Feature selection

Question: There seems to be an obsession in machine learning as well as traditional regression modeling for feature selection.  The majority of analysts do not seem to understand that feature selection is not a required part of modeling and can often stand in opposition to optimal prediction.  How can we better get this general point across?
Comment: I often link to one of these posts [Algorithms for automatic model selection](http://stats.stackexchange.com/q/20836/17230), [Feature selection and cross-validation](http://stats.stackexchange.com/q/27750/17230), [Should covariates that are not statistically significant be 'kept in' when creating a model?](http://stats.stackexchange.com/q/66448/17230).
Comment: @AndreSilva But it's also a Meta issue, in the sense that it's a recurring issue - across *hundreds* of questions.
Comment: Isn't this question suitable for the main site?
Answer: TL;DR: Frank and Scortchi have a point for prediction - but the question Scortchi proposes doesn't really address people's concerns about assessing a variable's relevance. I think this is a pertinent question to which we don't yet have a good answer. Apart from point 9 in gung's answer here, which says that no technique will save the analyst from having to actually think about his data.

I think there may be an unstated philosophical/epistemological/teleological point here: WHY do people actually want to model?
If they want to model for prediction, then things are easier. I fully agree with Frank and Scortchi here.
However, often people model data to "understand a predictor's relevance", to use terms that are not loaded with technical meaning. This usually takes the form of inferential statistics (and can lead to an unhealthy obsession with p-values), but things like variable importance in random forests aim in the same direction. As do formal causal models.
I would say that this is a legitimate aim of data analysis, both in an academic and an applied context. However, understanding a predictor's relevance runs into problems that we don't see if all we aim for is a good overall response prediction.
In this second situation, we could argue for "tapering effect sizes" in the sense of Burnham & Anderson: everything has an impact, it's just that effect sizes taper off to insignificance. This would argue for keeping everything in the model... except for the bias-variance tradeoff (see @Scortchi's suggestion to link to this question) and non-identifiability. So we need some kind of dimension reduction or regularisation.
Unfortunately, dimension reduction mangles predictors beyond recognition, so assessing a variable's relevance after, say, PCA, will be hard. And regularization can introduce an element of arbitrariness that can be hard to defend - if a predictor's relevance depends on your Bayesian priors, this is a weak point in your argumentation. Optimal choice of lasso or elastic net parameters can at least remove this element of arbitrariness, and then we can look at standardized parameter estimates in an elastic net, so this is something I like, although I don't know of any actual research on assessing variable relevance via elastic nets (pointers would be most welcome).
Unfortunately (again), this seems like we would need to push people towards one very specific kind of model: elastic net-based regularization. But what do we answer those people that are using some other kind of model, for whatever reason, and find that it does not work well with the full set of predictors?
Alternatively, we can argue that you only have understood a process well if you can predict it well. So, to assess a variable's importance, build prediction models with and without that variable (and any transforms of the variable you want), test the models out-of-sample, and see whether prediction accuracy goes down. (Diebold-Mariano type tests can be used for disciplines that can't get away from p-values.) This is actually my preferred position.
However, there is the problem that nominally out-of-sample tests actually aren't, because people will run this sequence iteratively in building their models. In addition, it is hard to get an approach like this accepted in disciplines that traditionally don't tick like this, like psychology. Not to speak of the fascinating discussions you can have about how to actually measure a prediction's accuracy, where the arbitrariness discussed above creeps in again.
Comment: Thanks for this thoughtful answer. I wasn't thinking about prediction especially, however. If "assessing a variable's relevance" means making point & interval estimates for coefficients of terms involving it, you don't want to drop it during feature selection, & you don't want the biased estimates got with regularization. (Note that when you've a couple of highly collinear predictors, LASSO's just as flighty in which it excludes as stepwise procedure.) If it means testing how well you can predict with it vs without it, then do just that, as you say. So I wouldn't be pushing people towards ...
Comment: ... elastic net regularization in either case. If someone had a model that didn't work well (wide confidence intervals for coefficient estimates, badly over-fitting) & wanted to make inferences about *all* predictors, I'm not sure what I'd suggest except to get more data. (There might be needles-in-a-haystack type problems where feature selection could help by setting low coefficient estimates to zero - examining its consistency through resampling would be advisable.) But I think this question is more concerned with people who've got perfectly good models that they unfortunately feel they ...
Comment: ... *ought* to muck about with even though they needn't
Answer: One way to communicate feature selection is not a required part of modeling would be to present non-trivial use cases wherein feature selection would be detrimental, despite its utility in the assessment of variable importance as well as interpretation.

Feature selection


AC Compressor issues

Question: My AC Compressor is bad.  I work out of town and I can't afford to have it fixed right now.  Since winter is upon us do I need to have it fixed right away?
Comment: Can you specify how it is bad? Does is not blow cold air? Is it making noise?
Comment: Welcome to Motor Vehicle Maintenance & Repair! Along with what @mikes says, you show it's a Ford Focus, could you also tell us what the year of manufacture is as well as the model?
Comment: Why is it bad? Real concern should come only from a seized compressor that can turn on any moment (to avoid any further manage until the repair can be done, the clutch coil, if the compressor has one, must be disconnected from the harness; a clutchless compressor should instead have already severed its seized shaft from the pulley as a safety measure) or one with a noisy or seized pulley/pulley bearing (must be taken care of as soon as possible).
Answer: A working AC is not a requirement for any time of the year, so you don't have to get it fixed at all. A working AC can be extremely useful for defogging your windshield as it dries the air in your car, even in wintertime, however it is not an essential.
The only time a compressor failure needs to be fixed right away is if the clutch seizes as that will cause excessive belt wear.
Comment: Some cars specifically state to leave a/c on permanently and let the system control what it does, so that pump damage does not occur...
Comment: Sure, @SolarMike, I'd leave mine on most of the time as a matter of course, but if it's broken anyway....
Comment: More precisely, the only time a compressor failure needs to be fixed right away is when the compressor pulley bearing is compromised and begins making grinding or groaning sounds even with AC off. A noisy ball bearing can seize up any moment, and since modern cars have a single serpentine belt a seized accessory pulley means that the alternator, the power steering pump and the water pump stop working too, and this means choosing between a very damaging limp home, a tow truck ride or being left stranded.

AC Compressor issues


The battery is fine but my car will not start not even a clicking sound

Question: When I turn the key in to start all the lights on the dashboard go out completely and when I turn it back to the off position the dash lights back up. What could the problem be if the battery is okay?
Comment: [See my answer here](http://mechanics.stackexchange.com/a/412/85) to make sure the battery is good.
Comment: The lights (and all kinds of other accessories) should go off when you turn the key to "start." This is "load shedding" to make sure that all the battery's capacity is available for the starter and engine electronics.
Comment: If the battery ends up being good, I'd question the ignition switch ..especially in a Chevy. I've been through two different ignition switches in a '97 Blazer.
Comment: What car is this? i have seen this problem on a Jaguar it was caused by a Huge Fuse that was hidden behind the carpets on the back wall of the boot, the fact it's working until high current draw (starting the engine) would say a fuse has / is failing.

Don't for get to start an engine there is a lot of power from bat needed, depending on car Starter Motor, Injectors, Coil pack & more all high power devices.
Answer: Some things to check in order of likelihood-

Check the battery connections are tight.  A loose connection may prevent your car from starting, even when the lights, radio, etc., may seem to be working fine.
The battery may not be fine. Lights are not high load,so having the lights work is not an indicator of how healthy your battery is
Starter motor. Some starter motors stick as the fail, so occasionally a good whack with a piece of wood is required (don't try this if you aren't sure which bit of metal is your starter motor, you might break something)
Fuses. Easy to check all your fuses in the fuse box with a multimeter.
Wiring. If all else checks out, you may need to carry out a full check on your wiring to see where the failure is.
Comment: Based on the description, I'd agree with your first bullet.
Comment: I'd bet money that it's the battery. I've seen a lot of them go out the same way.
Answer: Have the battery load tested. I've had several batteries go dead in the same manner: dash lights working just find until you turn the key and it all dies.
Answer: Make sure all the connections are clean.  Test the battery to ensure it really has 12volts.  Use a voltmeter.
I've had a battery that worked fine, but couldn't start the car because the connections needed cleaning.  Even if there isn't corrosion it could be an issue. Once I had those add-on connectors that go on the end of the battery cable get so rusted it stopped the connection from working.
Answer: The same thing happened with me ( Ford Focus - bad starter? ) when trying to "turn the car over". The current drawn "killed" the car for about 2 minutes, where nothing electrical worked at all.
Check that the battery terminals are clamped down correctly. You might need to remove the clamps and reseat them.
Comment: I've experienced something similar. In my case, I think I was able to wiggle the terminals or something like that to get home. Afterwards, I tightened the terminal nuts and all was good for awhile. I eventually needed some battery service, but I think they just cleaned the terminals, sprayed on the red stuff (some sort of corrosion resistant), and it was good to go.
Comment: Ironically enough, it was the corrosion stuff that messed up the connections... The mechanic used vaseline over the posts, and it seeped in between the post and terminal.
Answer: Make sure battery connections/post are clean and battery has at least 12.4 volts.
Check and make sure wires to your starter are not making ground connection to any metal, and are exposed and not covered to anything metal. Also, could be the starter/alternator.   Process of elimination -- more then likely it's electrical, not the motor. Hope this helps.
Answer: Immobiliser has kicked in cause you removed the battery, got the same problem,  I've been told locking & unlocking the car with the key fob will do it!! Mine don't seem to work, the real answer is a 4 digit code you get when you buy the car from the dealer which I didn't, it not the radio code which is all I had it's the ecu or eka which is in the owners manual under security/safety, you use the code in the car door lock by turning the key whatever number of times one way then opposite way for next & so on, if you find any other way let me know


Irish Cream Liqueur chemistry

Question: Among Irish Cream liqueurs, particularly lower-shelf than the big names, do any use an all-out unrefrigerated-single-serve-coffee-creamer approach to achieving shelf stability, i.e. tetrasodium pyrophosphate and other preservatives? If so, any clues as to which do and which don't? Can assumptions be drawn based on ABV? Price? Other factors?
Comment: Do they not need to list the ingredients?
Comment: In the US it's not required to list ingredients on liquor.
Comment: Ah that makes sense
Answer: Baileys and other Irish Cream manufacturers state that their liqueurs do not need to be refrigerated. As long as they are stored between recommended temperatures of 41ºF/5ºC and 70ºF/21ºC and kept out of direct sunlight, they have a shelf-life of around 2 years.
The alcohol in the product acts as the preservative on its own - so no need to look for anything containing artificial preservatives (in the cases where you can actually  find an ingredients label.)
As far as an "unrefrigerated-single-serve-coffee-creamer" version goes - as with almost all types of alcohol, there are plenty of companies that produce miniature versions of Irish Cream, Baileys included:

Considering that the shelf-life is going to be around 2 years whether the bottle is open or not, the miniature versions are manufactured more for consumer convenience than for shelf-life stability.

