Whether to use t-test for control and experiment means

Question: To measure the effectiveness of a marketing campaign, I have divided my customers in two groups. The experiment group, which is exposed to my campaign and the control group which is not exposed to the campaign. Experiment Group, Sample size is 10,000 and Control group sample size is 1000. My outcome is the buying response from the customer. So, the customer can buy irrespective of whether he/she is exposed to the campaign.
I want to analyze the effectiveness of my campaign and find out whether the proportion of customers who bought, differs in the two groups - experiment and control.
Shall I perform a t-test? My data is actually binary. The customer either buys or doesn't. Also, how should I determine my sample sizes for the control and experiment groups before conducting the exercise.
Answer: "Shall I perform a t-test?"  No.  A t-test assumes that the dependent variable is continuous in nature.  As you mention, your dependent variable is binary in nature, making a t-test inappropriate. See e.g. Wikipedia Student's t-test assumptions.
Instead you can use tests designed for counts, such as a test of equal proportions or chi-square test of association.  An example is given below with code for R.
The question of sample size may need to be a separate question.  There are methods to calculate the sample size needed for a chi-square test.  (See for example the section on power analysis at the bottom of Handbook of Biological Statistics: Chi-square.  However, in your case there is a secondary consideration in that you probably won't want to divide your sample equally, between an established ad campaign known to be effective and an experimental one.
Researching A/B testing in general may be helpful.
The following examples assumes that in the Control group 200 out of 10000 purchased, and in the Campaign group 30 out of 1000 purchased.
Resources:
### http://rcompanion.org/handbook/H_10.html
### http://rcompanion.org/handbook/H_04.html

Install packages:
if(!require(psych)){install.packages("psych")}
if(!require(DescTools)){install.packages("DescTools")}
if(!require(ggplot2)){install.packages("ggplot2")}

Test of equal proportions.  Results show that the campaign was more effective.  Proportion purchasing was 2 % for Control and 3 % for Campaign. This was a significant difference (p = 0.046).
Bought = c(30, 200)
N      = c(1000, 10000)
prop.test(Bought, N)

# X-squared = 3.9656, df = 1, p-value = 0.04644
#
# sample estimates:
# prop 1 prop 2
#  0.030  0.020

Results will be similar with a chi-square test of association.  Note that here we need to use the Bought and NotBought, not Bought and Total N.
Input =("
Method               Bought   NotBought
Control               200      9800
Campaign               30       970
")

Matrix = as.matrix(read.table(textConnection(Input),
                   header=TRUE,
                   row.names=1))

Matrix

Determine the proportions in each row of the table.
prop.table(Matrix, margin=1)

#          Bought NotBought
# Control    0.02      0.98
# Campaign   0.03      0.97

Chi-square test of association. The result here is significant, suggesting there is an association between the campaign method and the proportion of recipients purchasing (p = 0.046).
chisq.test(Matrix)

# X-squared = 3.9656, df = 1, p-value = 0.04644

It is important to look at the size of the effect.
One method is to look at the difference in the rates, in this case 2% to 3%. Is this a meaningful difference for the business, especially considering any additional costs of the campaign?
Another method is to use an effect-size statistic.  In this case (a 2 x 2 contingency table), the phi statistic can be used.  It ranges from 0 (no association) to 1 (perfect association), with a + or - depending on direction of the association.  This is a standardized statistic for the degree of association in the table, so could be used to compare among other 2 x 2 tables.
library(psych)

phi(Matrix,
    digits = 4)

# [1] -0.0201

It is an assumption of the chi-square and equal proportion tests that the "expected" values aren't too small.  So, for example, if I were to change the counts of Bought to 20 and 3, the expected counts would be too low for this kind of test to be valid. However, Fisher's exact test could be used in this case since you are fixing the number of Control and Campaign counts.
chisq.test(Matrix)$expected

fisher.test(Matrix)

# p-value = 0.04749

As a final note, it is useful to look at the confidence intervals of the proportions.  The code below gets a little complicated, but looking at the confidence interval for Campaign, it ranges down to almost 0.02, so we don't have much certainty that the proportion for Campaign is really that much different than for Control.  If the sample sizes were more uniform, we might have more narrow confidence intervals.
library(DescTools)

Campaign = BinomCI(30, 1000,
                   conf.level = 0.95,
                   method = "clopper-pearson")

Control = BinomCI(200, 10000,
                  conf.level = 0.95,
                  method = "clopper-pearson")

Data=data.frame(Method = c("Campaign", "Control"),
                Proportion.bought = c(NA, NA),
                LowerCI= c(NA,NA),
                UpperCI= c(NA,NA))

Data[1,2:4] = Campaign[1,1:3]

Data[2,2:4] = Control[1,1:3]

Data

#     Method Proportion.bought     LowerCI     UpperCI
# 1 Campaign              0.03  0.02033049  0.04255140
# 2  Control              0.02  0.01734654  0.02293792

Plot the proportions and confidence intervals
library(ggplot2)

ggplot(Data,
       aes(x     = Method,
           y     = Proportion.bought)) +

    geom_bar(stat = "identity",
             color = "black",
             fill  = "gray50",
             width =  0.7) +

    geom_errorbar(aes(ymin  = LowerCI,
                      ymax  = UpperCI),
                      width = 0.2,
                      size  = 0.7,
                      color = "black"
                      ) +

    theme(axis.title = element_text(face = "bold"),
          axis.text = element_text(face = "bold")) +

    ylab("Proportion purchased") +
    xlab("Method")


List of Exercises to Get Better in General

Question: Mediocre 2nd-year clarinet player here. Was wondering about a list of exercises to perform on a daily basis to generally improve. At the moment, I'm trying long tones, intervals, and chromatic practice, but nothing's really "sticking". I can play my band music consistently, but feel relatively stagnant otherwise despite practicing for several hours a day. My tone continues to suck and my finger speed has largely hit a wall. Where do I go from here, and how do I go about improving at this stage?
Comment: How long have you been doing these current exercises, and do you anything to switch up or take a break from that particular routine?
Answer: As a 'retired' clarinetist, I can offer a couple suggestions.
Daily:  long tones, for breath control and accuracy of pitch.
Daily: a variety of scale studies. One of my favorites is Stievenard, because it combines straight scales with interval studies, rhythms, and more.  Rotate thru the book to stay invigorated.
As to finger speed: there are several approaches, and your teacher should be able to help.  Pick any short passage, and play it very slowly until it's perfect. Move the metronome up a couple notches. Play until perfect. Repeat until MM = 240 :-) . This will not be a linear process, meaning there will be times when you can't do as well as you did the day or week before.  Be patient, and be diligent.
Most important rule, and I'm quoting a great teacher I know.

Most people practice until they get it right.  You need to practice
  until you can't get it wrong.

What this means: the temptation is to play a passage until you do it right, and then move on.  You have to play it until you get it right maybe 10 times in a row, so that your "muscle memory" remembers the right way, not the wrong way.


2 meter dipole of work vehicle

Question: I am about to purchase a Baofeng HT.  I have one I am thinking of using primarily in work truck.  I can't really drill holes or have antenna be too obvious.  On Amazon I found a 2 meter 70cm 2m dipole.  I am guessing it would have to be mounted vertically. It seems like it clips to inside of window.  I know it is not optimal but would it be better than stock ducky?  Has anyone used this antenna or have any ideas about really discreet antenna?
73 Joe
Answer: I intended on writing a comment but took up too much space.  I think your question is ripe for opinions and suggestions rather than answers.
However, I think if I were you I would operate first with just the antenna that comes with the HT before you decided you need something different from that.  A case in point.  I can generally reach all points of interest (a couple of repeaters in the area) with my HT without using a separate antenna.
But, in my pickup truck I also have a Yaesu FT-7800 (2m/70cm) rig and it has an external dual band (2m/70cm) antenna that has a easy to install and easy to remove antenna mount (screw clamp, no need for drilling holes).  It works fine too.
It really depends on who you are talking to (simplex or duplex/repeater) and where they are located and any obstructions (hills, buildings, mountains) that might be in the way.
By the way, my mobile 2m/70cm antenna is a Comet SBB-5NMO (i.e. with an NMO mount).  My clamp on mounting (supporting NMO mount) is also from Comet and model number CP-5NMO.  No, these are not the cheapest possible antenna solutions but I usually never go for cheapest.
Comment: It's going to depend on the characteristics of your vehicle.  I have a Baofeng UV-82.  The stock antenna works pretty well when I'm in my car (almost as well as the mag mount I have on the roof), but it doesn't work well at all in my wife's car.
Answer: If the antenna is small enough to fit on the inside of your window, then it must be a "shortened" antenna — a true 2-meter-band dipole is about 1 meter (1/2 wavelength) long. This means it will be relatively inefficient — just like the "rubber duck" antenna that would be supplied with your handheld. It will have the advantage of being closer to being outside the vehicle than wherever you're holding or mounting the HT, but that's not a whole lot of benefit, and it only works well on one side of the vehicle.
I would advise not bothering with it.
If you want an effective antenna which can be temporarily mounted, get a magnet-mount quarter-wave antenna for the roof.
If you want a better antenna which stays inside the vehicle, get a quarter-wave flexible whip antenna, such as the Comet SMA-24J. This will not give you great performance since it's surrounded by the metal of the vehicle, but since it's on the HT itself you can always stop and step outside to improve the situation.

