manager with xdg-open?
Comment: I found another problem when you click a picture, to take the test with `xdg-open` and the image is automatically opened with the gimp program, but I did not want to open it with the gimp, but with the default image viewer of Ubuntu, you could tell me how to do in this case?
Comment: You'll have to right-click on the image in XFE, choose "Open with.." and type the name of the program manually (`eog` for Eye of GNOME image viewer or `shotwell` for Shotwell photo program). If you choose the "associate" checkbox, the next time you open that type of image from XFE, it will automatically open it with the same program. You will need to do the "Open with..." step for each image type.
Answer: The default PDF viewer in Ubuntu is Evince. This is located in /usr/bin. So go there and select evince. Then XFE will open PDF files as normal.
Comment: I'm sorry, I don't understand the question. Can you please elaborate? In the original question, you asked only for PDFs. If you need something else, you could edit the question. Do you want XFE to associate programs for **all** extensions?
Comment: Hello @luchonacho, thank you so much! It really works, but I associate all programs to their respective file formats? Is there any other simpler way to do this?


With regard to ARMA time series, what exactly is eacf (extended auto-correlation function)?

Question: I'm going through my copy of Analysis of Financial Time Series, 2nd Edition, and I'm at the ARMA portion. One of the techniques for model selection is computation of the extended auto-correlation function, which indicates that, in a table of EACF's with MA coefficients listed across the top and AR coefficients listed down the side, the top-leftmost EACF that is less than the absolute value of 2 times the standard error of the EACF is at the position that indicates a good choice for the orders of the model. Can someone please explain to me exactly what the EACF is?
Answer: http://faculty.chicagobooth.edu/ruey.tsay/teaching/bs41910/lec9.pdf has some info. These are Tsay's lecture notes, and Tsay seems to be the co-developer of this measure.
Answer: Chapter 2 of Alan Panratz's Forecasting with Dynamic Regression Models contains a short discussion about the extended autocorrelation function. The book provides two references for the reader interested in more detail. You may like to track them down and give them a read.
Wei, W. W. S. (1990). Time Series Analysis, Redwood City, CA; Addison-Wesley.
Tsay, R. S. and G. C. Tiao (1984). "Consistent Estimates of Autoregressive Parameters and Extended Sample Autocorrelation Function for Stationary and Non-stationary ARMA models," Journal of the American Statistical Association, 79, 84-96.
By the way, the EACF is basically another tool, like the ACF and PACF, for identifying the order of an ARIMA model.


Interchange of $\ell^r$ and $L^p$-norm

Question: Let $(f_i)_{i\in\mathbb{N}}$ be a sequence of $L^p$-functions. What is the relation between
$\Vert \Vert (f_i)_{i\in\mathbb{N}}\Vert_{\ell^r}\Vert_{L^p}$ and $\Vert \left(\Vert f_i\Vert_{L^p}\right)_{i\in\mathbb{N}}\Vert_{\ell^r}$, where $\Vert (f_i)_{i\in\mathbb{N}}\Vert_{\ell^r}$ means the pointwise $\ell^r$-norm.
Comment: I'm not sure what to make of $\|(f_i)_{i\in\mathbb{N}}\|_{\ell^r}$ when each $f_i$ is an $L^p$ function? Perhaps for clarity you could write in full your definitions of everything? E.g., what is the domain of $f_i$, are you using usual Lebesgue measure for $L^p$, etc.?
Comment: Can you explain better what you mean with $\|(f_i)_{i\in\mathbb{N}}\|_{l^r}$?
Answer: What you are looking for is Minkowski's inequality. If $p \leq r \leq \infty$ you have
$$ \| (\|f_i\|_{L^p}) \|_{\ell^r} \leq \| \|(f_i)\|_{\ell^r} \|_{L^{p}} $$
if on the other hand $r \leq p \leq \infty$ you have
$$ \| \|(f_i)\|_{\ell^r} \|_{L^{p}} \leq \| (\|f_i\|_{L^p}) \|_{\ell^r}  $$
The Wikipedia discussion linked to above is brief. Better to consult Inequalities by Hardy, Littlewood, and Polya.
Comment: The $\ell^r$ norm of a sequence $(a_i)$ is the standard definition $$ \| (a_i)\|_{\ell^r} = \left( \sum_{i \in \mathbb{N}} |a_i|^r \right)^{\frac1r} $$ Now that $(f_i)$ is a sequence of functions, the pointwise sum $\ell^r$ is the function $$ f = \|(f_i)\|_{\ell^r} $$ given by $$ f(x) = \left( \sum_{i \in \mathbb{N}} |f_i(x)|^r \right)^{\frac1r} $$
Comment: For Minkowski's inequality: the usual version is stated for $p = 1$ and $r \geq 1$ (or vice versa). To get the version above replace $f_i$ by $|f_i|^p$ and $p$ by 1 and $r$ by $r/p$ etc. Lastly, Minkowski's integral inequality is stated for arbitrary measures: if you replace one of the measures by the counting measure on $\mathbb{N}$ you get the infinite sum.
Comment: I'm sort of lost about the notations (both in the OP's question and this answer). I can't seem to understand the notation $\|(f_i)\|_{\ell^r}$, and how to map Minkowski's inequality to the statement above...
Comment: Thanks! $   {}{}{}{}{}   $

