For a particular design, I need to take an unregulated voltage from a battery and regulate 5 different DC voltages from it. What's worse is that I need step-up and step-down converters. What's even worse is that some voltages need more current than others.  Note: To clarify the question, I've given the specific voltages that I need. However, keep in mind that I'm wondering what to do in general, not just this specific case.  The battery voltage is 11.1 V, which drops as it discharges. I need to create:   15 V 12 V 5.5 V 5.0 V 3.3 V   The 12 V level needs to run at least 1 A, and the three lowest need to run about 200 mA each. The 15 V level doesn't use more than 50 mA.  So this is my question: would it be better to go from the battery to 15 V to 12 V to 5.5 V to 5.0 V to 3.3 V, or would it be better to just connect all 5 regulators directly to the battery?
Sorry if this is a stupid question, but I am mainly working with 5V PIC circuits and now want to integrate a component (nRF24l01+) that needs a 3.3V supply.  As I have a box full of ~7V wall-warts, I normally use a 7805 or similar LDO regulator to power the circuit. Now I want to also get 3.3V without using a separate external supply.  I'm looking for guidance on the "right" way to do this. I think the options are:   Use a voltage divider on the output of my 5V regulator to get 3.3V Use a 3.3V LDO regulator fed directly from the 7V wall-wart   Use the output of the 5V regulator as input to a 3.3V regulator   I can see that all of these would work (would they?) and that option 3 seems to waste least power, but I don't know what gotchas might arise by chaining two regulators like this.  What things do I need to consider when making this choice?
What is the difference between \big[ (or equivalently \big() and \bigl[? Is it always necessary to mention l (left) and r (right)? I'm looking for an answer considering both technical limitations and user experience.   Does it need a reload from a technical standpoint? Assume you have a flat table that stores an ordered tree hierarchy:  Id   Name         ParentId   Order  1   'Node 1'            0      10  2   'Node 1.1'          1      10  3   'Node 2'            0      20  4   'Node 1.1.1'        2      10  5   'Node 2.1'          3      10  6   'Node 1.2'          1      20   Here's a diagram, where we have [id] Name.  Root node 0 is fictional.                          [0] ROOT                           /    \                [1] Node 1          [3] Node 2               /       \                   \     [2] Node 1.1     [6] Node 1.2      [5] Node 2.1           /            [4] Node 1.1.1   What minimalistic approach would you use to output that to HTML (or text, for that matter) as a correctly ordered, correctly indented tree?   Assume further you only have basic data structures (arrays and hashmaps), no fancy objects with parent/children references, no ORM, no framework, just your two hands. The table is represented as a result set, which can be accessed randomly.   Pseudo code or plain English is okay, this is purely a conceptional question.  Bonus question: Is there a fundamentally better way to store a tree structure like this in a RDBMS?    EDITS AND ADDITIONS  To answer one commenter's ('s) question: A root node is not necessary, because it is never going to be displayed anyway. ParentId = 0 is the convention to express "these are top level". The Order column defines how nodes with the same parent are going to be sorted.  The "result set" I spoke of can be pictured as an array of hashmaps (to stay in that terminology). For my example was meant to be already there. Some answers go the extra mile and construct it first, but thats okay.  The tree can be arbitrarily deep. Each node can have N children. I did not exactly have a "millions of entries" tree in mind, though.  Don't mistake my choice of node naming ('Node 1.1.1') for something to rely on. The nodes could equally well be called 'Frank' or 'Bob', no naming structure is implied, this was merely to make it readable.  I have posted my own solution so you guys can pull it to pieces. In class we are currently covering upper/lower bounds, big Oh and omega and the like. I am pretty good on the "typical" functions one would do, but at a complete loss at "general" statements. This ons function, for example:  $$\forall f\in\mathcal{F}: \lfloor \sqrt{\lfloor f(n)\rfloor }\rfloor \in O(\sqrt{f(n)}).$$  the domain F by the same is all natural numbers that return a real positive number when inputted. My first instinct with something like this is to remove the floors, the general strategy I though to solve this is remove the outer floor, then get rid of the square root, and then the inner floor. But I have no idea how to go about this or if this is even the right way to do it.  Help please? Thanks in advance. LINQ's Distinct() on a particular property Where To start Learning With Salesforce Development Where should I start learning? There are various topics to learn like Objects, Classes, Apex, Visualforce, SOSL, SOQL, Triggers, etc. There are so many options out there to start learning. I couldn't decide what topic to learn first, and then step by step get proficiency in all aspects of Saleforce. I am having trouble getting onto a server in Minecraft PE on iOS. When I tap on the person's server it just says invalid name:    I have tried turning off and restarting the iPad, going to home screen and logging back into the server but I have had no luck and no change. Is there a reason why this is so? How can the Anomalous Expansion of Water from 4$^\circ$C to 0$^\circ$C be explained with reference to subatomic particles? How to reference generic classes and methods in xml documentation White stains and stainless steel cookware I know this question has been asked before in some form or another, but I can't seem to find a definitive answer. I've looked on SA, chowhound, martha stewart, about.com, etc., and answers seem to vary. Answers that I've seen vary from using vinegar to washing using special stainless steel soaps (which I'm not very keen on using) to only using soft sponges and hot water.   The one thing I always do is wash my stainless steel with warm soapy water and a soft sponge. If there's burned food stuck on the cookware, I scrape it off with a wood pot scraper (lightly, of course). And I always dry with a soft cloth immediately after washing. Yet I still get stains!  