2 meter dipole of work vehicle


Finding overall p-value for GLS model

Question: Does anyone know how I can find/calculate an overall p-value for a GLS multiple regression model (made with nlme)?
Comment: Welcome to SO. Your question is actually better suited for http://www.crossvalidated.com . Probably one of the mods will move it there soon enough. Next to that, I'd advise you to add some toy dataset and a reproducible example so people can play around a bit as well. It shows you did some effort, and people will be more keen to help you. On how to make a reproducible example, see [this question](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example)
Answer: The way one is expected to do this in gls() is to use a likelihood ratio test between two models via the anova() methods for "gls" objects. This is a general way of comparing two nested models with one another, but because of the way these models are fitted (REML estimates are used by default as one is generally fitting variance parameters for the correlation or weights arguments, but to compare models with different fixed effects we need ML estimates), you can't really get the significance of the overall model - it depends what you are wanting to test - the fixed effects or the variance parameters for the variance-covariance matrix?
Here is an example using data from the nlme package.
require(nlme)
fm1 <- gls(follicles ~ sin(2*pi*Time) + cos(2*pi*Time), Ovary,
           correlation = corAR1(form = ~ 1 | Mare))

There are two things to test in that model:

The fixed effects terms
The need for the correlation term

Lets assume the interest is in the fixed effects terms. We need an appropriate Null model that does not include these terms but does include the intercept and the same correlation estimate from the candidate model above.
fm0 <- gls(follicles ~ 1, Ovary,
           correlation = corAR1(value = 0.7532079, form = ~ 1 | Mare,
                                fixed = TRUE))

(I got the value by looking at intervals(fm1). Both these models have been fitted using REML, which is not useful in testing models with different fixed effects, however, REML gives unbiased estimates of variance parameters (for the corAR1() bit, hence we used that first.)
To check if the fixed effect terms are significant, we use anova() on the updated models that are fitted using ML:
fm0.ml <- update(fm0, . ~ ., method = "ML")
fm1.ml <- update(fm1, . ~ ., method = "ML")
anova(fm0.ml, fm1.ml)

which gives
> anova(fm0.ml, fm1.ml)
       Model df      AIC      BIC    logLik   Test  L.Ratio p-value
fm0.ml     1  2 1588.169 1595.629 -792.0844
fm1.ml     2  5 1574.387 1593.037 -782.1934 1 vs 2 19.78195   2e-04

As I used the same estimated correlation structure in both models (based on REML estimate from fm1) the difference between the two is isolated to the two fixed effects. However, the difference in degrees of freedom is not right here; because I fixed the value of the AR(1) parameter, the software doesn't treat that as a degree of freedom used, hence it thinks that the models differ by 3 instead of 2 degrees of freedom.
To address this we could just compute the p-value for the L.Ratio shown using the correct d.f.:
> pchisq(19.78195, 2, lower.tail = FALSE)
[1] 5.062956e-05

Or we could update fm1.ml to use a fixed estimate of the AR(1) parameter and redo the LRT:
fm1.ml <- update(fm1.ml, . ~ .,
                 correlation = corAR1(value = 0.7532079, form = ~ 1 | Mare,
                                      fixed = TRUE))

> anova(fm0.ml, fm1.ml)
       Model df      AIC      BIC    logLik   Test  L.Ratio p-value
fm0.ml     1  2 1588.169 1595.629 -792.0844
fm1.ml     2  4 1572.449 1587.369 -782.2243 1 vs 2 19.72008   1e-04

The reason for the difference in p-values between the two is the slightly lower L.Ratio for fm1.ml when fixing the AR(1) parameter.
If you want to check the need for the correlation structure, we need to use the REML estimated models:
fm2 <- gls(follicles ~ sin(2*pi*Time) + cos(2*pi*Time), Ovary)
anova(fm2, fm1)

> anova(fm2, fm1)
    Model df      AIC      BIC    logLik   Test  L.Ratio p-value
fm2     1  4 1804.868 1819.749 -898.4340
fm1     2  5 1571.455 1590.056 -780.7273 1 vs 2 235.4135  <.0001

Comment: Gavin - very nice explanation and examples, with code.  At first I was confused by the need to fix the correlation parameter $\rho$, but then I thought of an analogy with getting a likelihood ratio test for one of the regression parameters in the OLS univariate linear model case.  Do you fix $\sigma^2$ when comparing the two models, or do you let if float? [I'm ignoring the fact that we have an exact $F$ test in this case.]
Comment: @Frank Thanks. My first stab allowed $\rho$ to be re-estimated, but then I realised that the LRT would be comparing models with not just different fixed effects but different correlation structures. $\sigma^2$ was re-estimated. I'm not aware of a canned way with `gls()` to allow fixing that. I came at this from a practical point of view - re your comment in [...], what is the exact $F$? Showing my limited statistical knowledge now I'm afraid.
Comment: You're doing fine - this is a tricky issue that I wish I had figured out years ago.  Someone can probably point us to a good reference about what parameters to "freeze" when doing likelihood ratio tests, in general.

Finding overall p-value for GLS model


Can anybody identify this kind of plant?

Question: Location: Low Tatras, Slovakia, elevation: 1800 m. Can anybody identify this plant from Slovakia mountains?
Comment: Does it look like a young conifer?
Answer: I think this is some kind of Hypericum.  In Costa Rica and the Andes there is a high altitude ecosystem called the paramo in which shrubby Hypericum are characteristic species.  The area in your photo looks to be covered with shrubby species, and you are at decent altittude.  Looking at your picture (at full size) the leaves look approximately decussate which is typical of the genus, and also, the stems are ridged which is also pretty characteristic.
There is a good paper here on Hypericum of the Mediterranean region.  It mentions some groups that are shrubby or dwarf but thus far I have not been able to find a species that looks just like your picture.
Update: Possibly it is Hypericum aegypticum which looks about right relative to your picture, esp, the leaf color and size.  Also known to grow at that altitude. Decent picture here plus the one at Wikipedia both look similar to yours.
Update 2: On fresh look, the bases of the leaves for Hypericum aegypticum don't compare well to your picture, but I still think it is a Hypericum.


How to deal with a difficult team supervisor?

Question: I m in the fourth year of my PhD in veterinary sciences in North America. My Research project involves a lot of farm/team work. I have to work with technicians, farm staff, research associates and other students in the team as well as my advisory committee. I attended in many leadership workshops but still find it hard to deal with negativity, anger and control issues from one of my superiors. She in managing students as a research associate and has quite an influence on my advisor. She told me herself that she has chosen to be mean to people and has been humiliating others and me in various occasions. What should I do? How can I keep myself safe from anger, control issues and related stress?
Comment: I am unclear about your situation. Is she just your team mate? Is she also a graduate student? Does she have supervisory power over you? Have you talked to your advisor about it? You said she has quite an influence on your advisor. To what extent is this influence? Is she really indispensible? Can you continue your research without her?
Comment: I would suggest to get to know some previous cases of reporting a harassment at your university. Sometimes reporting is worse than solving the problem by yourself.
Comment: She is a research associate. Managing all the projects and lab works and teaching students new techniques. so in the beginning my supervisor asked me to check each experimental design specially if it involves farmwork with her. She has influence because she is scientifically good and knows what she is doing but unfortunately not in the case of professional behaviour.
Comment: In terms of reporting her I have talked and witnessed few other cases of harassment. University might help you to come out of the harassment circle but won't do anything to solve the problem. That person will stay in the university specially if she/he brings a lot of funding. so money talks at the end!
Answer: Being mean and humiliating anyone, let alone subordinates, in the workplace (academia or otherwise) is inappropriate and should not be tolerated. I would suggest you informally talk to whomever is in charge of harassment claims at your university to let them know what is up. Depending on how bad the situation is, you could either file a formal complaint or go talk to the person directly. By having the informal talk with HR you will be protected if your one-on-one discussion blows up.

She told me herself that she has chosen to be mean to people and has been humiliating others and me in various occasions.

It seems you have talked to her, but did you tell her that her attitude and behavior is making it difficult to do your job? Maybe you can work something out where she is less abusive to you or that your work environment is more structured to prevent the harassment. Hopefully that will resolve the issues, if not, file the complaint.
University's do not kid around with complaints about harassment. These types of formal complaints make promotion much more difficult and will often be reported in any reference written by the department head. They often will require the individual to receive training and monitoring. Once the possibility of a formal complain is on the table it is in the best interested for the colleague to do everything possible to prevent the complaint. Once a formal complaint is raised any escalation by the colleague will likely be dealt with swiftly and harshly by the University.
Comment: 'University's do not kid around with complaints about harassment' Sadly, they often do. Many academic institutions work as self-defending groups and there is always the risk of a backfire. I fully agree that abusive behavior should be systematically reported but OP should be aware of the associated risks. In this case, as it seems that OP is not a lone victim she should seek support from others and maybe take a common action.
Comment: Unfortunately @Jigg is right. I studied few other cases in our department and other faculties. It SEEMS that university cares but the actions are opposite and when things get serious they retreat and put their priorities first.
Answer: You seem to be close to completing your PhD so the usual answer here of "Run don't walk" don't seem to be the way out. Instead you need to find a way to go through the final time. I would strongly suggest seeking professional help. Hopefully your school has access to psychologists or the equivalent who can not only help out with personal problems but in your case, more importantly, how to manage difficult personalities. I have no doubts that it is and will be a burden at times but for you the question is finishing or not, what the effects on yourself will be and in the short of it, is it worth it if you add all factors together. Only you can answer that question. It does not seem as if you have come far down that path so trying to find the support and guidance from professionals on how to deal with difficult personalities is the best way forward. You will bump into these later in life as well so gaining understanding and acquiring strategies is never a waste of time.
Comment: Thanks @peter! I have been in few counselling sessions in university. Also read few books to manage last 4 years dealing with her. Takes lots of energy and time some times more than PHD workload itself. It's a life time process. Any book or website recommendation?
Answer: I'm sorry to hear this; such situations can be unbelievably stressful and upsetting. As you're in your fourth year, you're nearly there and have your own network, which are very helpful.
Such situations are tricky because they can degenerate suddenly and unexpectedly. The ideal (not always possible) is to avoid conflict at almost all costs. Conflictual people tend to be better at managing disputes that break out...they often have had a lot of experience of this and you might discover that they are uncomfortably well acquainted with university harassment procedures etc.
I would hesitate to make a formal complaint unless if the situation becomes unbearable, as things may escalate and affect your relationships with others in your department, which might cause delays to your PhD. Hopefully, you are known in your department and group as a positive team member who isn't associated with conflict. Maintain that reputation as long as you can.
I would also hesitate about approaching this supervisor one-on-one in order to directly address the behaviour. Any such discussion would need to be handled with extreme care so that your supervisor doesn't feel threatened. I would venture to suggest that avoiding any suggestion of threat could easily be impossible to achieve during such a discussion. It may be better to remain in the background as much as possible and minimize unnecessary interaction with your supervisor instead. Try to keep things very cool and professional.
Have you somebody more senior in the department you can confide in? A mentor would be perfect for this role, as long as they are discreet. Now would be a good time to request a mentor if you don't have one.
Although it's not nice to do, keep a diary of every incident, even if reasonably minor. Any unpleasant emails etc, keep them safe. This is because if things become more difficult, you might need every scrap of evidence.
I'd recommend pre-emptively reading the book by Bill Eddy "It's all your fault: 12 tips for managing people who blame others for everything" as he gives a lot of good advice for avoiding being dragged into disputes and minimizing their fallout when they do occur.
If things become absolutely impossible (hopefully not), it may be possible to remove this supervisor from your committee. This is where having an impeccable interpersonal record, the diary and an established relationship with a senior member of your department comes in.
To end on a positive note, I think a lot of academics at all levels have had experience of these sorts of situations and we've all survived! But I wish you and others who come to this page good luck.
Comment: Thanks @L Platts. I will take a look at the book. Remaining in the background and minimizing my interactions is what I have done so far in last 4 years. I survived but witnessed her behaviour and hurt for me and others. I also tried to talk to her but she gets even more angry and mean. Now that I have more power over my project and have my main supervisors's support I started to question my self? Is that it? Just stay quiet? As @peter Jansson said: I gonna bump to this later in life. How I gonna deal with it then? She seem to enjoy humiliating others, not the first case and not the last.
Comment: The book really helped me. It provided tools for life. I would have just written read the book in my answer, because its philosophy is difficult to summarize, but Stack Exchange suggests writing a fuller answer so that's where all the rest came in! I hope the book helps you too.
Answer: topic is never outdated. I was dealing with bullying supervisor as well. fortunately I have managed to change my supervisor in the middle of second year. As 'my therapy' I  wrote couple of blog posts about 'dealing with difficult supervisor'. Part one is about 'easy cases', part two is about more difficult and part 3 is about bullying monsters!!
enter link description here
Hope everyone who is dealing with a supervisor like mine is able to  get out of this situation  ASAP!
Thanks,
Monika
Comment: Can you put some excerpt from your blog into the answer? SE frowns upon link-only answers