Irish Cream Liqueur chemistry


Corey-Schmidt oxidation of primary alcohols

Question: Why does pyridinium dichromate (PDC) in dimethylformamide (DMF) oxidize alcohols to acids while in methylene chloride the oxidation stops at the aldehyde level?
Answer: As stated in the previously posted answer:

This oxidation into
  carboxylic acids succeeds when the intermediate aldehyde equilibrates with a liberal proportion of hydrate; that is, when the intermediate aldehyde belongs to the aliphatic kind and is not highly hindered. The water necessary for the formation of the intermediate aldehyde hydrate may proceed from the decomposition of PDC.$^{[1]}$

Though the text does state that water may form from decomposition of the dichromate anion, since DMF is so hygroscopic as a result of its high polarity ($\epsilon_\mathrm{r}=38^{[2]}$), I would not be surprised to learn that little to no over-oxidation occurs in completely dry DMF under an inert atmosphere.
This is only speculation though, and the dichromate anion may very well be decomposing to produce water in the solution. As such, I will propose a reaction mechanism for this decomposition. The first step can only occur when pyridinium dichromate is well solvated and protons are free to be transferred between the species, which occurs in DMF but not in DCM:
$\hspace{.6cm}$
This produces chromic acid, another chromium(VI) oxidizing agent. Unlike dichromate oxidation, however, chromic acid oxidation actually produces water as a byproduct, which is then free to hydrate the resulting aldehydes:
$\hspace{.8cm}$

$[1]$ Tojo, G.; Fernández Marcos. Oxidation of Alcohols to Aldehydes and Ketones: A Guide to Current Common Practice; Springer: New York, NY, 2006; p 28.
$[2]$ Wikipedia: Solvent
Answer: I attempt to provide an reasonable answer to this question.
The Corey-Schmidt oxidation uses PDC (pyridinium dichromate) to primarily oxidise alcohols to carbonyl groups. PDC exists in the form of stable bright-orange crystals that remain unaltered by manipulation in the open air. Its lack of hydrophylicity facilitate its handling and allows the selective oxidation of alcohols in the presence of very sensitive functional groups.

The medium generally used is $\ce{CH2Cl2}$, ethyl acetate, benzene, methyl cyanide or chloroform. PDC is far more reactive in more polar solvents like water.
Now, coming to your question the interesting thing is that DMF, which is very efficient in dissolving PDC,causes the over-oxidation
of certain alcohols into acids, something that may happen even
in the absence of added water.

This oxidation into carboxylic acids succeeds when the intermediate aldehyde equilibrates with a sizeable proportion of hydrate (when the intermediate aldehyde belongs to the aliphatic kind and is not highly hindered). The water necessary for the formation of the intermediate aldehyde hydrate may proceed from the decomposition of PDC.

So given that, it may be concluded that DMF causes PDC to over-oxidise due to following reasons (possible):

Decomposition of PDC in DMF to form water molecules, so that hydrate formation of intermediate aldehyde occurs and then conversion into carboxylic acid.
This may be aided by the solvation (solubilising) of PDC in DMF.

Reference:
G. Tojo, M. Fernández Oxidation of Alcohols to Aldehydes and Ketones:
A Guide to Current Common Practice; Springer Science+Business Media: New York, 2006.
Comment: I would love to see a mechanism of hydrate formation in the absence of water — especially if you postulate it occuring *via* the dichromate anion.
Comment: With the mechanism I could accept this.
Answer: A reading of the Corey-Schmidt1 paper on the oxidation of non-conjugated primary alcohols and aldehydes to the corresponding carboxylic acids with dipyridinium dichromate (PDC) in dimethylformamide (DMF) makes no explicit mention of drying DMF but flame-dried glassware is employed. Perhaps this implies that the solvent was dried. @Ringo has speculated (Ringo's admission) how water may be generated from PDC in situ to then form the aldehyde hydrate necessary for oxidation. Given the stoichiometry of the reaction (3.5 equiv., PDC/RCH2OH), sufficient but limited water can be produced in this manner. Nonetheless, this pathway is viable. An equally speculative method of "hydration" invokes DMF as an alternative to water. continued

A species akin to hemiacetal 3 (it and other intermediates may be protonated) may add to chromium trioxide 4, or PDC itself, which forms 5 and collapses to a Cr[IV]-species 6 and 7, which is nothing more than a reactive, masked anhydride. The Corey-Schmidt paper experimental section calls for the addition of the reaction mixture to water.
1) E. J. Corey and G. Schmidt, Tetrahedron Letters, 1979, 5, 399.


What happens with two FSA accounts and one accidental expense submitted to each?

Question: What happens if accidentally a husband and wife each submit a specific charge to their respective FSA for reimbursement?
Answer: Search the website. There is generally a way to reverse the charge. I have seen these options exist on both Flexible spending accounts and Health Savings accounts.
If the expense was for last year, and you had other expenses that you did not submit because you reached the limit, you will probably be OK. Send them both information on the wrong submission on the new submission. If you  left money on the table last year, they will want a check from you.
If the expense was for this year, you will not have a problem reversing the charge, because much of the year is left.  Of course due to the new rules regarding roll-over of lat years money into this year it could be more complex.
You want to resolve it as soon a possible to minimize the complexity as deadlines for submission approach.
If you don't report the mistake the extra income from the incorrect submission is considered taxable.


Propensity Modeling for Retail Marketing: Model Adjustments Based on Consumer Life Changes.

Question: I built a predictive model using logistic regression for direct marking creatives. I built a "children's" model which predicts buying behavior for those that purchase boys, girls and baby apparel.  But one may have a high propensity right now to buy baby clothes but in 12 months, when ones  kid is a toddler, their propensity drops for baby and increases for Girls/Boys.  I've been trying to brainstorm ways to take into account that scenario.  My question is, can anyone suggest options for adjustments to the model to based on that additional criteria?
Comment: well have you tried considering the age ranges upon those clothes, items?
Comment: Good point. But i only have the age ranges ( about 30%) of the people that by the clothes - so most likely the parents and not the age ranges of the kind that are where them.
Comment: You don't have info about the product? Like product data descriptions?
Comment: Decision trees model, maybe?
Comment: Ok, Decision tree. Would you find filling me in why that might be more appropriate is this situation
Answer: If you have the purchase data for all these customers, this could be one way to approach the problem:
You could either cluster the customers into natural groups based on their most recent purchases or find association rules (the likelihood of the customer purchasing in a particular category based on their most recent purchases).
I'm not sure how well this approach is going to work for you, but it worked for me in my scenario of propensity scoring. So, if it makes sense, try to relate your data to mine.
I had a list of customers and their purchase behaviors. From those purchase behaviors I deduced association rules to determine which customer is likely to purchase in what product category (based on their previous purchases- associated with the previous purchases of the group).
You can also include recency and frequency of the product purchases into the model to decide whether or not to recommend a particular product/offer to the customer for a specific time.
Based on the confidence, support and lift metrics of those rules for each customer, I mapped them to highly likely to purchase in this category with confidence being their propensity score.
Let me know if this works with your data.


IIS 7.5 delete binding

Question: I am looking for a way to delete range of Host header binding from my IIS,
any idea? There is have some batch script that will know to delete chunk of binding settings?
Answer: There is powershell command to remove them Remove-WebBindings - see http://technet.microsoft.com/en-us/library/ee790591.aspx
This could be used with Get-WebBindings and a filter to do what you want

IIS 7.5 delete binding


Apple ball speakers connect to MacBookPro?

Question: Is there a way to connect my apple ball speakers to my MacBookPro? The speakers have a 2.5mm jack but the MacBook Pro has a USB port.
Thanks!
Answer: You need a USB DAC (Digital Audio Converter).
I personally use a Behringer UCA202 to connect my iMac to my Bose Wave Radio (line input).

What's really nice about it is that it's powered off the USB port meaning it doesn't need an external power adapter.  It also has both left and right inputs and outputs as well as a 3.5mm headphone connection.    For best quality, you will want to use the RCA output.  You will just need an RCA to 3.5mm adapter (second picture) to connect to your speakers.
Answer: If your speakers have 2.5mm you'll need to buy 2.5mm -> 3.5mm adapter (like this) to connect it with MacBook Pro
Answer: Do you mean the Apple "Pro Speakers" by Harmon Kardon? They have what looks like a standard 3.5mm (1/8inch) audio jack, but, unsurprisingly, the collar around the end makes it very difficult to plug into anything except the G4 'anglepoise' iMac they were designed for.
Also, if memory serves, they expect a higher output signal than is standard, so their audio 'profile' may not be optimal on other Macs.


Why Adaboost with Decision Trees?