Interchange of $\ell^r$ and $L^p$-norm


Intrumental variable for covariates

Question: I am only interested in the causal and unbiased effect of x on y and I have used additional covariates in my model to control for other effects. I have a pretty decent instrument for my potentially endogenous explanatory variable x. Do I have to instrument for other covariates, if I suspect them to be endogenous too. In fact, what about if I just leave the other endogenous variables out of the regression, while just use the instrument for my endogeous variable in consideration?
Answer: I have just given an answer here to a related question with a bit more maths, but here is just the gist of it applied for your case.
In practice I have come across many high grade papers where the authors just instrument for the one variable in consideration, while ignoring a few other dubious other covariates. However, from a purely theoretical standpoint, they should have controlled for all other explanatory factors that are under the suspicion to be endogenous--as long as you think that these explanatory factors are necessary to control for to satisfy the validity assumption of your instrument.
Let's rehash: A proper instrument is one that is correlated with your endogenous regressand after partialling out any other explanatory variable. Further it is uncorrelated with the error term of the original relationship. In your case, one of the explanatory variables related to the instrument is endogenous and potentially biased.
Assuming that your explanatory variable is endogenous too, as long it is relevant in determining Y, it adds to your instrument being informative, which is a good thing. The question is, if the instrument remains valid when controlling for some explanatory variables that are endogenous.
The validity assumption of your instrument practically a question of logic (unless you find a way test it do a thorough identification strategy). Insofar, if you believe that your edogenous other explanatory variable is necessary to partial out the effects in your instrument, then it may harm the validity assumption of your instrument.
Card (1992) instruments "years of education" with "travel distance to school" to determine the return on wages. He assumes that "intelligence" or "ability" are confounding factors that have not been controlled for. "Education" is therefore assumed endogenous as it relates to "ability". It is wickedly conceivable that "distance to school" is related with "age" which is assumed to be related with "wage" but also "ability", as for example, older people live farther away from cities where schools were built but may be less/more able as they are a different generation.
If age is endogenous for some reason and thus biased, it might invalidate your instrument, since you assume you have controlled for age that was necessary to do so to have your instrument being valid, in other words, you wanted distance to be unrelated with ability when keeping age constant.
By how much the validity of the instrument suffers, it is difficult to say. My intuition is that this is not a big thing if one or two other explanatory variables among a vector of several other determinants are endogenous; however, before you jump into conclusions, if you have established instruments for your other explanatory variables, use them by all means. It will add to the credibility of your hypothesis.

Intrumental variable for covariates


Installation on UEFI fails

Question: After installing Elementary (latest version, July 2021) from a USB stick, computer get's UEFI errors when rebooted. The only way to get the installation correct is to disable UEFI and use legacy support, Elementary then works OK. It seems that GRUB is not properly installed/configured, the 1st time installation actually showed a GRUB error. In this same computer I just installed Ubuntu 20 LTS on UEFI and it works w/o issues (Ubuntu and most Linux distros use GRUB, Elementary seems to use GRUB2). My laptop is a Lenovo Idea Pad 5 Flex (end of 2020 model).
Comment: Having the same issue with Dell XPS 15 and the final release of Elementary OS 6.0 (Odin).
The BIOS is configured to UEFI without security. And I getting error following error message:
`Failed to open \EFI\boot\[?] - Invalid Parameter
Failed to load image \EFI\boot\[?]: Invalid Parameter
start_image() return Invalid Paramater`
Answer: If you do not have a dual OS installed, then just go with the Legacy, but if that is not the case, you are advised to partition your driver as GPT before installing any OS then install burn your OS as GPT & UEFI. try this and let me know.
Comment: I already a a separate partition that had Ubuntu, I simply selected the same partition and reformatted. I have done the same thing for other Linux distorsionada, always works, Elementary is the 1st one that doesn't.

Installation on UEFI fails


Google "Play Music" app constantly running!

Question: Why is Google Play Music constantly running on my galaxy s4? I don't use any music app.
NOTE this has been previously posted but the answer given does NOT work

Go to Settings→Apps→Manage Apps
Go to the All tab
Scroll the list until you find Google Play Music
Tap the entry
On the screen which opens on the tap, you'll find a button labeled
Disable -- push it.

THEN it asks you to press OK or Cancel, pressing OK, then it says "Do you want to replace this app with the factory version?
A little bit of a merry-go-round, the s4 for is so full of crap that you CAN'T remove its a real JOKE - samsung are fools for thinking anyone would use have the space wasting crap on an otherwise great phone
Answer: Well, it looks like your only option is to root the Samsung Galaxy SIV and delete the google play music app and other bloatware from your service provider.

Google “Play Music” app constantly running!