Baking rewards as operations

Question: How do baking rewards appear on the chain when they are credited to the baker? Is it a 'transaction' operation? How do I go about identifying them?
Answer: The rewards happen as part of the protocol and it's all on chain. But they are not a "transaction" in the normal sense of the word, as usually a transaction requires some user intervention. But there is fundamental movements of funds from the "freezer" to the delegates. Conceptually, the freezer temporarily holds all the bonds and rewards for baking and endorsing.
To find this information on chain, we have to look at the very last block of the cycle we'd expect the reward.
blockNumForRewards = (rewardedCycleNum + 6) * numOfBlocksInCycle
For example, for cycle 93, the rewards for cycle 93 gets unlocked at the last block of cycle 98, so we need to look at block number (93 + 6) * 4096 = 405,504.
After we knowing the block number, We can query for the block with our node by getting the hash from a block explorer like tzscan. In this case, BLdha4dMeWYxYkuP46eCgYwsgBYiKPNFLvgiu5NqgdxPLhkgzUf is our block hash:
/chains/main/blocks/BLdha4dMeWYxYkuP46eCgYwsgBYiKPNFLvgiu5NqgdxPLhkgzUf

Obviously there is a lot of information in here, but let's focus on the path that handles the balance changes, specifically metadata > balance_updates. Example:
{
  "protocol": "PsddFKi32cMJ2qPjf43Qv5GDWLDPZb3T3bF6fLKiF5HtvHNU7aP",
  "chain_id": "NetXdQprcVkpaWU",
  "hash": "BLdha4dMeWYxYkuP46eCgYwsgBYiKPNFLvgiu5NqgdxPLhkgzUf",
  "metadata": {
    ...
    "balance_updates": [
      // this is what we care about
    ]
  }
  ...
}

This portion of the block is the balance updates that retains to what the protocol needs to apply regardless of the user interventions. In a lot of the blocks, this portion will just include the current block baker with its locked rewards and bonds. In the last block of the cycle, balance_updates also includes all the rewards and bonds unlocks for every baker that participated in cycle 93.
Anyhow, let's dig into the specifics of one baker to understand further. For illustration, I've filtered out transactions for one particular baker tz1ivoFE...TD.
    "balance_updates": [
      ...
      {
        "kind": "freezer",
        "category": "deposits",
        "delegate": "tz1ivoFEvbfbUNav5FwLvmxzMGcNXWxY9qTD",
        "level": 93,
        "change": "-10368000000"
      },
      {
        "kind": "freezer",
        "category": "fees",
        "delegate": "tz1ivoFEvbfbUNav5FwLvmxzMGcNXWxY9qTD",
        "level": 93,
        "change": "-9362"
      },
      {
        "kind": "freezer",
        "category": "rewards",
        "delegate": "tz1ivoFEvbfbUNav5FwLvmxzMGcNXWxY9qTD",
        "level": 93,
        "change": "-321000000"
      },
      {
        "kind": "contract",
        "contract": "tz1ivoFEvbfbUNav5FwLvmxzMGcNXWxY9qTD",
        "change": "10689009362"
      },
      ...

Inside of balance_updates array, it will include every "transaction" that needs to be adjusted for all these addresses including the "freezer". Each transaction also gives some clues on what they are for.
The above is pretty typical what we'll see per baker. There are 3 "freezer" related transactions and one "contract". The "freezer" transaction are different by their category (deposits, fees and rewards). The categories are pretty self explanatory. Just in case you are wonder, deposits and rewards will include both baking and endorsements bonds and rewards. Notice that those freezer operations are negative values and they imply that these balances are subtracted from freezer.
The "contract" transaction is what changes the balance to the baker in question. This is pretty similar to a user initiated transaction. If we add up the 3 freezer category's balances, they would add up to the change balance for the baker.
Comment: This is the correct answer. My answer answered the question of how baker credit/reward their delegators, not how a baker is rewarded via the protocol itself. To remove any confusion, I've deleted my answer.
Comment: @Frank how to know that "tz1ivoFEvbfbUNav5FwLvmxzMGcNXWxY9qTD" is the baker ?

2. Why deposits , fees and rewards all are in negative. Could you please help me understand ?
Comment: 1.That baker address is just an example, but this section only include bakers. 2. "Notice that those freezer operations are negative values and they imply that these balances are subtracted from freezer." Freezer is what the chain is storing, so we are making a negative balance change for the freezer and a positive balance change as the reward. It's zero sum.
Comment: @Frank I am still confused with the freezer stuff. I have seen few samples where deposit is positive and reward is also positive. In which scenario this is possible for this blochHash we can find the deposit and reward as positive
Answer: The "short version" answer is that this is accomplished through 'consensus', which is an extremely important concept in blockchains that are used for cryptocurrency.  Unfortunately many people just don't really understand it; in this aspect essentially the term "consensus" boils down to:
(and this really is a very simplified description here, not taking into account freezing rewards or deposits, etc)
The code for the Tezos protocol dictates that when an account bakes a block, that account's balance simply goes up by ꜩ16.  Since everyone is running the same protocol, everyone agrees that when an account bakes a block, that account's balance goes up by ꜩ16. That's consensus.

Baking rewards as operations


3 Cables in Switch Box and Can't Figure it out

Question: I had a ceiling fan with light in a cabin that I bought.  It did not work when we bought it.  I've replaced the fan, but the light doesn't work.  The wall switch has 3 cables inside.  Attached is an actual picture and also a diagram of what's inside the box (the diagram does not include the copper grounds which are twisted all together). I think that one of these cables goes to a nearby wall outlet, one goes to the fan, and one is to the circuit box.  But I'm not sure how to determine which goes where.  I have wired this thing up a couple times and can get the fan to spin but never can get the light to come on. (yes I've made sure the pull switches were tested too).  The wall Switch is one of those Lutron Fan and Light switches.  Can someone please help guide me on this?
Comment: Just so we've covered all the bases - you did check/replace the bulb right?
Comment: Remove the red from the red-black bundle.  Does one or more sockets lose power?  It may be one socket in a pair.  Turn power off at the breaker  while changing wires .
Comment: What does the wiring look like in the box for the fan? Specifically is there one house wiring cable in the fan box and is it one of the cables with the black, red, and white?
Comment: Per the answer by @longneck  you must have three wires to the Lutron combi fan/light switch. One will be an always hot (black) from the line. The other two will be "switched hots" going *to* the fan and light, respectively. In the fan box the fan switched hot goes to the fan lead (usu black) and the light switched hot goes to the light lead (usu blue).
Comment: brhans - Yes, light bulbs were checked
Harper - Yes, that wire connects the wall plug
Jim Stewart - it's a Hunter Fan, so its simple, blue/black/white.
Jim Stewart - I think you and @longneck are correct.  There is one hot wire back to the box.  I'm going to try that recommendation.

Thank you all so very, very much!
Answer: I'm going to guess that the upper left wire is the fan/light, and the lower right cable is the outlet. If this is correct, then this is how you need to wire it up:

If the fan and light don't work, try reversing the red and black wires connected to the FAN and LIGHT terminals of the switch.
If that still doesn't work, you'll need to identify the cable bring power to the box. If it's not the cable in the upper right, then you'll need to investigate the wiring in the fan box or the outlet box to make any progress.
Comment: I think what you have here is probably right.  yes, I think the upper left is the fan/light, the upper right is the outlet on the wall, and the lower right is what connects to the fuse panel.  If your drawing is correct, then I will pigtail a black wire off of the joins between upper right and bottom right - correct?  THANKS SO MUCH!!!!
Comment: Based on your photo, yes. You will add a pigtail to the existing wirenut on the black/black/red wires, and connect the pigtail to the LINE terminal on your switch.
Comment: It seems unlikely that the lower right cable would be from the fuse box, because it has a red traveler wire, whereas the fuse box would be sending white (neutral), black (line), and ground. Just pointing this out, as the comment suggesting so is contrary to the provided answer.


Relation between component and algebraic definition of covariant vectors

Question: I studied contravariance and covariance concepts in following way:
For any vector if we get its components by parallelogram way we achieve contravariant components, and if we want to get its components by orthogonal projection we achieve covariant components. For latter case we need reciprocal basis in order we can expand the vector by its covariant components. But I read somewhere, in fact covariant vectors are elements of dual space and they expanded by dual basis. My question is: how is the latter approach to covectors equivalent to previous approach?
Furthermore, I need some good explanation for latter approach to covariant vectors.
Comment: Let the vector space have basis vectors $\vec e_i$. Then the a vector $\vec v$ with components $v^i$ can be written as $\vec v = v^i \vec e_i$ (summation convention). The dual space has a basis $\vec e^i$ such that $\langle e^i, e_j \rangle = \delta^i_j$. Try [Applications of Differential Geometry to Physics](http://www.aei.mpg.de/~gielen/diffgeo.pdf) which I started to read yesterday.
Comment: Cross-posted from http://math.stackexchange.com/q/869877/11127
Answer: In a class I'm lecturing, I mention to my students (in a very, very elementary way) that vectors and covectors do not live in the same space.
It's a typical school phrase... "Do not add apples and pears", and it's true!
If you keep in mind the custom column and row representation of a vector, you can prove that both of them (by themselves) satisfy the usual axioms of a vector. However, you can not add a column and a row vector.
With this you now understand that all the time you've been working with two types of vectors.
The thing is that, they are not related with each other until you impose a relation between them, e.g., you identify their bases through the introduction of a scalar product $$\left<e^i\mid e_j\right>= \delta^i_j.$$
Since this identification can be seem as a map from vectors to scalars, one says that covectors are objects living in the dual space of vectors.