Question: I've been reading a bit on boosting algorithms for classification tasks and Adaboost in particular. I understand that the purpose of Adaboost is to take several "weak learners" and, through a set of iterations on training data, push classifiers to learn to predict classes that the model(s) repeatedly make mistakes on. However, I was wondering why so many of the readings I've done have used decision trees as the weak classifier. Is there a particular reason for this? Are there certain classifiers that make particularly good or bad candidates for Adaboost?
Comment: The simplest learner that you can possible use is the decision tree with depth=1. Maybe that's why everyone uses it in their examples.
Answer: I talked about this in an answer to a related SO question. Decision trees are just generally a very good fit for boosting, much more so than other algorithms. The bullet point/ summary version is this:

Decision trees are non-linear. Boosting with linear models simply doesn't work well.
The weak learner needs to be consistently better than random guessing. You don't normal need to do any parameter tuning to a decision tree to get that behavior. Training an SVM really does need a parameter search. Since the data is re-weighted on each iteration, you likely need to do another parameter search on each iteration. So you are increasing the amount of work you have to do by a large margin.
Decision trees are reasonably fast to train. Since we are going to be building 100s or 1000s of them, thats a good property. They are also fast to classify, which is again important when you need 100s or 1000s to run before you can output your decision.
By changing the depth you have a simple and easy control over the bias/variance trade off, knowing that boosting can reduce bias but also significantly reduces variance. Boosting is known to overfit, so the easy nob to tune is helpful in that regard.
Answer: I do not have a text-book answer. However here are some thoughts.
Boosting can be seen in direct comparison with bagging. These are two different approaches of the bias variance tradeoff dilemma. While bagging have as weak learners, some learners with low bias and high variance, by averaging the bagging ensemble decrease the variance for a little bias. Boosting on the other hand works well with different weak learners. The boosting weak learners have high bias and low variance. By building up one learner on the top of another, the boosting ensemble tries to decrease the bias, for a little variance.
As a consequence, if you consider for example to use bagging and boosting with trees as weak learners, the best way to use is small/short trees with boosting and very detailed trees with bagging. This is why very often a boosting procedure uses a decision stump as weak learner, which is the shortest possible tree (a single if condition on a single dimension). This decision stump is very stable, so it has very low variance.
I do not see any reason to use trees with boosting procedures. However, short trees are simple, easy to implement and easy to understand. However, I think that in order to be succesfull with a boosting procedure, your weak learner has to have low variance, has to be rigid, with very few degrees of freedom. For example I see no point to have as a weak learner a neural network.
Additionally, you have to note that for some kind of boosting procedures, gradient boosting for example, Breiman found that if the weak learner is a tree, some optimization in the way how boosting works can be done. Thus we have gradient boosting trees. There is a nice exposure of boosting in the ESTL book.

Why Adaboost with Decision Trees?


Basic nodal analysis question

Question: I have a question about node analysis method. The part I could not solve is the Node c's equation. In equations, C is represented by 3.Here is my question what is G5(i=GV) in the circuit. The empty wire has current but there is no voltage when I simulated circuit in Proteus. And the part makes me confused is if we have got current should we write that current in the 3rd equation. And if we write that current what is the 1/R for the empty wire. I just try to solve those equations in Matlab but the results were not the same as Proteus. Please help me, I stuck on this part in question. To conclusion, my question is should I add current in the empty wire in equations and if I add what is the G5.
Comment: I've added the corrections you need, I think. See if it that works for you.
Answer: I think you're having trouble with how ideal wires work. Ideal wires have a resistance of 0 and all nodes connected purely by wires have the same voltage. In your example, node c is connected to node d, which is ground, so they have the same voltage of 0V.
(I don't understand which node is labelled which in your equations so I'm going to use the letter names)
Your equations become:
(Va-Vb)/R1 + (Vb-Vc)/R3 + (Vb-Vc)/R4 = 0
Va = V1 = 5V
Vc = Vd = 0V
Also since node c and d are the same, R2 and R3 are in parallel which means you can combine into equivalent resistor which may make more complicated problems easier in the future
Comment: I think the OP is taking the position of trying to analyze this as if they were a Spice program. Spice programs are not able to make some of the global observations that you are capable of.
Comment: Spice programs assume things connected by wires are the same node. This can be seen in spice programs because when you click on them they will have the same node name.
Comment: I mean something different. But perhaps it's because I've dug into the methods used by the code inside. It's fine. I am not complaining. I was only pointing out something I think I see. (I can be wrong, of course.)
Answer: Node voltage analysis cannot handle your case. You have a zero ohm wire between c and your reference point d. That means the branch between points c and d has infinite conductance. That's not writable as numbers.
You of course can do a numerical limit searching process where you gradually increase the conductance between c and d. You should find that the results converge until the number range limit is exceeded in the computer.
You will get the same result faster if you discard node c - electrically it's the same as d and have only equations for nodes a and b (actually only for b, voltage at node a is fixed by the voltage source), as already suggested by others.
Answer: I think you made a very simple mistake. The set up would be:
$$\begin{align*}
V_a\:G_1+V_a\:G_4&=V_b\:R_1+V_c\:G_4+I_{V_1}\\\\
V_b\:G_1+V_b\:G_2+V_b\:G_3&=V_a\:G_1+V_c\:G_2+V_c\:G_3\\\\
V_c\:G_2+V_c\:G_3+V_c\:G_4+I_{V_1}&=V_b\:G_2+V_b\:G_3+V_a\:G_4\\\\
V_a&=V_1\\\\
V_c&= 0\:\text{V}
\end{align*}$$
This will easily solve out. Let's use Sympy:
var('g1 g2 g3 g4 va vb vc iv1')
eq1=Eq(va*g1+va*g4,vc*g4+vb*g1+iv1)
eq2=Eq(vb*g1+vb*g2+vb*g3,va*g1+vc*g3+vc*g2)
eq3=Eq(vc*g2+vc*g3+vc*g4+iv1,vb*g2+vb*g3+va*g4)
eq4=Eq(va,v1)
eq5=Eq(vc,0)
ans=solve([eq1,eq2,eq3,eq4,eq5],[va,vb,vc,iv1])
ans
{iv1: v1*(g1*g2 + g1*g3 + g1*g4 + g2*g4 + g3*g4)/(g1 + g2 + g3),
 va: v1,
 vb: g1*v1/(g1 + g2 + g3),
 vc: 0}

I think you only missed adding a term in one equation (the current in one of the equations), plus one extra equation that is required (you may have noticed that all Spice programs will require the specification of a ground reference.)
As you can see, this is pure nodal without any super node ideas or any other odd concepts required.
Using Sympy to calculate the answers is easy:
ans[va].subs({g1:1/1e3,g2:1/100e3,g3:1/4.7e3,g4:1/22e3,v1:5})
5
ans[vb].subs({g1:1/1e3,g2:1/100e3,g3:1/4.7e3,g4:1/22e3,v1:5})
4.08908995997912
ans[vc].subs({g1:1/1e3,g2:1/100e3,g3:1/4.7e3,g4:1/22e3,v1:5})
0
ans[iv1].subs({g1:1/1e3,g2:1/100e3,g3:1/4.7e3,g4:1/22e3,v1:5})
0.00113818276729361

Answer: I think Jonk has given the correct answer, but I want to explain it with words rather than equations.
Don't think of the connection between nodes D and C as a zero-ohm resistor. Think of it as a 0 V voltage source. Now you treat the zero volt source the same as you treated the 5 V source between nodes A and D.
In Jonk's answer, the equation \$V_c = 0\ {\rm V}\$ is the equation that defines the supernode required by introducing this voltage source into the circuit.
Using a 0 V source isn't uncommon and in fact in early SPICE programs, placing a 0 V voltage source was the usual way to get the program to include the current through a circuit branch in the output.

Basic nodal analysis question


When do I stop pedaling?

Question: I am playing a piano piece that tells me to use the pedal (it says (with pedal), but it does not tell me when I need to stop, nor when to release and reapply. The piece has double bar lines four measures later, but I feel like it is too soon to stop there. The only other logical place is 50+ measures later, but areas in between there do not seem to require it. Should I stop at the double bar lines or at the next section?
Comment: Can you provide us with a picture? It would make it easier to answer
Comment: @ Michael Curtis: that is "Ped." (or simply "P."), meaning pedal.
Comment: Are the 'Led' and * symbols not used in the score?
Answer: An indication of with pedal or con pedale or pedal ad lib. is a way of expressing that pedaling for a given passage is up to the discretion of the performer. If there are other pedaling indications, then those indications supersede the original indication at the appropriate time in the music. If not, then the pedaling is understood to be at the player's discretion throughout the piece.
In terms of figuring out exactly how to pedal is exactly your problem. As a performer, you need to make choices. You can make choices that fall in line with convention, recordings you have heard, or advice you get from other performers. However, when composers notate with pedal, it is understood that they're accepting of a bit of flexibility (or are simply to lazy to write out specific pedaling).
Hope that helps.
Answer: A basic rule of thumb, or should I say foot, is to lift and restep at all changes of harmony. Now, this sounds technical but it's not that complicated: It's a matter of watching the lowest bass note in the music. (It actually should be done by ear.) Take a look at a copy of Beethoven's Fur Elise. The first, lowest-sounding bass note is an 'A' you'd want to step the pedal down and hold it until the low 'E' arrives in the second measure. At the split second that you strike the 'E' lift the pedal WHILE YOUR FINGER IS HOLDING THE 'E" down and then step back down again. The changing of the bass notes from 'A' to 'E' are changes in harmony, so the trick is to get rid of the old harmony sound by lifting the pedal and stepping back down for the new harmonic structure. I call it 'taking out the trash' - if the piano sounds blurry, murky and underwater, it's time to lift and QUICKLY restep the damper pedal.  Now, when you get to the bridge, there are more harmonic changes happening more quickly than previously; so you would lift and restep for the 'C' bass then the 'G' then the 'A' and the 'E'. During the following octave 'E's', the pedal should be held down for all of the 'E's' because they're all part of the same harmonic structure. The repeating, chromatic D# E D# E D# E could go either way, depending on your type of piano (electric or acoustic), the reverberation rate of the room you're in and it could simply be a matter of personal taste. The same goes for the opening theme, there are chromatic D#'s to E's that I would pedal if playing an electronic piano but would not if on an acoustic piano.
Answer: The pedal will sustain any notes played after it's pressed. If those notes combine to make a chord, which maybe can't be held with fingers, then that's the main reason for using the pedal. When the harmony changes, it will sound pretty awful if the last chord sound continues, and bleeds into the next. Thus, a change of pedal will be needed at that point. Ears will tell, if knowledge of chordal theory won't.
Answer: 'With pedal' instructs you to use the pedal with discretion to achieve a legato effect.  It doesn't instruct you to push it down and leave it down!  It doesn't instruct you to over-use it, blurring the harmony.  You will make much use of the technique known as 'changing the pedal' - lifting it as you play a new note or chord then 'catching' them by immediately depressing it again.
General rule - even if the instruction is 'with pedal', you're probably using it too much!
Answer: Schumann gives such instruction a lot. The genre and period of the piece you are playing matter. Normally, you change pedal by the same judgment as you do normally. If there were no "with pedal" instruction, how will you plan the use of pedal? With "with pedal" instruction, it stresses the role of pedal, but it does not mean you have to use pedal everywhere. Usually, when the chord changes, you raise the pedal upon playing the first note, and quickly hit pedal afterwards. When dry effect or clear articulation is intended, you do not use pedal there. If you have further questions, consult anyone with reasonable piano playing experience. Hope this helps.
Answer: Quite simple, in this situation, I think you should go with the flow... Although I would keep the pedal on and release it at my discretion. Just remind yourself what the pedal does: it creates a legato effect for the notes played for the period it is held, creating near-silence upon release.
I said "feel there needs to be a breath" on my last edit. I in fact meant "whenever you feel it is suitable". Sorry for any misunderstanding...
Comment: Why did I gain 8 reputation on this answer?
Comment: Don't think you did! I downvoted, as keeping the pedal down for effectively a whole phrase is not good playing. In that phrase there may be a couple if not several harmony changes, which, if the pedal is kept down, will blur into each other and sound muddled. See Laurence's answer.
Comment: @Tim, what do you think I mean? What do you think I mean by a "breath"? I admit that that is not the best way to put it, but you have clearly misunderstood me...
Comment: By breath, I think you mean a phrase, or line that stands by itself.
Comment: @Tim of course not! I'll edit it within 15 minutes if I have time

When do I stop pedaling?