I'd like to get a general consensus on how to prevent those white and rainbow colored stains as well as minimizing corrosion. sudo -k vs. sudo -K I know what the man page has to say about the -K and -k :     ‑K       The ‑K (sure kill) option is like ‑k except that it removes the user's   cached credentials entirely and may not be used in conjunction with a   command or other option. This option does not require a password. Not   all security policies support credential caching.      ‑k[command]       When used alone, the ‑k (kill) option to sudo invalidates the user's   cached credentials. The next time sudo is run a password will be   required. This option does not require a password and was added to   allow a user to revoke sudo permissions from a .logout file. Not all   security policies support credential caching. When used in conjunction   with a command or an option that may require a password, the ‑k option   will cause sudo to ignore the user's cached credentials. As a result,   sudo will prompt for a password (if one is required by the security   policy) and will not update the user's cached credentials.   So if there is no need to use a command in conjunction with these options, am i correct in assuming K is always the better option to use rather that k? In Back to the Future, how did Marty get the timing right with the lightning strike? So, in the first movie, presumably the Doc and Marty know exactly when the lightning will strike the clock tower. This is because Marty has the flyer with the picture of the stopped clock on it. In order to power the DeLorean, the Doc cooks up this contraption to conduct the lightning through a hook into the DeLorean. All Marty has to do is be driving at 88 mph and hit the wire at the exact right moment.  Here's the question though - if you recall, the Doc sets a timer and tells Marty to drive back to a pre-designated starting point. When the timer goes off, Marty is supposed to accelerate to 88 mph. My assumption is that the Doc has calculated the maximum acceleration of the DeLorean, and using this value has determined the exact starting point that the car needs to be at in order to hit the lightning at the right time.  Unfortunately, the car stalls. It takes Marty a while, but he's finally able to start it up. Being that he started late though...shouldn't he have missed the lighting? How do I invoke a Java method when given the method name as a string? If I have two variables:  Object obj; String methodName = "getName";   Without knowing the class of obj, how can I call the method identified by methodName on it?  The method being called has no parameters, and a String return value. It's a getter for a Java bean. How to handle relative urls correctly with a nginx reverse proxy Sure I'm not the first one that tried to serve a domain example.com from a example.net/bbb, but I haven't found a solution yet.  My NGINX configuration follows the  and looks something like this:  server {     listen 80;     server_name example.net;     root /path/to/aaa;      location /bbb/ {         proxy_pass http://example.com/;         proxy_set_header Host $host;         proxy_set_header X-Real-IP $remote_addr;     }      location / {         try_files $uri $uri/ /index.html;     }     location ~ \.(svg|ttf|js|css|svgz|eot|otf|woff|jpg|jpeg|gif|png|ico)$ {         access_log off;         log_not_found off;         expires max;     } }   I can manage to render the root of example.com in example.net/bbb but:  ISSUE 1  example.net/bbb/some/path doesn't work as expected and the index.html of example.net is rendered.  ISSUE 2  Any asset in example.com/assets gives 404 because the browser look for example.net/assets. Be great if I could solve this without placing absolute paths everywhere. Intuition for groups This is quite a non-standard question, certainly for mathematics, though I believe it is no less important (for me and my peers, i.e. grads).  The course I am reading so far introduced us to Groups, rings, fields, etc. in the first year, progressing to characters, reps etc in the latter years.  However, even with representation theory I still don't feel like I have a good intuition.  How do you gain intuition in such an area. I know there will be a response of doing examples, but this doesn't really help - I've done lots already.  Am I doomed. How does one attack a two-time pad (i.e. one time pad with key reuse)? My question might appear the same as the question , but actually I did read all the answers and none of them helped me with the details I need.  I am new to cryptography and my problem is with two time pad attacks on OTP. The problem I had in my course was that I have 10 ciphertexts encrypted with the same key $K$. I am then given another ciphertext that I should decrypt.  I know that XOR-ing two ciphers gives me the XOR of their original messages.  My question is what is the correct thing to do after that?  I tried to take 3 ciphertexts $C_1, C_2$ and $C_3$.  Then get $S_1 = C_1 \oplus C_2  \oplus $' ', also get $S_2 = C_1 \oplus C_3 \oplus$ ' '.  After that I compared all corresponding characters in $S_1$ and $S_2$,  and if $S_1[i] = S_2[i]$ then I calculate $S_1[i] \oplus C_2[i]$ to get $K[i]$.  I tried this on paper before coding and it worked, but I might be missing something.  Is this the right approach? Why does it work? I need to run something as sudo without a password, so I used visudo and added this to my sudoers file:  MYUSERNAME ALL = NOPASSWD: /path/to/my/program   Then I tried it out:  $ sudo /path/to/my/program [sudo] password for MYUSERNAME:    Why does it ask for a password? How can I run/use commands as root with a non-root user, without asking for a password? What is the symbolic significance of the Night King's message? In Game of Thrones S8E1,        Ned Umber is found pinned to a wall by the Night King with a symbolic message, which looks like tentacles coming out of the body of Ned.   Is there some meaning to that symbolic message? If yes, then what is that? How can I change xfce bottom panel to the top? I am using Xubuntu 12.10 and would like to change the panel which is currently on the bootm to the top.  This is the opposite of what most people using Unity want to do.    I have done this in the past but have forgotten how and could not find the info easily this time. Cheers, What is Interface method in salesforce