Updated answer
After reading your updated question I (believe) have understood your point.
It seems to me that you want to know the "difference" between (and relation among) the coordinates draw in blue and green in the picture below

The green coordinates are the contravariant components of the vector, defined by the "parallel" projection wrt the other axis. The blue coordinates are the covariant components of the vector, defined by "orthogonal" projection along each axis.
NOTE: in a rectangular frame these two coincide, and there is no ambiguity.
 Why are the blue one called "covariant"?
The usual answer is... because they transform as the basis! (Yes, sure... but I don't still get it!)
A base vector defines a direction, and a flow in that direction is defined via the (directed) gradient. The gradient is represented by the set of perpendicular (hyper)planes orthogonal to the reference direction. Thus, perpendicular to that direction... sounds familiar, THE BLUE COORDINATES!!!
Since the derivative can be written as $\partial_i$ let's denote this type of components by $V_i$
What about the green ones?
I could try to explain heuristically why these are denoted with an upper index, but in this stage let's mathematics do its job.
I'd do the following (I did it once and convince myself... so try to do it!):

By defining a vector basis in the non-rectangular frame (in term of the rectangular one), say $\{\vec{e}_1,\vec{e}_2\}$ in terms of $\hat{i},\hat{j}$ and $\theta$ the angle between the non-rectangular axis, Find the metric of the non-rectangular frame. $$g_{ij} = \vec{e}_i\cdot\vec{e}_j.$$
Then invert the metric,
Raise the index of the covariant vector using the inverse metric.

You will get exactly the component represented by the green projection.
Why are they called dual?
Because you can always define the action of one type over the other... resulting into a field ($\mathbb{K}$). Mathematically, these define the elements of the dual space.
In other words, if you say that $\{V^i\}\in \mathbf{V}$, then $\{V_j\}\in \mathbf{V}^*$

 It is not my idea, but you can read about that in (for example) the books by B. Schutz ("A first course in Genral Relativity" or "Geometrical Methods of mathematical physics", if I remember well).
A geometrical interpretation is that contravariant vectors are arrows, while covariant vectors are perpendicular planes to a given direction, the action of one over the other is the number of hyper-planes you intersect with your arrow. That is the connection.
In other words, you have related two unrelated vector spaces (say $\mathbf{V}$ and $\mathbf{U}$), by introducing a scalar product ($\cdot:\mathbf{V}\times\mathbf{U}\to \mathbb{K}$). This is equivalent to defining an action of $\mathbf{U}$ over $\mathbf{V}$ by $$\mathbf{U}:\mathbf{V}\to\mathbb{K}.$$
With the last map, you conclude that the introduction of a scalar product is equivalent to the identification of $\mathbf{U}$ with $\mathbf{V}^*$
Comment: @aminliverpool I just understood your edited question! I'll update my answer tomorrow ;-P
Comment: @aminliverpool What about now? I included an extra paragraph to explain the duality.
Comment: Thank you for your attention. I agree with you, but I think my question is still unanswered. I presented two ways for introducing covariance concept. I need demonstrating the equivalency of the two approaches.
Comment: Thank you for your answer. Ok. I agree with your description of covectors by projecetion, but in last section of your answer, I cant understand how you settled relation between projection description of covectors and dual space. I cant understand your statement: "Because you can always define the action of one type over the other... resulting into a field (K). Mathematically, these define the elements of the dual space.". Is it possible for you to explain more.
Comment: Thank you. I feel I near to solution of my problem. But one question remains: To obtain covariant component of a vector we should construct bases which are orthogonal to original bases. We can do that by construct reciprocal bases in our vector space and I think it is not necessary to extract such bases from the dual of the vector space, and decompose the vector on those bases. Can you help me, more ?
Answer: You may find this question and especially Emilio Pisanty's answer to be enlighting with regards to what co- and contravariant vectors really are.
Now, if I may rephrase your original question a bit: *How do parallelograms and lines in $\mathbb{R}^3$ relate to co- and contravariant vectors in $T_p \mathbb{R}^3$ and $T^*_p\mathbb{R}^3$?
The first one is easy. Take a line in $\mathbb{R}^3$. It has a direction $v = v^i e_i\in\mathbb{R}^3$. Identify $v\in T_p\mathbb{R}^3$ in the natural way (since $T_p\mathbb{R}^3$ is just $\mathbb{R}^3$, just give it the same basis $\{e_i\}$). You've got yourself a (contravariant) vector.
The second one is a bit trickier: Let the parallelogramm be spanned by $v,w \in \mathbb{R}^3$. Then, there is the natural notion of associating this area with the exterior product $v \wedge w$, which actually represents as $v \wedge w = v^i w^j e_i \wedge e_j$ an element of $T_p\mathbb{R}^3 \wedge T_p\mathbb{R}^3$, and could be seen as a constant 2-form. Now, identify the basis $\{e_i \wedge e_j\}$ of $T_p\mathbb{R}^3 \wedge T_p\mathbb{R}^3$ with the Hodge dual of the cross product as $e_i \wedge e_j = \star (e_i \times e_j) = e^k$, which is the dual basis of $T^*_p\mathbb{R}^3$. You've got yourself a (covariant) covector.
The above approach generalises nicely to the $\mathbb{R}^n$ equipped with some (Euclidean) metric (i.e. a scalar product, essentially):
Let $\{e_i\}$ be a basis of the $\mathbb{R}^n$ as a vector space. Let $v \in \mathbb{R}^n$ be a vector.
The contravariant components of $v$ are obtained by $v^i := (v,e_i)$, which is your orthogonal projection.
A basis for the hyperplanes $\Lambda^{n-1} \mathbb{R}^n$ (or "hyperparallelograms", if you prefer) is given by $\{e_{i_1} \wedge \dots \wedge e_{i_{n-1}}\}$. To be able to "project" $v$ onto it, you must either turn $v$ into an element of $\Lambda^{n-1}\mathbb{R}^n$ or turn the hyperplane into an element of $\mathbb{R}^n$, since you cannot take the scalar product of a plane with a vector. So, we let Hodge duality do its job, and say that the covariant components of $v$ are obtained by $v_i := (v,\star(e_{i_1} \wedge \dots \wedge e_{i_{n-1}}))$, where $i$ is precisely the index not ocurring in $\{i_1, \dots ,i_{n-1}\}$. Why is this covariant, you ask?
Because the defining property of the Hodge dual is $v \wedge \star w = (v,w)(e_1 \wedge \dots \wedge e_n)$. From plugging in $e_i$ for $v$ and $\star(e_{i_1} \wedge \dots \wedge e_{i_{n-1}})$ for $w$, you can see that  $\star(e_{i_1} \wedge \dots \wedge e_{i_{n-1}})$ precisely fulfill the relation for the dual basis to $\{e_i\}$ (you have to use that $\star^2 = -\mathrm{id}$ for $(n-1)$-vectors)
Therefore, we have shown by translating the geometric idea of projecting onto hyperplanes into precise mathematical language that it is exactly the same as expanding in the dual basis.
Comment: Thank you for your attention and your useful link. But I think my question is still unanswered. I presented two ways for introducing covariance concept. I need demonstrating the equivalency of the two approaches.
Comment: @aminliverpool: I have expanded my answer. If it is still not what you seek, I advise that you give a precise definition of what *you* understand under "projecting onto hyperplanes" in the OP.
Comment: Thank you for your answer. I am not familiar with "exterior product" and "Hodge dual", and so I cant understand your answer. My understanding of projection is the same as Dox explained in his answer. Is it possible for you to reanswer my question in a simple way?
Comment: @aminliverpool: It seems Dox (and others) do a far better job of thinking along geometric lines and easing down on the abstraction. All *I* could do is to explicitly construct why the exterior product and areas are intrinsically related, but I'm afraid that that would be more math that probably wouldn't help you.
Answer: "Covariant vectors as expressed in  a dual basis" is exactly the same thing that "orthogonal projections to achieve covariant components"
Choose one generating system $\vec e_1, \vec e_2$, non necessary orthogonal, a vector $\vec v$ may be expressed by $\vec v = v^1 \vec e_1 + v^2 \vec e_2$. The coordinates $v^1, v^2$ are called contravariant coordinates of the vector $\vec v$
Now, let a new generating system $\vec f^j$ be a dual of the generating system $\vec e_i$. This is expressed by $\vec f^j.\vec e_i = \delta^j_i$ (this is the definition of "dual")
This means that $\vec f^2.\vec e_1 = \vec f^1.\vec e_2 = 0$
So, this means that $f^2$ is orthogonal to $\vec e_1$, and that $\vec f^1$ is orthogonal to $\vec e_2$
The coordinates $v_1, v_2$ of the vector $\vec v$, relatively to the generating system $\vec f^j$ are the covariant coordinates of $\vec v$ :   $\vec v = v_1 \vec f^1 + v_2 \vec f^2$
Now, to find $v_1$ for instance, you have to take, from the arrow of the vector, the parrallel to $\vec f^2$, but we have seen above that $\vec f^2$ is orthogonal to $\vec e_1$, so " take the parrallel to $\vec f^2$" is the same thing as "take an orthogonal to $\vec e_1$"
That's how you get your orthogonal projections to achieve covariants components.
UPDATE
Considering covariant  dual vectors as linear functions from vector space to $\mathbb R$, $f^i$ are promoted to functions : $f^i( \vec e_j) = \delta ^i_j$
So, you have :
$$w(\vec v) = ( w_1 f^1 +  w_2 f^2)(v^1  \vec e_1 + v^2 \vec e_2) = (w_1.v^1 + w_2 v^2) $$
UPDATE 2
Now, in a finite dimensional space, there is an isomorphism between the vectors space and the dual space of the vector space . Let $\vec w$ be an element of the vector space and $w$ be an element of the dual space of the vector space. This isomorphism is :
$$w(\vec v) = \vec w.\vec v$$
Applying this isomorphism to the generating system, gives an isomorphism between $ \vec f^i$ ("reciprocal basis") and $f^i$ (basis of the dual space):
$$f^i(\vec e_j) = \vec f^i.\vec e_j= \delta^i_j$$
Comment: I update my answer
Comment: Stricly speaking, the isomorphism is valid only for finite dimensional (vector) spaces. The dual vector space is a more general formalism, and it is ofen used in differential geometry, too. So try to use it and become familiar with it, because it will be useful to you in the future.
Comment: Thank you for your attention. You explain the first approach as I mentioned in my question. But the latter approach as I mentioned tells us covariant vectors are elements of dual vector space that is linear functions from vector space to scalar field (called functional). In fact my qestion is how two approaches are equivalent.
Comment: Thank you for updating. But one question remains: To obtain covariant component of a vector we shouldconstruct base which are orthogonal to original bases. We can do that by constructing reciprocal bases in our vector space and I think it is non necessary to extract such bases from the dual of the vector space, and decompose the vector on those bases. Can you help me, more ?
Comment: "Reciprocal basis" and "Basis from the dual of the vector" space are the "same thing". More precisely, there is an isomorphism. See my UPDATE 2 in the answer.
Comment: Ok. If they are the same things, why do we deal with the bases from dual vector space ? If our vector space is enough to construct reciprocal basis, why should we refer to dual vector space ?
Comment: As I said before, there is an isomorphism. Isomorphism means that the two points of view are equivalent. So you may adopt the "reciprocal basis" point of view : $\vec f^j.\vec e_i= \delta^j_i$, or the dual vector space point of view : $ f^j(\vec e_i)= \delta^j_i$.
Comment: Ok. I got it. So can we conclude that to introduce covariance concept, we need not refer to dual space and our vector space is enough ?