As an adult, how should I choose a flute?

Question: I learnt to the play the flute as a teenager. I want to play for children. My hands weren't great in dexterity as a teenager and probably a bit worse. I haven't played for 10 years. I live in Japan and while there are music shops, they aren't great.  What should I consider when choosing a flute whether in person or online?
Comment: Well, it kind of depends on how long you expect the instrument to last and whether the children you are going to play for will lay their hands on it. It also depends on whether you have played another instrument before or not. If you are a past saxophone player, I would recommend a closed-hole one. From personal experience, the price doesn't really affect much when it comes to flutes. In other words, there's no need to pay $10k just because it's a silver model. Try finding a dedicated flutists' forum online and ask for an opinion there.
Comment: I'm a clarinet/sax player that recently added flute to my arsenal.  My strategy was to buy one from my regular instrument repairman.  That way I could explain what I was looking for and I knew that what I bought would work and not be too expensive.
Answer: My first piece of advice is play as many as you can get your hands on. This may involve some travel.
Next, think about how much you're thinking you're going to spend on this instrument, then about double it or so. Unless you're already familiar with what instruments cost, there's often a fair amount of sticker shock involved with buying a horn.
The next thing to consider would be brand. I don't know if Japan has an equivalent, but in the US there's the National Association of Band Instrument Repair Technicians (NAPBIRT). If you can find someone that is associated with them, you can get their opinion on good instrument brands. One word of caution: a lot of people will tell you that anything that comes out of China is garbage. They have good reason to do so: that used to be true. See the end of my post. The reason I tell you to seek out a repair technician is that, while a particular instrument may sound good or be less expensive, if it's a bad instrument then there's a good chance that you won't find a respectable repair shop to fix it. I worked at a band instrument repair and sales shop for eight years, and when those sorts of instruments came in, the techs would put their hands behind their back, take one step away and say, "No," because the repair guarantee on them was "30 feet or 30 seconds", meaning they couldn't guarantee their work on them.
The next piece is to decide what level of instrument you want. You may currently only want to play for children, but that may change in the future, so perhaps an intermediate flute might be a better choice. Seek out an open-holed flute; don't worry about having to play it exactly right right away, they come with plugs to turn them into closed-hole flutes.
Beyond that, it's more or less up to you. You and I could play the exact same instrument set-up and get completely different sounds; that's because the biggest influencer on how you sound is you.
Okay, now that I've gotten all that out of the way:
Go buy a Di Zhao DZ-300. Yes, they come from China. Yes, I'm suggesting that you buy something without trying it first.
The owner of the band instrument store where I worked used to be the president of NAPBIRT, so you can trust his opinion on instrument construction. When we started stocking these things, they started flying off the shelves. I worked there another 3 or 4 years after we first got them in, and we still sometimes had trouble keeping them on the shelves.
The DZ-300 is open-hole and it's got the B-foot, which is a somewhat advanced feature, but it's lower-intermediate instrument. Brand new it'll be around $600-$800 USD, but it'll sound like a flute that costs twice as much. I'm confident you won't be disappointed.
FINALLY, once you get a horn, go take at least a couple lessons with a private teacher. A few lessons at the beginning can help correct or prevent mistakes in technique that take years to break, if they even can at all.
Answer: Don't buy so cheap that the thing will impede your progress or fall apart after a few months. Notwithstanding the advice above to seriously look at Di Zhao (I've read many positive reviews), Japan has a thriving flute industry. Personally I've had good luck with Yamaha and Pearl. Jupiter too (I think they are from Japan).
One feature to look for is offset G key because of a straighter left wrist angle puts less of a strain.
Comment: Thriving industries in Japan are often not that present in  Japan itself such as good road bicycles.
Comment: Jupiter is from Taiwan. I don't know about their flutes, but their saxophones seriously suck.


How do I identify the lens mount used for an old Soligor lens?

Question: Soligor wide-auto 1:2.8 f=28mm
Comment: Adapter to go onto what camera?
Comment: I've edited the question; I think it's actually one step earlier than asking for an adapter, but simply asking what mount it's made for. From that, you can figure out the right adapter for any other specific mount (if that combination is possible).
Answer: This lens was made in many, many different versions over the years — Soligor primarily (or exclusively?) licensed other company's products and attached their name. This forum post identifies at least 21 different versions, and those may come in multiple mounts.
I'm pretty sure that this one has an old Minolta bayonet mount (Minolta MC/MD). That's substantiated by the label MIN, which presumably indicates Minolta. You can compare many old lens mounts on this page — or, a google images search can be very helpful too.
For adapting this to a modern DSLR, the bad news is that the flange focal distance is roughly the same as modern lens mounts. See Is it possible to adapt lens from one brand into another brand's body? for more on that. You can get adapters, but they need to contain glass in order to retain infinity focus, and therefore will either be very expensive or compromise image quality. If, instead, you want to adapt to a mirrorless camera system, you may have better luck — see for example How can I use a manual-focus Minolta MC Rokkor-PF 55mm SLR lens on a four-thirds system?
Comment: @Blrfl the link to KEH's blog is dead (they killed kehblog.com, migrated it to blog.keh.com). Here is the [updated link to the lens identification guide](http://blog.keh.com/2011/12/02/the-lens-mount-guide-part-1/).
Comment: KEH has a [pretty extensive identification guide](http://www.kehblog.com/2011/12/lens-mount-guide-part-1.html), too.
Comment: Agree, the notch configuration and aperture ring coupler look like MC/MD
Comment: The KEH link is *again* updated and is now three parts. part1: https://www.keh.com/blog/the-lens-mount-guide-part-1 part2: https://www.keh.com/blog/the-lens-mount-guide-part-2 part3: https://www.keh.com/blog/the-lens-mount-guide-part-3 Note it's less that usefull now that somehow the img tags were stripped (you need to click each one to see the image!)


What is the evolutionary advantage of albinism in cave-dwelling animals?

Question: In a story I'm writing, there is a species of extremely rare cave dwelling bird. A scientist and a plummer have to find a specimen of this bird before it goes extinct. When they finally find it, the plummer asks why it is white, and the scientist explains why (most) creatures in caves are albino, but the problem is, I don't know why animals in caves are albino. Can you guys help me?
Comment: Hello Ttagmonster1345, and welcome to Worldbuilding! Making pigments requires materials and energy. Why make pigments when nobody can see the colors? Animals which don't waste materials and energy making useless pigments can use them for something useful, thus obtaining a competitive advantage. Please consider taking the [tour] in order to become acquainted with the purpose of this site...
Comment: To follow up on what @AlexP said: there's not much food in a cave.  Not need to spend energy on pigment means that you can survive longer when food is scarce.
Comment: @manassehkatz I assume the OP meant "plumer" - i.e., someone who seeks out birds for their plumage. But I agree, OP should clarify this point.
Comment: It isn't that they need to be albino,  it is that there is no benefit to being colored.  @Alexp and  and RonJohn, IMO, yout comments answer the question.   Should they be answers?
Comment: What is a "plummer"? Is it a plumber? If so, why is a plumber working with the scientist in caves? And if it is something else, please explain. I have found various possible definitions, none of which make any sense.
Answer: Cave creatures aren't white as much as they are "I don't care what color I am."  It just happens that when you look at all the different compounds required to keep a creature alive, they tend to roughly reflect all of the spectrum equally.
Consider this as an example: the Olm

In this picture we can see that the whole creature is white.  However, its gills are an exception.  They are red because the hemoglobin in its blood drastically adjusts the absorptivity of the blood to be more red.  In fact, if you look at the whole body, it's not actually "white" as in Titanium White.  It actually has a reddish hue throughout due to the hemoglobin in its body.  However, this is such a slight effect compared to what you or I are used to seeing that our brains register it as "white" or even "unusually white."
To have a color, creatures would need a predominance of one chemical or another, like we see with the hemoglobin in the blood.  The dark pigments in our own skin are an example of this.  Melanin makes our skin dark, and the quantity of melanin we have is enough to have it play a substantial effect in the color of our skin.  This melanin is not cheap.  Current science believes it has a half life on the order of weeks, meaning we have to be constantly replacing it.  Melanin requires the oxidization of tyrosine, an amino acid.  A species which forgoes its production can use that tyrosine for other purposes (it's a major player in signal transduction).  Over an evolutionary period of time, this can make enough of a difference in survival to cause a species to discard its ability to produce such pigments all together.
Answer: Best use of available light
Caves are naturally dark. But sometimes there is a little light - either reflected from the entrance to the back of the cave, phosphorescent minerals, or perhaps artificial light in some form. But the light is limited, so the best visibility is provided by the highest contrast between animals and the background - and that means white animals.


Is it possible to buy a 24-hour ticket at Copenhagen airport in advance?

Question: Is it possible to buy a 24-hours ticket (not a city pass) at Copenhagen airport in advance and validate it in a bus the day you want to use it?
Answer: No. Unless I misremember, the 24-hour tickets used to be cardboard tickets with the same format as the 10-punch strip tickets, which you would validate when first boarding a bus or train. But these strip tickets were discontinued several years ago in favor of contactless stored-value cards, so the mechanical validators have been removed from buses.
Your options are:

Paper 24-hour tickets can be bought from vending machines at any train/metro station, so if you're staying somewhere reasonably central you may not need to buy it in advance.
On Android or Iphone, download the app DOT Mobilbilletter linked from http://dinoffentligetransport.dk/service/for-tourists/tickets/. The app lets you pay with a payment card and does speak English. You show the ticket on the phone screen to bus drivers and ticket inspectors.
Finally it can be bought as an SMS ticket, paid for by replying to an overtaxed SMS message. The transit agency promises this works with foreign phone numbers, but the instructions at http://dinoffentligetransport.dk/hjaelp-til-billetter/salgssteder/apps-og-sms/sms-billet/ and http://dinoffentligetransport.dk/billetter-og-priser/find-og-koeb-billet/koeb-billet/ only seem to be available in Danish, so you may need to get someone such as a hotel receptionist to help you with the procedure.


Why won't my ps4 controller connect to my ps4?

Question: I bluetooth paired my ps4 controller to my ps4 just fine. Then i deleted the bluetooth controller account (ps4 controller)off of my ps3. Now no matter what I do my controller won't work for the ps4. I click the home button and it blinks once then turns off. Someone please help me before I loose it.
Answer: I think that pushing the reset button on the controller might help you.
From this answer:

If your controller won't pair, won't respond, or is displaying a flashing
  light, please follow the instructions on how to reset the controller:

Turn off the PlayStation 4.
Locate the small reset button on the back
  of the DualShock 4 near the L2 shoulder button.
Use a small, unfolded
  paper-clip or something similar to push the button (the button is
  inside a tiny hole).
Hold the button down for a couple of seconds and
  release.
After resetting the controller, re-pair the controller with
  the PS4 by connecting the USB cable to the controller and the system,
  and turn the PS4 on.
Press the PS button to log in to the PS4
Comment: There is a strong possibility that step 5 is the only one needed here.  The easiest way to pair your DS4 with a PS4 is just to connect it with the cable.
Comment: @Gendreavus: I agree. The reset button is only needed when you can't connect via a cable. After pressing the reset, the DS4 will send out a "broadcast" when activated (which inherently means the DS4 isn't paired to anything) which prompts the PS4 to pair with it (the first PS4 to respond to the request, in the rare case where there are multiple). If you have a cable, all that happens automatically and you can guarantee which PS4 you will pair with (in case of multiple).
Answer: It is fundamentally important that you press the PS button on the controller in question while the PS4 is powering up, and the blue light is blinking - do not wait until the system prompts you to press the PS button, it's too late.

Turn off console.
Connect controller with micro-USB cable.
Turn on console manually (button on front left of PS4), and when the button lights up blue press the PS button on the controller.

In my recent experience the system took a couple of extra seconds to recognize the controller, but then it worked. I too tried all of the above troubleshooting techniques and none of them worked until I got the all-important timing correct. You'd think Sony would take care to mention this little detail.


Is there a way to affect a familiar with a spell that targets animals?

Question: Basically what i had in mind was a way to target a familiar with Anthropomorphic animal so that he can manipulate tools and speak, but since a familiar becomes a magical beast, it shouldn't be posible.
Is there a way around this?
Comment: The only way I know is first turning your familiar into an animal with Polymorph and then use Anthropomorphic animal on it. But that seems kinda silly and pointless.
Comment: @LouisHuppenbauer While the relevant rules, admittedly, could do to be a lot clearer and more explicit, Polymorph by itself does not change the subject's creature type. I think there might be some ways to get around this, though; certainly, the psionic equivalent (the Metamorphosis line) does have some ways, via class abilities and the like, to get them to change creature type.
Answer: All you need to do is cast the spell on your own familiar. Familiars, from master level 1, have an ability that has you covered:

Share Spells: The wizard may cast a spell with a target of "You" on his familiar (as a touch spell) instead of on himself. A wizard may cast spells on his familiar even if the spells do not normally affect creatures of the familiar's type (magical beast).

Emphasis mine. This clause is usually used to allow buffs to work on familiars that usually only work on humanoids, but it works just as well with buffs that usually only work on animals. Note that you can save a spell level and accomplish similar results with the Alter Self spell, though that one won't allow it to speak a language unless it has one to use, so if planning to do that version with any regularity, you'll want a thrush or raven as the base familiar.
Comment: @DuckTapeAl The language is VERY clear. What it was intended for is not, but the wording absolutely does not even slightly support your position. They had *every possible chance* to say "even if the spells normally only affect animals", but instead they made *no mention at all* of the animal type, and said "even if the spells do not normally affect creatures of the familiar's type". This is not merely fairly clear, it is a fantastic degree of clarity of wording which is rarely to be found in RPG books.
Comment: @claudekennilol **Read the ability I quoted.** It has two **separate** clauses. One allows spells with target "you" on the familiar, the other allows spells that don't target magical beasts. Neither one requires the other to also be applicable. If it did, the ability would be pretty much useless, since there are almost no spells with both a target of "you" *and* a creature type requirement.
Comment: -1: That line doesn't use super clear language, but I'm fairly certain that it's only there to let you use self-targeted spells that don't work on animals on your familiar.  It seems sort of weird to be able to ignore all creature type requirements for all spells on your familiar, whether you're using your Share Spells ability or not.
Comment: Since when is Anthropomorphic Animal (a target of animal touched) a spell with a target of "you"?  You, the PC, cannot target yourself with this spell because you're not an animal.  Pathfinder definition of animal _An animal is a living, **nonhuman creature**, usually a vertebrate with no magical abilities and no innate capacity for language or culture._

This is so you can cast spells such as Enlarge Person on your familiar.  You are a legal target for such a spell you cast yourself--therefor you can cast it on your familiar.  You are not a legal target for anything that targets "animal".
Comment: Also, your own example (Enlarge Person) would, under your version, have the same problem as Anthropomorphic Creature, since it doesn't have a target of "you" either. The Share Spells ability says nothing about "being *able* to target yourself", it says it has "a target of "you"". The latter is a very specific reference to the way personal spells are defined by the game (range of "personal" and target of "you" are 1:1 correlated in the spell descriptions).
Comment: You're right in this, I was merely being too argumentative because you were wrong with the other statement about familiars being able to use tools and didn't think through what you posted well enough.


Is there a point and shoot that offers "on-camera" creative photography features as in cellphone apps?

Question: Generally I enjoy using cellphone apps such as kitcam or hipstematic.
But I want a better camera.
I would like to be able to control DoF, aperture and iso, but I would like to see the result with the filters while shooting.
Is there a good p&s that offers a nice set of features as in cellphone apps?
Thanks.
Comment: Latest Samsung cameras as well as Nikon Coolpix 800 use Android as their operating system, which I can imagine, will allow to program custom post-processing filters just like apps.
Comment: Honestly, it is never something I've looked at since these things are irreversible and can always be replicated with flexibility on a computer with the right software. I do know that Casio is big on those types of features but you'll have to do some digging.
Comment: @PavloDyban - The disconnect is that for example, you may have Instagram installed on the Nikon Coolpix S800c(Android), but it is a _separate_ app then the Nikon "Shooing" app. You can't control aperture _inside_ of Instagram since Instagram doesn't support that. So essentially what the user is asking for is a camera that works just like Instragram in that it has previews of filters during the shoot, but also has full manual controls. I don't know of anything that exists such as this quite yet.
Comment: @dpollitt My first compact camera Sony DSC W300 has had b/w & sepia modi which were applied instantly & irreversibly.
Answer: Most of the current generation of pocket-size point-and-shoots have some features of that nature, although the names for each mode might change by manufacturer. (In fact, some DSLRs do as well -- Canon started including them on the T3i.) One thing I've noted is that in some cases, the camera doesn't degrade the image enough to be convincing; the toy camera mode on my Canon A2200, for example, doesn't change the optics of the image like a plastic lens would, and the bluescale mode looks great but isn't a particularly convincing mock-cyanotype.
My personal take on the matter: fix it in post. The features are going to be there on most brands, but you don't gain much from it.
Also, you asked about changing DoF and the like. I'm not sure about most brands, but for Canon cameras, CHDK does let you tweak the aperture, so that's something to experiment with.
Answer: My sony rx-100 has some picture effects (toy, black and white, selective color, miniature, HDR, soft focus,...) and some of them are visible while shooting.
Here's a YouTube link showing the modes http://www.youtube.com/watch?v=jDly1wOB0X8


Changing front forks

Question: I have a giant rincon from the 90's and I want to put suspension forks on them and keep the 26" tire what size forks should I be looking into getting
Comment: Welcome to the website! A picture of the front of your bike should help identifying what parameters your current fork has, and what replacements (if any) are out there compatible with your frame.
Answer: If the bicycle has a rigid fork now and this fork is not marked as having "suspension-corrected" dimensions, in particular, axle-to-crown length, then this bicycle is not officially compatible with any suspension forks. Simply put, installing such a fork will either raise or lower the front of the bike, which will affect its steering properties and ground clearance among other things. There may be other problems, like the new fork's crown touching the downtube when turned.
If the current fork is "suspension-corrected", then it should be possible to replace it with a suspension one. Bikes of the era rarely had suspension travel more than 100 mm. There are other compatibility parameters to consider though, like steering tube diameter and shape, wheel axle type, brake system etc.
A bigger issue is, however, that 26"-wheels and accompanying components are (unjustly IMHO) considered obsolete by the market. It is hard to get new good parts for them, as most of new MTBs are sold with either 27.5" or 29" wheels. Those few cheapest new bikes with 26"-wheels out there are coming with OEM forks (i.e. those cannot be bought separately), and those forks are not especially known for their stellar damping properties.
The dirt jump bikes are however fixed to the 26" wheel size. It should be possible to get an aftermarket fork with 80-100mm travel for them. However, as I mentioned before, they tend to have modern "standards" elsewhere, such as through axles, tapered steering tubes and disc brakes, things not known in 1990's.
Comment: I just checked the first eshop and there are many 26" forks available. Some with V-brakes or dual. They do come from OEM manufacturers and are just branded by some cheap brand (SR Suntour and Force in this eshop) but that may be more than adequate for that kind of bike.
Comment: @VladimirF yeah. However, it is often easier to get decent damping from a *rigid* steel fork than from a "suspended" cheap SR Suntour. I am even not talking about trail-worthy huck-eating suspension, just something capable of smoothing out gravel road chatter. Cheap "suspension" forks are both heavier than their rigid counterparts, they do not do their job well, and they are less reliable than a plain rigid fork, while costing as much.
Comment: I don't do MTBs but I will side with Grigoriy on this. A rigid steel fork plus a decent tire provides enough suspension for the average rider who isn't using the bike in a performance setting.
Answer: You need to match the axle-crown height (on the loaded suspension), the Steerer (if early 1990's will likely be impossible to find quill stem, otherwise straight 1 1/8") Modern forks used tapered steerers so be carefull. You will also need to match the axle, which will be 9mm QR not through axle, and the fork wil have to have V Brake bosses unless you want to upgrade to disc brakes (means new hub which practically means a new wheel)
You can get new forks that will fit the requirements, but they are from lowest end range of what is manufactured today by low end manufacturers - cheap and generally pretty nasty.  Quality forks from a donor bike upto early 2000's might be a better way to go (after that quality forks wen disc), but age will have taken its toll unless well maintained and not used much.  Examples of used forks that fit the bill are getting expensive.
Ultimately, it fits into the fun(*) to do but not economical bracket unless you can find good used parts, which is the real challenge.