Let the utility function $U = a + b \min\{x,y\}$. Are $x$ and $y$ perfect complements?

Question: It is possible to have a monotonic transformation on this type of utility function, but what about $a$ and $b$? Usually a function with perfect complements is $U(x_1, x_2) = \min \{a x_1, b x_2 \}$
Answer: Consider a typical car, which is made of one car-body (for lack of a better word) and four tires. Let $x_1$ denote the number of car-bodies and $x_2$ denote the number of tires. Most consumers would prefer cars in the form of one car-body with four tires, and not in any other combinations. So we may represent their preference as
$$U(x_1,x_2)=\min\{4x_1,x_2\}.\tag{1}$$
Thus two cars are preferred to one car can be expressed as
$$
(2,8)\succ(1,4)\quad\Leftrightarrow\quad U(2,8)=8>4=U(1,4). \tag{2}
$$
One car with two extra tires does not increase one's utility:
$$
(1,4)\sim(1,6)\quad\Leftrightarrow\quad U(1,4)=4=4=U(1,6).  \tag{3}
$$
Equation $(1)$ is the utility function associated with a perfect complement preference. In particular, it is a special case of the general form $\min\{ax_1,bx_2\}$ where $a=4$ and $b=1$.
Let's now apply an affine positive transformation to $U(x_1,x_2)$. To avoid notational confusion, let's use $\alpha\in\mathbb R$ and $\beta>0$ as the parameters:
$$
V(x_1,x_2)=\alpha+\beta U(x_1,x_2).
$$
For concreteness, suppose $\alpha=1$ and $\beta=0.5$. And we can verify that the preference illustrated in $(2)$ and $(3)$ is preserved:
$$
(2,8)\succ(1,4)\quad\Leftrightarrow\quad V(2,8)=5>3=V(1,4).
$$
$$
(1,4)\sim(1,6)\quad\Leftrightarrow\quad V(1,4)=3=3=V(1,6).
$$
Therefore, while $\min\{ax_1,bx_2\}$ represents some perfect complement preference, its monotonic transformation, $\alpha+\beta\min\{ax_1,bx_2\}$, also represents the same preference.
Answer: I do not understand your query about "what about $a$ and $b$?"
The answer to your question at large is yes. Utility functions represent the same preferences when monotonically transformed. That is,

If $u(x)$ represents $\succcurlyeq$ on $X$, for $x \in X$, then for any strictly increasing function $f: \mathbb{R} \rightarrow \mathbb{R}$, then the function $v(x) = f(u(x))$ also represents $\succcurlyeq$.

You can try generalizing this result for more dimensions or whatever. It should be easy to apply this result to your utility function in question.


Multipoint routing logistics software solution?

Question: I work for a state health program and am looking for the most efficient way to route inspectors from restaurant to restaurant. This is something like the travelling salesman problem, but with additional complexities. We have 75 inspectors, making less than 8 hour round trips from 17 different offices, inspecting ~18,000 businesses at 1.25 hours an inspection (not counting travel time). These businesses either need inspected annually, 3 times a year, or 5 times a year depending on their assigned risk level. Does anyone have any ideas/suggestions for this? I am talking to Telogis and Viamente as far as getting quotes for using their products but am interested in looking into all avenues. It's possible this is not on the right Stackexchange, if you know of a more appropriate venue I'd appreciate knowing that as well.
Comment: Are you looking for open source as well as commercial based? http://gis.stackexchange.com/questions/210/alternatives-to-pgrouting
Comment: Well currently we have money but almost no IT department so I guess I'm looking for something with good tech support, which to mean would mean commercial, as we don't have anyone with the skills/time to devote to coding/developing a system.
Answer: jsprit can solve your problem. It is a java based, open source toolkit for solving rich traveling salesman (TSP) and vehicle routing problems (VRP). Rich means here that you can model an arbitrary number of constraints that account for your business requirements such as skills, time-windows etc..
And in conjunction with jsprit, you can use GraphHopper.
Comment: [jsprit](http://jsprit.github.io/) is also embedded into an open source (i.e. free) Excel-compatible desktop app [ODL Studio](http://www.opendoorlogistics.com/), so you don't need to do any programming to use it. (Disclaimer - I'm the author of the UI). See our [youtube channel](https://www.youtube.com/user/OpenDoorLogistics) for training videos.
Answer: Our FleetEngine software can also handle such tasks, although you would have to break the problem into smaller tasks, to handle it efficiently.
Comment: I'll have to look into that, I also have been talking to a couple vendors, I am thinking about going with Telogis for a solution right now as they are the only company that could also handle the division of labor into groups, as you mention.
Answer: If you do not have a problem with Java code you could have a look into my Open Source GraphHopper project.
Comment: Graphhopper seem to be about A-to-B routing. Not what the question is about.
Comment: @UffeKousgaard Probably I've expressed myself not clear enough. With 'Java code' I meant dig into some code. GraphHopper is a library so you can implement and tweak what you want. The only missing part is the optimization of the order of the points ("TSP") which is easily implemented ...
Comment: The problem is much more complex than TSP. And you don't even have TSP implemented.
Comment: @UffeKousgaard please explain. And I did not claim that I've this implemented
Comment: Then why did you reply? You are suggesting Dylan to look at your "wheel", when it is a "car" he is asking for. Your library is simply miles away from being able to solve Dylans problem. And it is not just a matter of tweaking as you call it.
Comment: Would you mind to explain what exactly is missing? I would like to get a better understanding of the difference of your car and my wheel. I also don't see that one can live with a application which is not tweakable in this field of logistics. My post wasn't meant to waste anyones time.
Comment: All is missing. If you read scientific articles about logistics (VRP), they all assume distances between customers are either given by coordinates & Pythagoras or a distance-matrix as part of the input. Your "wheel" isn't even part of the "car".
Answer: I have been using RouteSmart for some time, and recommend it highly. It's specifically designed to solve "high density" routing problems (~20K points is something I would refer to as dense), i.e., those involving a very large number of points that must be serviced regularly. It is not an open-source product but imho worth investing to.


Cooking Porridge in steam oven

Question: Can anyone tell me if it is possible to cook porridge in a steam oven?  We're not fond of porridge in the microwave, and, as we never have much time in the morning, we are not able to cook porridge on the stove and allow it to cool for our toddler. I was thinking of trying it in the steam oven with the timer to cook an hour or so before we get up.
Comment: I'm not entirely sure what a steam oven is, but you can certainly cook porridge in a gas or electric oven. You can also pre-cook porridge the night before and rewarm it in the microwave.
Comment: @JenPen Microwave ovens make the best porridge, what is going wrong with that?
Answer: I'm not sure what a steam oven is either, but I think I can answer: YES!
I regularly cook porridge in an unsealed/unlocked pressure cooker that has been set on a hotplate which is plugged into an appliance timer.  I put my oats and liquid into a metal canister that fits inside my pressure cooker, and I put foil on top of the canister to keep extra water from dripping into it.  The pressure cooker has a "rack" in it to keep the canister off the bottom of the pot, which keeps the porridge from burning on the bottom, no matter how high you turn up the heat.
I keep the hotplate set to just barely a boil, because I use 100% milk for my liquid and don't want it to scald.
I have the timer set to start cooking it a full 3 or 4 hours before we wake up.  I prefer to soak my grains overnight, so I set everything up the night before, and we just wake up and eat!

Cooking Porridge in steam oven


12V but what Ampere?

Question: So if my arduino will draw around 800mA @5V and the dc-dc buck converter around 266mA @5V plus solenoid 1.2A @12V, is it a good idea to get 12V 4A (48W) power supply? Since Filip Franik told me that it is a good practice to get 2 times the current I need just in case. Then what will happen to the current that are no in use?
Comment: do not use the arduino as a power supply ... it tends to become an expensive fuse
Comment: Good practice is to calculate your needs and multiply them by 2 "just in case" So if you need 1.5A find a power supply that has a 3A max.a So you will need one that's around 36W (3A * 12V)
Comment: I am using arduino for relay module, lcd, buzzer and keypad. Not using it as a power supply, I am trying to make the 12V the power supply for solenoid and arduino.
Answer: So you want to use the 5V voltage regulator on the Arduino serve as the supply for your 5V components, and feed the 5V regulator from the 12V supply that powers your solenoid?
The problem with that plan is heat. The voltage regulator on the Arduino is a poorly heat-sinked (heat-sunk?) "linear" regulator. A linear voltage regulator is basically a solid state circuit that converts excess voltage to heat.
The higher the supply voltage you provide to the voltage regulator, the more heat it generates for a given current load.
If you feed 12V into the Arduino's voltage regulator, it needs to reduce the voltage from 12V to 5V. 12V - 5V is 7V. So it will convert 7V to heat. You're only drawing ≈220 mA. Total power that will be converted to heat is 7V*0.22A, or around 1.54 watts of power. You should budget for at least 50% more current than you think you'll need, so lets use 330 mA. 7.0*0.33 is about 2.3 watts.
From a little research I did, it sounds like a typical Arduino voltage regulator can dissipate around 1 watt of heat. You're well over that limit even at your low ≈220mA number, so you need a solution that won't overheat your Arduino's voltage regulator.
If you were to instead supply the Arduino's voltage regulator with 7.5V, it would have a lot less work to do. That's a voltage drop of 2.5V. So for a 0.33 max current draw, that would be 2.5*0.33, or about 0.83 watts. That would be under the 1 watt ceiling. However, it sounds like your project is based on a 12V supply.
You could instead use an external switching voltage regulator to reduce 12V to 5V. (search for "boost voltage regulator".) Those are much more efficient, and don't generate nearly as much heat. You could then feed regulated 5V directly into the USB input on your Arduino, as well as supplying it to your other 5V components.
Comment: I have decided to choose the 12V 1.5A (18W) supply connected to 12V 1.2A solenoid and a DC-DC Step Down Buck Converter, stepping down from 12V to 7V, that will cause the current to increase from 1.5A to 2.5A for the Arduino.
AMS1117 5.0V SMD device (0.8A Adjustable/Fixed Low Dropout Linear Regulator) Max Input Voltage is 18V, Current limit is around 1.5A - 1.6A,