Fun - something you do that is challenging, time consuming and costly just because you can.

Changing front forks


Use everyauth package for authorizing users to access data via REST api calls

Question: I am developing a google chrome extension that needs to communicate with a nodejs server. I was wondering if its possible to use everyauth package to simplify authentication. For starters, I just wanted to use simple password based authentication. But from the examples and the documentation ,as well according to my trial, it seems to me that everyauth is designed to be used for a webapp and gives me errors if i don't set the getLoginPath. Also i am not sure how to configure everyauth to send the user details or errors after user authenticate in a json payroll rather than redirecting user to a particular page. This is my first project with node.js and I am looking for some advice on how to go forward with this. I am open to using some other package/library that provides such authentication,
Answer: Since you are open to using other modules, as the developer of Passport, I'd suggest you look at it: https://github.com/jaredhanson/passport
Passport is designed to be a simple and unobtrusive authentication library, which makes it easy to get up and running quickly.  It's also modular and extensible, which allows it to adapt to your applications needs over time.
The examples provided, along with the local strategy ( https://github.com/jaredhanson/passport-local ) are enough to get you started with username/password authentication.  Let me know if you have any feedback or questions.
Comment: Do you have any idea how to use passport RESTfull auth? (see http://stackoverflow.com/questions/14572600/passport-js-restful-auth)
Answer: I was able to accomplish a REST-only interface to everyauth by overriding its handler methods: https://gist.github.com/2938492


With feminine nouns, how do we know that две and три take the genitive singular rather than the nominative plural?

Question: With masculine and neuter nouns, два and три take the genitive singular. With feminine nouns it is at least usually taught that две and три also take the genitive singular. But how do we know? Given that this form of a feminine noun is almost always the same as the nominative plural, can we not with equal justification say that these numerals take the nominative plural? Or might we not say that they take the form that expresses both of those functions?
Comment: So, you don't like the simple rule and you want to have a complex rule with the same outcome? Don't forget about words like "сестра" which have different stress in genitive and nominative plural.
Comment: Also "гроздья" - nom. pl. but "грозди" - gen. sing.
Comment: Related https://russian.stackexchange.com/questions/13618/%d0%af-%d0%b2%d0%b8%d0%b6%d1%83-numeral-noun-governed-by-what-case
Comment: "_Given that this form of a feminine noun is always the same as the nominative plural_" - well, this is not given! It's not correct.
Comment: I'd forgotten about сестра. What other such words are there? Are they all in a small group where the only change is in stress? I've noticed that many Russian people will say that две takes the nominative plural. So we could perhaps define an unusual nominative plural for words in this small group. There is a question of form and function.
Comment: Also сова, гроза, нога, рука, сопля and others.
Answer:
But how do we know?

Historically, Russian cases are defined by the questions the nominals put into each case answer.
This might not the best way to define a case, because using this definition you can't tell partitive from genitive as in чая vs чаю, or locative from prepositional as in о лесе vs в лесу, but it's how it works in traditional grammars which trace back to Meletius' Church Slavonic grammar.
However, this definition is good enough to tell the two cases apart in your case. You can't ask in Russian две кто? or две что?, you'd have to ask две кого? or две чего? which undoubtedly puts the corresponding word into genitive or its varieties (or which nominative is not).

Given that this form of a feminine noun is always the same as the nominative plural, can we not with equal justification say that these numerals take the nominative plural?

The feminine nominals are not always the same as nominative plural as in genitive singular.
The paradigm differs for all adjectives and ordinal numerals:

красивые (f. nom. pl.) / красивой (f. gen. sg.)
первые (f. nom. pl.) / первой (f. gen. sg.)

, for nouns with mobile stress:

ре́ки (nom. pl.) / реки́ (gen. sg.)
во́ды (nom. pl.) / воды́ (gen. sg.)

, for nouns with a mobile vowel in the root:

сёстры (nom. pl.) / сестры (gen. sg.)
зори (nom. pl.) / зари (gen. sg.)

, for ad-hoc declension paradigms resulted from the gender shift:

гроздья (nom. pl.) / грозди (gen. sg.)

This said, numerals in две, три and четыре undoubtedly govern singular genitive even for feminine nominals.
Comment: Good answer. Аnd for "three of these" one says три этой rather than три эти.
Comment: @TheEarth Well you say neither because "three of these" does not have a natural equivalent in Russian. The most natural thing to hear would be "эти три" ("Видишь сливы? Эти три съешь, а остальные унеси"). But usually there's some kind of noun there ("три килограмма вот этого", "эти три штуки").
Comment: I've heard native speakers say "три этой" to mean "three of these (postcards)(открытки)", the noun being understood. Your examples don't translate to English phrases containing "three of these".
Comment: @The Earth i can envision a native speaker say "десять этой" and in fact any numeral, but such use pertains to a specific situation where there's say a product whose gender is feminine and the person asks a vendor to allocate them so and so items of this product, it's in fact a shorthand of a phrase "три **штуки** этой", and as we can see the word whose Genitive is governed by the numeral is штуки, whereas Genitive of этой is in turn governed by the noun штуки (кого? чего? - этой)
Comment: That's "десять (штук) этой (открытки)". What I've heard is "десять этих (открыток)" and "три этой (открытки)".
Answer: I'd argue that the case of сестра is a proof that the Genitive feminine form is singular and not plural. Other such words are башка (if we accept its Nom. pl. as бошки, Gen. - башки) and весна (вёсны vs весны respectively), зима (stress variation: зИмы vs зимЫ respectively), беда (stress variation: бЕды vs бедЫ respectively).
We also may consider two other genders which clearly provide singular forms and i personally as a native speaker (which isn't of course any proof) perceive the feminine flexion as of a singular form and because with numerals you expect some sort of oblique case.
In my opinion the forms of feminine Nom. pl and Gen. sing (in this particular case) are simply homonyms, they are spelled and often sound alike but function differently.
But maybe historical philology can provide more conclusive clues.


Can't pick custom folder?

Question:
Under System Settings > Desktop, when I click "Custom" in the dropdown box, I get the above window to pick a folder. But I can't seem to choose anything! There is no "open" button. I can't even exit the selection screen. Am i missing something or is this a major bug?
Answer: I figured out that this was because I edited the GTK settings (org.gnome.settings-daemon.plugins.xsettings).
Resetting the schema solved the issue.

Can't pick custom folder?


Can an non US citizen/non resident open an US bank account for his LLC with a tourist Visa?

Question: I'm starting an ecommerce business from my origin country and I will sell products in the USA . I need to open an US bank account in my business name. I already have an LLC and I need to know is it possible to open this bank account with a B-2 Visa?
Answer: Generally, to open a business account in the USA, you need to prove that the business exists as both a physical and legal entity, that it's set up appropriately with the IRS, and that you (personally) have proof of identification.
To prove the existence of the business, you'll need to provide articles of incorporation or some other legally binding documentation that establishes the business's structure and identity. Some banks may want other documentation about the business, depending on the structure (i.e. if there are multiple owners, they will want to see something describing their roles). You'll also likely need to prove that the business has a valid physical address in the US - via utility bills with that address on them, or (ironically) bank statements or other legitimate mail to a US address. Proving the address can be a bit of a chicken-and-egg game, because you may not yet have utility bills or other official mail if you don't have a bank account. Some banks will accept your EIN paperwork as proof of address. Proof of your own identity can usually be done with your passport.
The other major requirement is proving your relationship with the IRS. Basically, the bank will want a tax identification number (TIN) of some kind. If you are set up "doing business as" yourself, and you have an SSN, you can use that. If you don't have a US SSN, you can obtain an ITIN (individual tax ID number) for yourself. Or, if not operating as a sole proprietorship, you will need to obtain an EIN (employer identification number) for the business. Obtaining an EIN is easier if you, personally, have a TIN already - if you do not have a TIN, you cannot apply for an EIN remotely, you'll have to do it in person.
Answer: dwizum's answer is great, but let me answer your specific question about the visa - which you might have asked on our Travel site.
Technically a B2 visa does not permit you any business activities, which this would count as. However in a lot of cases an application for a B2 gets a B1/B2 visa which combines the allowed activities of both. A B1 visa would certainly let you set up a bank account.
A bank probably isn't going to check that you have the right visa to open an account, but if you have a strict B2 visa it might be safer to apply for a B1.


magento 2 import logs

Question: i'm having a problem importing additional_attributes for products. i have them formatted the way the export file looks, but when i import them, it shows import completed fine but does not update any of the custom attributes. are there any logs available for magento 2 imports? i checked out this article, Are there any csv import logs kept?, but it appears to be for magento 1.
Answer: Attributes from additional column can be separated to columns on import, you can find working example file here https://github.com/firebearstudio/magento2-import-export-sample-files/blob/master/Improved%20Import%20:%20Export%20-%20Sample%20Files/products_all_types.csv
By default Magento 2 don't have import logs, only output which you get after run import on admin, our free extension add some logging to file https://github.com/firebearstudio/importexportfree

magento 2 import logs


Filling in ESTA Application - Country of Birth where I was born abroad but on sovereign territory

Question: I'm currently in the process of filling in the ESTA form for a holiday in America.  The section "Country of Birth" is required; I was born in Germany, but to British parents on a British RAF base, and I'm British and have a British birth certificate.  I have no legal connection to Germany at all.  Do I put my country of birth as Germany or UK?
Comment: What exactly is stated in your birth certificate and passport? Only the RAF station name? (In Berlin it was called **Royal Air Force Station Gatow**)
Comment: @Mark My birth cert says "British Military Hospital, Rinteln".  Doesn't mention the country at all.  My passport just says "Rinteln".
Comment: Many passports will only add extra information if the city/town name is not unique. In this cases Rinteln is a town in Germany.
Answer: You were born in Germany.
The UK does not have sovereignty over its military bases in Germany. They are still part of the host country, but under extraterritoriality, similar to embassies. For most purposes Germany does not have jurisdiction there, but still asserts sovereignty.
There are separate questions on any former or present nationalities.
Comment: Whilst this answers the case of Germany, and is generally the rule, it might be worth mentioning the special case of Cyprus, where the UK has retained sovereignty of its bases as enclaves in what is otherwise a independent sovereign nation.


Evolution in fruits

Question: So, I saw a video on YouTube that says the banana we eat today is not what a banana looked like years ago. Since the banana has been genetically modified over the years, does that qualify as evolution?
Answer: Yes. Modern domesticated bananas have evolved from ancestral wild species under the influence of humans. Quoting D'Hont et al.: (1)

The [banana] domestication process started some 7,000 years ago in
  Southeast Asia. It involved hybridizations between diverse species and
  subspecies, fostered by human migrations, and selection of diploid and
  triploid seedless, parthenocarpic hybrids thereafter widely dispersed
  by vegetative propagation.

Modern bananas have undergone extensive evolution from the original wild species. The selection pressure has in part been provided by humans, who have selected the most nutritious/tasty/desirable examplars and facilitated their reproduction. This can be considered "artificial selection" as opposed to "natural selection", but does not change the fact that an evolutionary process has taken place. The UC Berkeley website "Understanding Evolution" gives the following definition of "artificial selection".(2)

A process in which humans consciously select for or against particular
  features in organisms. For example, the human may allow only organisms
  with the desired feature to reproduce or may provide more resources to
  the organisms with the desired feature. This process causes
  evolutionary change in the organism and is analogous to natural
  selection, only with humans, not nature, doing the selecting.

Thus, whether the selection is considered "natural" or "artificial", the end result is evolution.
Comment: "Modern" should be understood as "domesticated". The wild [relatives](https://en.wikipedia.org/wiki/Musa_%28genus%29) and even [ancestors](https://en.wikipedia.org/wiki/Wild_banana) are still there:
Comment: Yes. Good point.
Comment: It's just selective breeding, not evolution. Far from it.
Comment: I actually got an answer from watching Cosmos. It's called Artificial Selection - the reason why we have different breeds of dogs today.
Answer: You could say it clasiffies as evolution only if you accept that the artificial things humans have done to bananas are actually natural occurences. I personally don't think they are, because intent is at play here, and evolution is a natural process without intent.
Evolution is not when something gets better. That's the misconception behind your question.
If humans would just happen to eat the tasty bananas first, what would happen is negative selection and all the remaining bananas (which lived long enough to reproduce) wouldn't be tasty. Bananas would get less tasty in order to survive.
What actually happened goes against the natural process of selection, and is something completely different to the concepts of evolution which led to us evolving intelligence, for example. This is just selective breeding. Nothing as grand as evolution.
Evolution is a natural process which led to intelligent species from single-cell organisms, and is a continuous process of random mutations being selected for or against by natural causes. Evolution has no intent and is a natural random process. A grand one, as all biology depends on it, and we depend on it.
Genetic engineering, on the other hand, has intent to improve things, and happens on a much smaller scale than the natural process of evolution. Genetic engineering of any kind, whether it be tinkering with the genes or just inbreeding to create a new breed, is artificial and is being done by an intelligent creature as opposed to nature. Calling genetic engineering a tool for evolution is the same mistake that eugenics proponents made.
Comment: I agree somewhat with the "humans are different" idea, but I still think declaring humans and human influence as "unnatural" is rather arbitrary. Species affect each other's evolution all the time, and I see no reason why the level of cognitive abilities of humans should change the name we use for that process. I see your point though.
Comment: I must disagree with this answer - I have updated my own in response.
Comment: I still disagree with you, as I believe evolution is a grand process that can only be tied to natural selection, not artificial selection. But then again, whenever you reach humans in evolutionary biology you're bound to be up against something that is completely different from the several billions of years prior to development of human intelligence.
Comment: Evolutionary biologists consider artificial selection to be a valid input into the process of evolution.  Evolution is the gradual change itself, over time, and the varieties it produces are selected against by various criteria.
Comment: By this argument human are almost incapable of evolution, since it is humans who decide who they mate with.

Evolution in fruits


How can I delete or shift certain sections of the Timeline?

Question: I'm using a single Blender file to create a 2D slideshow (with animated graphs and stuff). So all the "slides" are in this file. They are of course not actual slides, but sections of the Timeline (so the entire slideshow is run by pressing alt+A). How can I make space in the Timeline to "insert" a new "slide", or how can I "delete" a "slide"?
Answer: In the Dope Sheet editor, you can select a specific keyframe, or several of them (use B to border select), and move them with G. You can delete the keys with Suppr or X.
To go further, maybe you could create an Action for each slide, that's a great way to manipulate them using the NLA editor (basically, each slide will act like a movie clip in a video editor). NLA Editor Action Editor


Prevent zoom reset when using manipulate with Graphics3D

Question: I am creating a series of "apps" as study aids for the Engineering Statics course that I teach. I am usually able to solve most of my "problems", but I am stuck on a simple one. The code below allows a user to visualize a 3D force vector that has its position controlled with two angles, a1 rotates the plane that contains the line of action of the vector about the z-axis and b1 rotates the vector out of the xy-plane.
The user can use the mouse to rotate (LMB), pan (Shift+LMB) and zoom (Ctrl+LMB) the graphics. When the user adjusts the manipulate sliders the rotation and pan settings remain unchanged, but the graphic "snaps" back the the default zoom setting. I would like to prevent the zoom reset.
I am sure that I am missing something simple, but I have been unable to find a post that mentions this issue. If someone has a solution, I would greatly appreciate it if they would pass it along.
A second small issue... does anyone know how I could add the degree symbol to the label of the slider?
cd[x_] := Cos[x*\[Pi]/180.0];
sd[x_] := Sin[x*\[Pi]/180.0];
r = 10;
Manipulate[
 Graphics3D[{
   Style[InfinitePlane[{{0, 0, 0}, {1, 0, 0}, {0, 1, 0}}],
FaceForm[{LightGray, Opacity[0.2]}]],
   Style[HalfPlane[{{0, 0, -1}, {0, 0, 1}}, {cd[a1 ], sd[a1 ], 0}],
FaceForm[{LightGray, Opacity[0.2]}]],
   Style[Arrow[{{0, 0, 0},
  f*{cd[b1 ] cd[a1], cd[b1] sd[a1], sd[b1]}}], Black, Thick],
   Style[Cuboid[{0, 0, 0}, f*{cd[b1 ] cd[a1], cd[b1] sd[a1], sd[b1]}],
 Opacity[0.01], EdgeForm[Directive[Thin, Gray]]],
   },
  PlotRange -> {{-r, r}, {-r, r}, {-r, r}},
  Boxed -> False,
  Axes -> True,
  AxesOrigin -> {0, 0, 0},
  BoxRatios -> {4, 4, 3},
  AxesEdge -> {{-1, -1}, {-1, -1}, {-1, -1}},
  ViewProjection -> "Orthographic",
  SphericalRegion -> True,
  Method -> {"RotationControl" -> Dynamic@"Globe"}
  ],
 Control[{{a1, 30, "\[Theta]"}, 0, 360, Appearance -> "Labeled",
ControlType -> Slider}],
 Control[{{b1, 30, "\[Phi]"}, -90, 90, Appearance -> "Labeled",
ControlType -> Slider}],
 Control[{{f, 10, "\!\(\*SubscriptBox[\(F\), \(mag\)]\)"}, 1, 10,
Appearance -> "Labeled", ControlType -> Slider}],
 TrackedSymbols :> {a1, b1, f}]

Answer: The best solution in this case will be to not recreate whole Graphics3D when th slider is manipulated. It can be done by simply adding Dynamic to the primitives inside (lookup 'nesting dynamic' to learn more).
Like so:
... Style[ Dynamic @ HalfPlane[...

A second small issue... does anyone know how I could add the degree symbol to the label of the slider?

You can provide your controller layout explicitly, e.g.:
Control[
  {{a1, 30, "θ"}, 0, 360, Row[{Slider[##], Spacer[5], #, Degree}] &}
]


Alternate routes to travel from Houston International airport to Lafayette, Louisiana

Question: I have a flight reaching Houston International airport at 14:00 hrs. I have a connecting flight within 1hr and 30 mins. If I miss this flight due to immigration and customs delay, I would like to know the cheapest means to travel to Lafayette from Houston International airport?Are there any alternate routes?
Comment: If you miss your connecting flight because of a customs or immigration delay the carrier is responsible for rebooking you. It is a good idea to know your options before you arrive at the the ticket desk for rebooking but they should put you on the next plane.
Comment: If you can hitch a ride...  There's a reasonable amount of private craft flying from Houston EFD to Lake Charles LCH and nearby spots if that's of any use.
Comment: As I already told you previously, your airline will simply place you on the next flight, of which there are many. And you're unlikely to miss the connection anyway.
Answer: Given you've said that this is a connecting flight I'm presuming that both flights are on the same ticket.
If you miss the connecting flight, even if it's due to delays in customs and immigration, then the airline will change you to a later flight at no cost.  Simply go to the customer service desk at the connecting airport and they will look after you.
If the next flight is the following day, and the problem wasn't their fault (eg, the inbound aircraft wasn't delayed) then any additional costs such as hotels will be your responsibility.  If the inbound flight was delayed then they may or may not offer to cover a hotel/meals depending on the specific circumstances.
Even if the flights were booked on separate tickets it's worth checking with the airline to see if they will re-accommodate you on a later flight.  For example, United Airlines has a "flat tyre" policy that as long as you arrive at the check-in counter within 2 hours of your flight departing they will attempt to put you on a later flight at no charge.
Comment: I enquired with Lufthansa customer care and they informed me that it won't be their responsibility if I miss the flight due to immigration and customs delays. So I am preparing for an alternate plan if things don't move smoothly
Answer: Rome2Rio shows three alternatives to flying: bus, train, and car. The bus is a Greyhound service that takes 4h43. It departs from Houston city though so you'll have to find a way to get to the bus terminal. The train is an Amtrak service that takes 5h06. It too departs from Houston city and will require you to find a way to get to the train station. Finally you could rent a car and drive, of course.
Comment: Note that the train service is very limited:  [three trains per week,](http://www.amtrak.com/ccurl/671/71/Sunset-Limited-Schedule-030815.pdf) on Tuesdays, Fridays, and Sundays.  It's also a long haul train;  it starts in Los Angeles and has been travelling for a day and a half by the time it gets to Houston.  Such trains are chronically late in the USA.