My current is around 2.5A minus off 1.5A, what will happen to the 1A?
Comment: I read a article, it says since there is no maximum current rating for the power supply connected to Arduino, the Arduino will draw as much current as it needs (and the voltage regulator can cope with). So its fine?
Comment: I don't understand what you are describing.
Comment: I totally forgot about DC-DC Step Down Buck Converter Output Current: Rated current 2A, maximum 3A (Additional heat sink is required). So from what I currently know buck converter will not create 2.5A just like that.
Comment: I am describing about the the ampere since buck converter steps down voltage (while stepping up current) from its input (supply) to its output (load).
Comment: Your various comments are VERY hard to follow. Please edit your question to state clearly what you plan to do. What you SHOULD do is to drive the 12V solenoid directly from the 12V supply. Then feed 12V into your buck converter, which is rated for up to 2A. I'm assuming you have selected a buck converter with a 5V output. you'd then feed that 5V into the USB port on your Arduino, along with using it to supply your other 5V components. The buck converter will only draw a very small amount of current from the 12V supply, and will not generate much heat at all.
Answer: If my supply increase from 12V 1.5A to 4A. My arduino will draw around 800mA @5V (571mA @7V) plus solenoid 1.2A @12V, is it a good idea to get 12V 4A (48W) power supply? Since Filip Franik told me that it is a good practice to get 2 times the current I need just in case.
I know there is the efficiency of the converter is calculated by dividing the output power (Pout) by its input power (Pin) and then times the input current to get output current.
So for example 7V divide 12V is around 58.3% x 4A = 2.33A. Even if the solenoid takes 1.2A @12V, the current left is 2.8A, so the current is 1.63A, @ 7V. If arduino current draw what it needs and as long as it doesn't draw more than 2A, I think it is sufficient and safe.

12V but what Ampere?


Skyrim NPCs are attacking me for no reason

Question: I need to go to Riverwood for a quest but every time I show up the NPCs start wildly attacking me (including ones with the little icon over them indicating they need to be interacted with). I don't know what to do. Please advise. I am on PS4 and not using mods, if that helps.
Comment: are you a vampire by any chance
Comment: Related, possible duplicate of: [Alvor keeps trying to kill me, can't advance the story](https://gaming.stackexchange.com/q/39776/4797)
Answer: I know of two possibilities:

You commit crimes against them, this can be checked by opening your journal and under "Crimes" tab check your bounty in Whiterun which Riverwood is under. If you have any bounty then it is possible that you have committed crimes against them. This can be cleared by surrendering to any Whiterun guards and serving you jail term or a few other means.
You are a Starving Vampire, vampirism is split into four stages of hunger. By the time you reach the last stage and is starving for blood normally friendly NPCs will attack you on sight. This can be cleared by fleeing out of sight of NPCs and feeding. If you want to avoid getting a bounty for feeding you can consider feeding on bandits instead.
Comment: How do I surrender to the guards? They just attack me when they see me, and then when I die I go back to the save where they are already mad.
Comment: You need to sheath your weapon (have it NOT drawn) and try talking to them or go to the thieve's guild and see if they will help you clear your bounty (you must be a member to do this).
Comment: I am quite sure the other question I linked in my answer explained in details how to clear your bounty. You should read it and maybe one of the other solutions may suit you more. More importantly, only guards arrests, if it is just aggressive citizens they will not attempt to arrest even if you yield. They will only cease aggressiveness if you committed a petty crime.
Comment: While vampirism, crime and one daedric prince mask can be reasons to put a bounty on your head I'm getting a lot of it with this 10th-anniversary edition. I'm suspicious of its lots of new horses. It started after I got all and bandits starting to attack my horses. I'm suspicious of bad faction setup. See my answer
Answer: Old question, but I think I have an answer on how to fix.
The same thing happened to me: I traveled back to Riverwood and everyone in the entire town wanted to attack me on sight. The guards were also making off comments about how I smelled like I was robbing graves, etc. I am neither a vampire nor a werewolf. I have no bounty in the Whiterun hold. The only thing I could think of is that a bug caused some internal flag to be erroneously set that told the game I was a criminal. If this was the case then I'd have to find a way to somehow trick the game into resetting that flag.
So I killed a chicken on purpose in front of a guard. As soon as the guard approached with the usual "hey stop right there" dialog, everyone in the town sheathed their weapons and went about their business. I paid my fine, spend the night in jail, and was able to return to Riverwood without further incident.
Answer: According to this site, in the Bugs section, a few select NPCs will attack you for no reason. Namely Delphine, Sigrid, Alvor, Gerdur, and Faendal will attack. This is said to be due to a thief being in town when you arrive. Surrendering to a guard should fix this.
To surrender, sheath your weapon and try talking to them. Holding block should help if they won't talk normally.
Comment: This is happening with everyone you listed. I can't surrender to a guard as typically they are also angry and continue to attack no matter what.
Comment: If you can, try to find a scroll or spell of Calm and try it on a guard, then talk to them. This should help. If not, simply avoid Riverwood, reload a save BEFORE they was angry, or, if you you could find a mod that somehow cures the issue (in which unless the first two options work I HIGHLY recommend do not do).
Answer: Did you steal anything and then run away? What happens if you surrender? Drop all your valuable stuff and just go to jail. If that doesn't help then it's definitely some kind of a glitch though, maybe someone here can help more.
Comment: How to I surrender? They just keep attacking I don't know how to surrender.
Comment: @Charzzart if memory serves, if you block and try to talk you can surrender so long as your bounty isn't insane
Answer: It's not always because you committed a crime or are a vampire. Sometimes Skyrim just bugs out. Just today I had NPCs at the whole Solitude Dock agro towards me for no reason. It was my first visit there.
I quickly used the console to teleport to Whiterun, wait a few days (in-game of course) and went back to Solitude Docks. Things went back to normal.
Also, sometimes NPCs from mods have bad faction settings. That can also cause this.
Answer: The root cause is usually a hidden faction that has been added to the player. Only NPCs that are flagged as "Aggressive" will attack you on sight when that happens. Riverwood has a number of those NPCs: Faendal, Gerdur, Alvor, Delphine... Elrindir in the Drunken Huntsman is another in Whiterun. All of these NPCs are flagged as Aggressive.
A quick test to see if your factions are the problem

Load a save from before the NPC has been aggro'd, before they show up as a red blip on your compass and draw their weapon.
In the developer console type Player.RemoveFromAllFactions.
Walk close enough where the NPC can see you. If they don't attack, that means one of their factions had a negative view of one of your factions.
Before you do anything else, load back to your previous save. Removing all of your factions is just a test, next we want to isolate which faction is the actual problem.

Isolating the problematic faction
We are going to remove factions from the player one by one until this issue goes away. You can do this using the RemoveFac FactionID command. Some tips to make this easy:

You can pull up the player's list of factions in the left hand pane of the console. Select a faction to reveal its FactionID.
I recommend scrutinizing the list for any that seem like they could be a problem. Start by removing those factions first.
You can test if an NPC is still hostile without exiting the console. Type NPCRefID.GetShouldAttack Player and the console will respond with a number. If that number is greater than 0 they are still hostile and will attack you on sight. You should try running another RemoveFac command.
Once GetShouldAttack responds 0, load back to before you started removing factions. Run that last RemoveFac command (Press Up Arrow twice then Enter), and try running GetShouldAttack again. If it responds 0, then only one of your factions was a problem. If it says > 0, then you had multiple factions added to you that should likely not be present. You need to once again remove them one by one, to isolate which of the other factions you removed that was also a problem.
Use common sense when permanently removing a faction. If it is a faction it seems like you should be a part of, then you have to decide whether to permanently remove it. You can still remove any faction temporarily to test. But whether you continue playing with it removed is up to your good judgement.

For me it was the Wolf faction. It had been temporarily added by a random mod, and then a bug in the mod caused it to never be removed. This faction aggravated the aggressive NPCs in Riverwood, while the rest of the town was fine with me being a wolf. So long as I did not attack the unaggressive NPCs or their allies, they would not attack me. Obviously I should not permanently be part of the Wolf faction. Once removed I could play the rest of my game without issue.
How to see if an NPC is marked as aggressive
Use the developer console (press ~). Select the NPC either, using your mouse or with the command prid. Now type GetAV Aggression and you should get a response like this:
GetActorValue: Aggression >> 1.00
A value of 0, which is what most town NPCs have, means they will not attack unless provoked. Any value greater than 0 means they will attack the player if they don't like every one of your factions. 1 means they are an Aggressive NPC, 2 means Very Aggressive, and 3 means they are Frenzied into attacking everyone on sight.
Using SetActorValue Aggression 0 is a bad idea
You can run SetAV Aggression 0 to "fix" a single NPC. But this is a bad idea, on rare occasion it can break quests that rely on that NPC to be aggressive. Their aggression was set for a reason. This command is permanently altering the NPCs behavioral AI. Ideally we will get to the source of the bug rather than making a modification that can potentially break future quests. Plus, you would have to repeat that command for each aggressive NPC. Instead follow the above steps to find the problematic faction. And if applicable, remove it from the player. This will fix your issue with all aggressive NPCs, rather than just the one.
Answer: This problem is not limited to Riverwood.  You can probably work-around this and similar "why do all the NPCs hate me now" problems by traveling into the wilderness, or at least away from the cell where the NPCs are attacking the player, and waiting or sleeping for 24 hours.  My experience has been that peace will be restored and you can carry on with your stay in the formerly hostile location.
Answer: There are some items that my cause this as well. For example the "Grey cowl of Nocturnal" has several good effects but also cause guards to turn on you. So keep in mind what gear you wear in what areas.
Comment: This is only from a Creation Club pack.
Answer: This happened to me today on my replay of this game.
I was wearing the grey cowl and was attacked, so I went back to my last save and took it off. However, when I returned ,I saw the guards running around attacking and found out there was a thief in town, like what happens often in Riften. So I helped them kill him and took his stuff, and they didn't attack me.
So wearing the cowl makes them think you are his accomplice.
Comment: This has already been mentioned in a [previous answer here](https://gaming.stackexchange.com/a/392283/4797) and does not add to that answer. As per the [Help Center on what answers are deleted](/help/deleted-answers) and the meta post, [How do we handle duplicate answers?](//meta.arqade.com/q/4971/4797) - this answer could be deleted.
Answer: Old question but those days I come back to Tamriel to play the 10th-anniversary edition and it happened a few times with me.
Elrindir - RefId <1A681> Wood Elf fletcher owner of The Drunken Huntsman in Whiterun.
Talsgar the Wanderer - RefId dynamically generated.
And now at Riverwood. So I found this post and guess it's worth sharing what worked for me.
First, it's a legit bug, no bounty/vampirism/etc related aggro.
player.SCAONACTOR - Stops all fights, but once an NPC attacks you, guards will aggro you or him/her.
TCAI - NPCs stop acting, but still can aggro you as you approach, used to stop NPC attacks, and guards aggro.
PRID  - Same as opening the console and clicking on the NPC, to find any id goto:
https://en.uesp.net/wiki/Skyrim:Skyrim
ENABLE/DISABLE - Reboots the NPC, him/her will be moved to him/her initial position.
Finally, I made a video showing the bug happening at Riverwood and how the solution works.