Migrate CiviCRM from Joomla to Wordpress

Question: I don't even know where to start. I have been tasked with migrating an older version of CiviCRM (3.4.8) on Joomla 1.5 to a newer version of CiviCRM on Wordpress. I got a fresh install of CiviCRM done on Wordpress 4.4, but I'm not sure where to go from here. I'm not familiar with Joomla (this is not my website), so please be very specific. I need everything (users, customizations, whatever else) moved over without having to delete anything on the current site.
Answer: In case it helps anyone, this is what I did:
Initial set-up:
- a working Joomla site, with Civicrm and Joomla tables in the same database
- a separate installation of Wordpress on the same server (articles and static content already imported from the Joomla site and redirects set up as required)
Aim: migrate the Joomla Civicrm tables and data to the Wordpress installation. In this case we chose to do it without moving the Civicrm tables, for simplicity.
Result: Wordpress tables and Civicrm tables are in two separate databases

Backup Joomla Civicrm tables or the whole database.
Make a note of:

Civicrm version number in Joomla Civicrm
what components and extensions you have installed in Joomla Civicrm
any user permissions in Joomla Civicrm (if you use permissions).

Install Civicrm in Wordpress (check version is same as Joomla Civicrm).
Install/remove Civicrm components to match the Joomla Civicrm.
Install any Civicrm extensions (check versions) to match Joomla Civicrm.
Export data (should be just one row) from Wordpress Civicrm table civicrm_uf_match. Disable foreign key checks just in case.
In the Joomla Civicrm database, make a copy of table civicrm_uf_match (in case you need to revert to Joomla).
In the Joomla Civicrm database, truncate the table civicrm_uf_match and import the data exported from Wordpress Civicrm table. Preferably disable foreigh key checks.
Edit the Wordpress civicrm.settings.php file (by default it's in wp-content/uploads). Change CIVICRM_UF_DSN and CIVICRM_DSN to point to the Joomla database.
I also edited the row 'userFrameworkUsersTableName' in the table civicrm_setting, to change joomla-table-prefix_users to wp-table-prefix_users, but I don't know if this is necessary.
You should now be able to access the 'old' Civicrm tables through Wordpress.
Civicrm->Administer->Users and permissions->Synchronise Users to Contacts

That's it. There's a bit of tidying up to do (see below), but at this stage you can still easily revert to Joomla if necessary by replacing the table civicrm_uf_match with the copy, and by reversing steps 9 and 10.

Tidy up: manually set up Civicrm user permissions to correspond to the old Joomla setup. Add any missing users. I had already used the FG Migrate Joomla to Wordpress plugin to migrate users and articles from Joomla.
Tidy up: drop all the Joomla tables (and any other non-civicrm tables) from the Joomla database.
Tidy up: drop the civicrm tables from the Wordpress database.

Comments/corrections welcome.
Answer: For the question about Joomla (users and permission), ask the wordpress or joomla communities.
For the migration of civicrm itself, it should be fairly easy: just copy the civicrm database (or the tables civicrm_* if they are in the same database than the joomla site)
Check on civicrm.settings.php see if you have a mention of joomla and replace it by wordpress and you should be almost there
You might have to manually change how the drupal users are mapped to the civicrm contacts, unless you do manage to keep the same ids for joomla and civi
Answer: Re: civicrm.settings.php mentioned above, since you installed from WP, you shouldn't need to worry about Joomla there.  What version of CiviCRM did you install in WP, the latest? If so, the schema has changed a good bit from 3.4.8!  It might be best if you can update/upgrade CiviCRM to * (whatever version you are asked to use) in (a copy of) the Joomla site, and only afterwards, move your CiviCRM database into the WP- civicrm one.  The upgrade can take some time, and present its own challenge.
  There's a table in CiviCRM  syncing WP defined users and CiviCRM users, civicrm_uf_match.  The users should exist as 'contacts' in civicrm, and the email address is the uf_name, or identifier, used to match users in WP and CiviCRM. If you have already created users or data in the 'new' CiviCRM database with WP, save that database and, after you do the upgrade, try changing the connection info/credentials in the WP install to point to it.
Go to 'CiviCRM' from WP (it looks like another plugin) and the user data should automatically get synced, you can verify by looking at the uf_match table.


Can't delete 'cloud calendar' from my iPhone

Question: I have an iPhone 5 with iOS 8.1.2 and I cannot delete a cloud calendar.  When I edit and go to the calendar all I get is the name of the calendar and the color that represents it.  No delete button at the bottom.  In fact, nothing below the colors.  Has anyone had this issue and are there any solutions short of a reset?
Comment: Welcome to Ask Different! Whilst the device model and iOS version are useful information, the title to your question should be as descriptive as possible regarding what the *problem* is that you are facing. I've edited the title to explain what I believe the actual problem is, but feel free to edit further.
Answer: Subscribed Calendar can't be deleted directly from the Calendar app.
Go to Settings → Mail, Contacts, Calendars and you can unsubscribe from it.
Sometimes subscribed calendars on OS X can't be deleted on iOS.
Comment: I attempted the Mail, Contacts, Calendars solution and I found where I have one subscribed calendar and I am actually using that one.  The one I'm trying to remove says subscribed but doesn't show up there.  In fact the only place it shows up is in the calendars tab within the open app. It doesn't show up on my iPad or MacBook Pro, just on the iPhone so I don't know the source to attempt deleting at that point.
Comment: Dose this subscribed Calendar belongs to iCloud group?


Making a curved tube thinner or thicker without scaling its overall size

Question: Is there a simple way to change the thickness/diameter of a curved tube without scaling its overall size?
E.g. scaling the minor radius of an already created torus without affecting its major radius or change the bevel width of a curve that has already been converted to a mesh.
Answer: Yes, in edit mode you can use Alt+S to scale along vertex normals instead of from the median point.
So you can scale this...

To this...

To this...

This also works for bezier curves as well, even without converting to mesh.
Comment: Wow, that is such a useful feature!
Comment: This isn't working as pictured here for me. Alt + S tends to want to scale a torus into an eye shape.
Comment: @user2867288  Make sure your pivot point is not set to 3D cursor or something like that.
Comment: Just wanted to add that this is the shrinken/flatten tool you can find in the sidebar, too.
Answer: FYI:  in more-recent versions of Blender, suggestion #1 is simply available by a "Shrink/Fatten" button on the tool pane when in Edit mode.  (It is equivalent to Alt+S, as it indicates.)
Answer: Try the following method.

Change Mesh Select Mode to Edge
Select Edge Ring
Select Edge Loop
Change Pivot Point to Individual origins
Scale

This may seem a rather tedeous procedure, but can be used on tube with ends.
Let's go through this on the mesh below.

1. Change Mesh Select Mode to Edge
Aim: To select edge loops individually.
hotkeys: Ctrl-Tab -> E

2. Select Edge Ring
Aim: Select one edge for each edge loops.
Hotkeys: Ctrl-Alt-RMB on one of the edges

3. Select Edge Loop
Aim: Select all edge loops.
Hotkeys: Ctrl-E -> P
Caution: Alt-RMB is usually used for edge loop select but cannot be for this method.

4. Change Pivot Point to Individual orignis
Aim: Manipulate each edge loop individually.
Hotkeys: Ctrl-Period

5. Scale
Aim: Change Size
hotkeys: S
Answer: Just add the solidify modifier(Modifiers tab>Add Modifiers>Solidify)
Adjust the thickness.
If you have a limited poly count just delete the internal mesh.


How to sync original bpm of an mp3 file to the bpm of my drum module?

Question: I start by creating a drum loop or a percussion loop in Acoustica Mixcraft at a specified bpm. I turn into an mp3 file, store it on a usb, connect the usb to my Roland TD-30 Module and play it as a song. I would like to play the drums along with the percussion loop using the internal click, set at the very same bpm. The internal bpm is ALMOST in synch with the tempo of the mp3 file but unfortunately not entirely. At the end of the song you start to hear that they are out of synch. It isn't much, but enough to hear the difference, and hence it will not work. I can adjust the speed of the song (the mp3 file) but only in percentage units and one single percentage unit would be too much. How could this be solved?
Comment: can you not set the bpm when you start creating the loop, then match the same bpm on the click track by entering it?
Comment: Is the song in the mp3 at a constant tempo? If it's not, you'll need to adjust it to be constant using something like Live's warp.
Answer: I know you wanted to avoid it, but it sounds like any solution may be far more trouble than its worth, so just go with a click on the actual loop.
But if you definitely want it in sync with the internal click I would try these out...

Use a midi out from your drums, set its clock to master. Midi in to your DAW, set clock to external. Set the bpm you want on your drums and then make the tracks using the drums clock as a control
Midi cable from your computer to your drums, headphones into your drums, play the midi sequence in your DAW and you can hear it on your drums. Then export a midi file not a song
Comment: If there is some reason you cannot connect your DAW to your TD-30, and you are restricted/committed to plugging in a USB drive with an audio file on it, perhaps try a different (lossless) encoding like .wav.
Answer: Quick and dirty solution: record your MP3 twice, once with a click, once without. Use the version with a click, instead of the drum module's internal click.
More technical solution: synchronise your drum module's tempo with your DAW using MIDI.