Could light transmittance be used to timely determine extraction?

Question: I was wondering if I could get perfect extraction timing by measuring the light transmittance (of course with the same coarseness of grind) like a Beer's law sort of thing. Anyone have any readings? Or like a method you use to determine optimal extraction?
Answer: Refractometers are widely used to measure the opaqueness of the coffee during brewing to timely determine the extraction time.
Spectrophotometers are used to measure color instead of opaqueness. They are mostly useful to determine the roast degree.
So, why not?
However, in my opinion, perfect is something defined by personal preference when considered with coffee.
If you want to find the perfect roast degree, you may choose your specific beans first, specific brewing method, etc. Then choose the specific roast degree. After that, a spectrophotometer may help you to find that exact point each time you repeat the roasting process. Similar to that, during brewing, a refractometer may help you to find that previously decided specific point each time you repeat that brewing process.
In summary, there is no guidance you can hear as the perfect point that you can scientifically lean on. But you may hear some advice based on the coffee community's common experience. Generally, if you are not into industrial production, you don't generally need nerdy equipment to follow such advise.
Comment: But nerdy = fun.... ;-)
Answer: I know it's down a different line (I like the idea of using light though) but the most common way to test proper extraction is to perform a TDS (Total Dissolved Solids) test. This is the industry standard.
https://tylercipriani.com/coffee-extract/
http://www.tdsmeter.com/what-is?id=0010
I don't believe handheld meters to be too expensive but not sure.


Losing privilege with points lost in setting bounties

Question: Is it appropriate for users to lose privileges with handing out bounties? I've recently posted a bounty worth 400 points and consequently lost even the simple privilege of commenting everywhere. I think this drawback is uncalled for, and suggest that privileges are unaffected by points lost with bounties.
Answer: This is how it has always worked.
If there were no cost to a bounty, then everyone would post one, and they would lose part of their essential value as motivators.
Comment: But if privileges signify the trust of community in a user, why would posting bounties reduce the trust the community places in the user?
Comment: I think that it should be as such: You don't lose your current privileges, but you are farther from new ones.
Comment: @Oxwivi I see it more as, "I want an answer to this question so badly I am willing to give up this privilege in exchange." That said, I would definitely advise users to avoid going below 100 reputation. http://askubuntu.com/privileges
Comment: I don't know - even if someone wants answers bad enough to give up privileges, there should be a limit to how much privileges one can lose...


May I place a towel on the food that's on the platta on Shabbos?

Question: This is a hatmana (insulation) question. I want to know if there is an issue with putting food on the platta on Shabbos day and then putting a thick towel ontop of that food in order for the food to heat up faster and get hotter?
Answer: You have three problems here:

Hatmanah on Shabbat itself
Mosif hevel -- adding heat
Hatmanah while it's on the plata (if that's what you're asking about)

All three of those issues make it assur (forbidden). [Shmirat Shabbat C'hilchata 1:65].
However, you can get around problems #1 and #3, as illustrated in the next paragraph.
Hatmanah is only a problem if you cover the entire pot. However, if your cover does not touch the entire thing, it's OK to do even lechatchila (initially) and while it's on the plata. It seems though that you'll have to use something that does not add heat.
Mosif hevel seems to be a problem even when it is fully cooked (see http://vbm-torah.org/archive/cookshabbat/22cookshabbat.htm, quoting Rav Auerbach).
CYLOR before acting on advice given in this answer.
Comment: If you drape the towel over all of them, per force it is not touching the entire body of any pot.
Comment: @hazoriz "actual hatmana with a davar she-mosif hevel, and one may not be lenient even about that which is fully cooked. " -- http://vbm-torah.org/archive/cookshabbat/22cookshabbat.htm, quoting Rav Auerbach.
Comment: About covering the entire pot... I wonder if there are a bunch of dishes on the platta and I drape a towel over all of them but leave one of them slightly uncovered, would that help with the rest of them in taking care of issue's #1 and #3?
Comment: Wouldn't that depend on why not having the whole pot covered would be OK? If it's a demonstration that you are not concerned with insulating the pot (I vaguely remember this being the position of a Rishon) then maybe in this case it would not help since it's clear that I'm draping the towel for insulation purposes? Just thinking here...
Comment: isn't moisif hevel only a problem when not yet fully cooked?


Did the treaty of Versailles require closure of German cadet schools?

Question: I'm hoping someone can give me a definitive answer about whether German military schools/academies ("kadettenanstalt" - secondary school level) were forced to close by the Treaty of Versailles. It seems I once read this somewhere.
Answer: Yep.
Part V, Article 176 of the treaty covers closing military schools. Germany was allowed one school per arm of the military:

On the expiration of two months from the coming into force of the present Treaty there must only exist in Germany the number of military schools which is absolutely indispensable for the recruitment of the officers of the units allowed. These schools will be exclusively intended for the recruitment of officers of each arm, in the proportion of one school per arm.

This allowed only three schools to remain, as they (presumably) had three military arms at the time. As explained in the rest of the treaty article, all other military-related schools needed to close:

Consequently, and during the period fixed above, all military academies or similar institutions in Germany, as well as the different military schools for officers, student officers (Aspiranten), cadets, non-commissioned officers or student non-commissioned officers (Aspiranten), other than the schools above provided for, will be abolished.
Comment: Nice answer, although it would be good if you provided the source for your last quote.
Comment: @SJuan76: The last quote was simply more of the linked treaty article, and I updated the answer updated for clarity.
Comment: Accepted as correct.


What is the best transmitter/receiver to use with an Arduino RC?

Question: I want to customize an RC car that I have because the controller is gone. I'm going to use an Arduino with a custom motor controller but I have no idea what to use for the transmitter/receiver. I've seen some IR sensors being used but I want something that uses a frequency channel. Has anyone had experience doing this? What is the easiest way to go about accomplishing a remote controlled Arduino car?
Answer: That depends largely what is controlling it
Some options include:

wifi, if you have an expansion board, from a PC or phone (spec says: 66ft/20m)
bluetooth works great, directly from your phone (spec says: 32ft/10m - 320ft/100m)
433mhz ASK transmitter/receiver from another Arduino or other hand-designed circuit (spec says: 100m/320ft)
Infrared receiver - from a TV remote! (range unknown, depends on remote & conditions; would not trust it 10m outside without testing).
Cellphone network - longest range (nationwide!). If you get a cheap android to do some of the work, you can use the phone's compass & gps & extra processing power, as well as the camera(s)!
Remote control. I know you said you lost yours, but in case someone else is looking here, you can hook up an rc receiver to an Arduino fairly easily. https://www.sparkfun.com/tutorials/348 for more info.

Many of these ranges specified will depend on the antenna. If your car can tell it's lost signal, then it can stop; otherwise you have to outrun it, or wait for it to hit a wall.
Edited to include cellphone network, and added ranges to options
Answer: Here is a link to a pair of Arduino compatible wireless transceivers. One of the listed applications in the description is "remote control systems such as RC vehicles," so I think this product would suit your project well.
According to the reviews / answers to questions on Amazon, the transceivers have an reliable range of just around 120 feet, so this component would be entirely appropriate in a remote-controlled build.
Comment: You need two arduinos for this, and 120 feet isn't very far, but thanks. +1


Missing Property and Cash

Question: I bought one of the cash cards from the xbox store which gave me about $1.25m in-game cash for roughly £13.50 directly from my linked bank account card. Then I went and purchased the most expensive property in the game, which was $400k from the money I just bought from the store. I used the property whilst I played for a couple of hours before saving the game twice (just to make sure it did) leaving the game and switching off my xbox. A few hours afterwards, I went back online to find that the property was gone and appearing as if it was never purchased, but the $400k wasn't there either! So basically, money from my bank has gone towards downloading some in-game cash that has partially disappeared. I've sent rockstar a message but there isn't any sign of a reply. I feel like I've been robbed - it's frustrating. Any form (info/advice/updates/etc) of help would be appreciated!
Comment: I've experienced similar losses.  Thankfully, only with in game earned cash.  I'm hoping that the various servers are just slow to sync up right not and I'll log on in a few days and all the cash will be restored.  I've submitted an issue to Rockstar about it.  Still waiting to hear back.
Answer: Online is pretty buggy right now, it's entirely possible that what you experienced is one of these bugs.
http://www.computerandvideogames.com/431870/rockstar-working-around-the-clock-to-resolve-gta-v-online-problems-errors-and-bugs/
Comment: Same thing happened to me but instead i lost all 1.25 million from my bank. support staff at rockstar only replied once for me but we will probably get our in game cash back once the server issues are resolved i hope.
Comment: I also lost the 400k property. I purchased it from the in game website. It was available, but upon joining my friend's session it was no longer in my possession. It shows on my stat sheet that I spent 400k on properties, so there is an electronic record of it in the system. I imagine Rockstar will rectify these issues, I hope.

Missing Property and Cash


What is a multipoint shapefile?

Question: What is the difference between a multipoint shapefile and a point shapefile. in the creation of a shapefile In ArcGIS it has the choice of point shapefile and multipoint shapefile. But I do not know what their difference.
Answer: Shapefiles support four fundamental data types: Point, Polyline, Polygon,  and Multipoint. Points are simple {X,Y} features. Polylines are ordered sets of points, and Polygons are the areas encompassed by closed simple lines. Polylines and Polygons can be multi-part to model discontinuous features, like a surface street separated by a highway, or a collection of islands.
In the shapefile model, Points can't be multi-part, but there is a distinct Multipoint type to take that role. The difference has to do with the envelope in the data record needed for Multipoint shapes and the different approach to spatial indexing of point and multipoint objects.
Multipoints are an obscure representation option for most point-ish features, but they can be used to optimize the display of large numbers of points. I had a dataset involving  tens of millions of features covering the globe, and I was able to successfully draw a hundred thousand features within a single one degree square with subsecond timing by unioning the points into multipoints to reduce the number of features rendered for each tile.
Note that shapefiles don't support anything like a geometry collection, only permtting the specified shape type or a null shape (zero vertices) within one file, so if both single and multi-part point shapes are required, the single-part points will be stored as degenerate Multipoints (with a point count of one, and an "envelope" with the lower-left and upper-right corners coincident with the point itself).This is less efficient in storage (52 btyes vice 16) and the spatial index is not as efficient, either, so if you'll only have single-part points, you should use the Point datatype.
Comment: You could implent a pointcluster with a multipoint geometry,  but I wouldn't say they were equivalent. Multipoint is more of an abstract datatype.
Comment: would it be fair to say multipoint shapefile is similar to clustering?
Comment: Saying that "Points can't be multi-part" is fairly absolute. Functionally, points are considered multi-part when the are grouped by their attributes. I really don't care for multi-part classes for the work I do but, I imagine that there are certain GIS sectors that find them very useful. That aside, I find ESRI's handling of lidar point clouds using multi-part geometry absolutely useless.
Comment: A **point** can't be multi-part, by definition. After having been grouped, they are **multipoints**, some of which might be degenerate.
Answer: Take a look on, how the geometry is related to the Dbase file records.
If you have a point shapefile, each point is related to one record.
If you have a multipoint shapefile,  a set of points is related to one record.

What is a multipoint shapefile?


how to make this but for pictures instead of videos?

Question: I found this nice video about showing subjects focused and the background blurred or viceversa
http://www.youtube.com/watch?v=h7wa-pd6PJU
However, its for video only, the question is how to make it for pictures?
Answer: You can manually focus to the foreground using an aperture like f/2.8 or wider. That will create the in focus subject and blurred background. It depends on what camera and lens you are using to do this.
You can use a 'Lightfield' camera like the Lytro which lets you take a photo with multiple layers of depth.
There are some very clever 'hacks' to make similar photos by filming static scenes with DSLRs and adjustable focus however this is tricky and obviously doesn't work for moving scenes.
See this question and this question for more info on achieving this effect.
You'll have to be more specific with what you want if you want more detailed answers than that though i'm afraid.
This might also help for manual focus in the Nikon P510

You can't select the focusing mode from the side zoom, only vary it in
  the MF mode; so you should always select the focusing mode from the
  selector (flower icon); for example, if you have selected MF for P
  mode, when you start again the camera or go into shooting mode the P
  and MF appears left side up the display; you press OK and the focusing
  vertical gauge appears on the right side; now you can go up and down
  it from the side zoom if you have selected MF for it from the menu.
  For me it's quite enough, because I wanted all the time directly use
  the selector, thus actually trying to set the flash (up) or to select
  another focusing mode (down).

Source: Here
Comment: Its a fascinating device to me, although practically its probably not the most useful tool (or cheap) i'd personally love to see it incorporated into larger formats and more diverse lenses. I often take a shot where the focus is just a little off and i don't notice at the time because i'm to busy shooting and the cursory review looks fine on the 3" screen. More than once i'm sure it'd be of benefit to be able to select the focus after the fact :)
Comment: the most incredible part is that one does not need to focus it to take a picture!
Comment: I am using a Nikon P510
Comment: @LuisValenciaMunoz okay cool, what effect do you want exactly?
Comment: blur background, focus on a close subject. 1 or 2 meters.
Answer: By referring to "subjects focused and background blurred or viceversa", I believe you are looking for the effect produced by a shallow depth of field.
Large aperture lenses will give you this effect very strongly, but you can probably still achieve it (albeit to a smaller degree) with the lenses you may already have.
The easiest way to see this effect is to:
1) zoom to the longer end of your lens if your lens is a zoom
2) set your camera to aperture priority mode (A or Av), if it allows this and dial the aperture to the lowest number on the camera (often something like 6.3, 5.6 or lower)
3) move as close to the subject as your lens will allow you to while still focusing
4) take the picture
This will give you the effect shown here.


Is there a way to hide the masking lines when using Texture Paint with masking enabled?

Question: I'm getting into painting textures onto my models using Blender's texture paint.  I like that Blender provides the 'face selection masking' button that lets me mask out faces that I don't want to accidentally paint.  However, when enabled this feature outlines all the selected faces with bold white lines - making it really difficult to see the results of my painting.  Is there a way to hide this overlay?
Comment: im not sure , but select the faces you dont want to paint and press "H" , and if you want to unhide them press alt - H
Comment: To hide texture borders, I had to disable mipmaps in Blender menu "File" -> "User settings" -> "System". I am not sure if you had the same problem but it may help other people.
Answer: As far as I know there is no such option, which disables the white lines.
In Weight Paint Mode you have an option to display vertices instead of edges, but in Texture Paint Mode there is no option like this.

I think that using the Clipping Border Tool may be a good solution for you. Press ALT+B and drag a mouse to select the portion of the model which you want to be visible.

You can rotate selected portion, and paint on it precisely. And the most important is, there are no lines that may disturb you :).
Answer: Well, just download the latest Blender.
Hiding the masked texture painting lines was one of its features:
Blender 2.73 Release Notes


Is there a place to report overzealous downvoting?

Question: If there was a place to report instances of overzealous downvoting, maybe the admins could initiate some action. Is there such a place?
Comment: Could you provide more detail? What do you mean by "overzealous downvoting"? Post some more relevant information. Thanks. :)
Comment: [_Two_](http://english.stackexchange.com/questions/79498) downvotes is overzealous? On a question where you ask about a _job title_?  Per the FAQ: "Please, don't ask questions about naming, including naming programming variables/classes." I would think the name of a job title could easily fall into that category, and thus make the question subject to downvotes.
Comment: @bagheera: Don't be too "overzealous" in interpreting why a question is closed. When voting for a question to be closed, users are presented with a multiple choice screen, forced to choose between one of five reasons why a question gets closed (you can see a screen shot [HERE](http://i.stack.imgur.com/0u9wl.png)). There is no "Other: please explain" option. So, I mentioned _naming_ in a comment as a possible reason why some may have voted to close, and "too localized" is simply, of the 5 possible reasons, the one that most closely mapped to the reason some saw fit to close it - no zealotry.
Comment: @J.R. Overzealous is not so much about the _number_ of downvotes as it is about the zealousness with which the guidelines are enforced, even on a single down vote. Your interpretation is a case in point. You object saying the question is about _naming_ whereas the person who  closed the question said it is too _localized_. And now, after my protest, someone has deleted the question altogether, thereby implying the question was extremely off topic or very poor quality.
Answer: Yes, there is such a place; this meta site. But before we are overwhelmed by disgruntled questioners, I have to define 'overzealous'.  If one person downvoted a large number of your questions in one day, it's a fair bet that it is unrelated to the quality of your posts; this is 'abusive downvoting', which is banned, and should be reported here if the automatic systems don't catch it.  But if a large number of people downvote one of your questions (remember that they are each sacrificing a point of rep to improve the site, as they see it), that is probably a sign that the question doesn't belong here.  This doesn't mean "You're stupid"; it means that a site to do with English is in constant danger of being diluted to the point of uselessness, so we have strict guidelines about what questions are allowed here.  You haven't put a link to your question, so I'm guessing; but the minimum expected is that the questioner should have: checked the FAQ to see whether it's on-topic: consulted authorities (dictionaries, grammars, Google for usage), and explained how the answers there are insufficient: and put as much effort into framing the question clearly as he expects from an answerer.  If other users of the site think you didn't do this, you will be downvoted, and there is no comeback against commmunity moderation; either improve your posts (improve here meaning make more suitable to EL&U rules), or find another site that suits you better.
Comment: Downvoting questions is free. Downvoting answers is not. :)
Comment: I mean, it's free for the downvoter, of course. The OP will get a -2 rep instead. [Should downvotes on questions be "free"?](http://meta.stackexchange.com/q/90324/176533).
Comment: @alenanno: Really? I feel an episode of question-downvoting coming on :)
Comment: @TimLymington, I know you were half-joking, but please don't do that. I was just looking at some of the new highly-downvoted questions, and not a single one was really that bad. They're not exemplary, certainly, but they don't deserve the vituperation they've received.
Comment: @Marthaª: perhaps quarter-joking (and for the record, I didn't downvote any of them).  But the serious point remains: unlike closevotes, downvotes require no justification, and this is status-by-design.  So (absent abusive voting), any new user with 125 rep (who may not know/care about etiquette) can downvote anything he personally dislikes.  Above a certain level, we can shrug this off (and in the long run sympathy upvotes will probably cancel it out).  But new users will undoubtedly be discouraged: so the more new users we have, the fewer new users we will have.  A most ingenious paradox.
Comment: The [question](http://english.stackexchange.com/questions/79498) in question has since been removed by the powers that be. The question was "Is there a more suitable title for someone who is head of both HR and Finance?" It was downvoted without comment, closed saying too localized and now is removed (upon my protest I believe). The custodians of the OED have a more _inclusive_ attitude towards what counts as English than what the powers that be at english.stackexchange have towards what's an acceptable question here.


classification performance metric for high risk medical decisions

Question: What is the best classification performance metric for risky medical treatments like surgery? for example a patient should NOT suggest a surgery (negative) if he/she can be treated by medicine (positive). Does Negative predictive value (TN/TN+FN) works for this situation?
Answer: Check ROC curve, increase the threshold and measure PPV.
Also you can not use only one in isolation, you have to check sensitivity, specificity and PPV in order to understand the complete scenario.
Answer:
Minimizing false negatives is definitely a good strategy.
You can also generalize to using weighted f-measure. It allows you to give tunable weightage.
Answer: This could be the concept you are looking for:
Cost curves.
The concept is ROC curve but with cost associated for every type of cost.
For example: False negatives have a cost of 100. False positives have a cost of 5. Using cost-associated ROC curves will help you punishing much more FN than FP or viceversa.