I'm currently taking differential equations but the guide book (Elementary differential equations and boundary value problems) is aimed for engineers (much like the calculus one from Stewart). I'm looking for a book with the classic mathematical format (definition, theorem, corollary...) and not too much talk or applications.  Thanks
I love R. Courant and F. John's Introduction to Calculus and Analysis because of its wide coverage, precise description and friendly written style.  Are there any classic textbooks like it on ODE/PDE?  thanks.
I've noticed the following happen a few times:   A user posts a question. The question is closed as a duplicate and the usual "Possible Duplicate" links are added at the top. The user promptly removes the duplicate links, even though the question is still closed as a duplicate. (excessive use of list items =P)   Now, I could understand this behavior if there was some dispute about whether or not the question was a duplicate, and the OP were to remove the links and post reasons why they disagree with the closing. However, I've noticed this happening without any attempt to defend the question (such as ).  In my opinion, no one should be allowed to remove the "Possible Duplicate" links as long as the question is still closed as a duplicate. The links should remain for the benefit of the community, so they can navigate to the duplicate questions and either post answers there or read them over and judge if the closing was actually fair. Once/if the question is reopened the links could be edited out if one so chooses.  I guess this is part discussion, part feature request:  Could the "Possible Duplicate" links remain un-editable for as long as the question is still closed? A proof that $1=2$. May I know why it’s false? The entire answer is moving when hovering the bounty button It's just a minor CSS issue. See the following gif: How can I get a reference to a method? Why do you have to use copy_to_user()/copy_from_user() to access user space from the kernel? Is there an easy way to delete an element from an array using PHP, such that foreach ($array) no longer includes that element?  I thought that setting it to null would do it, but apparently it does not work. question about the limit $\lim_{h\to0}\frac{\arcsin(x+h)-\arcsin(x)}{h}$ What is the yield keyword used for in C#? In the  question one of the answers had the following code snippet:  IEnumerable&lt;object&gt; FilteredList() {     foreach(object item in FullList)     {         if(IsItemInPartialList(item))             yield return item;     } }   What does the yield keyword do there?  I've seen it referenced in a couple places, and one other question, but I haven't quite figured out what it actually does.  I'm used to thinking of yield in the sense of one thread yielding to another, but that doesn't seem relevant here. How to avoid interference in wireless communication? I am working on wireless communication system. We are using around 10 pairs of transmitter and receivers. We are using atmega16 microcontroller for encoding and decoding by USART ports.  Now we are able to transmit the data and receive the same in the receiver end, but there is a major problem, when we are finding the 2 transmitter data coming at the same time. The receiver is unable to get it due to interference.  Suppose one transmitter sends "SENDA" at the meanwhile another transmitter sends "GETTS", at that time the receiver can not receive proper data. As all the transmitters and receivers are working in same frequency, so this interference is occurring. How can I resolve this issue? Shipping Labels not received for round trip courier service for UK Visa using VFS Global I purchased the round-trip courier service through VFS Global. In the instructions, it states that you will receive in a separate email the shipping labels for this courier service. I receive Registration Details and Transaction Details only. No Shipping labels. I have called VFS Global in NY,NY and no human being access to ask questions, just an insane phone tree that does not answer my questions on how to get shipping labels that were never sent. I have called the British Consul in Atlanta and she could not answer my questions then transferred me to the same phone tree message that I receive through the British Consulate. I have sent emails to customercare@vfsglobal.com, info.vfsnewyork@vfsglobal.com, NYscanhub.escalate@vfsglobal.com, DLUKVInewyorksensitive@fco.gov.uk and I have received no response from anyone.  Frustrated. I do not know what to do. Please help me!! Find a recurrence relation for the number of ways to arrange $n$ dominoes to fill a $2$ by $n$ checkerboard. I am having trouble with this question, please take a look at it:     Find a recurrence relation for the number of ways to arrange $n$ dominoes to fill a $2$ by $n$ checkerboard.   I have just started reading the topic and it is one of the starting problem. Please help. You can give me some hints, a complete answer is also appreciated.  Thanks How to persistently control maximum system resource consumption on Mac? Before Mavericks, I could use /etc/launchd.conf file to change maximum system resource consumption, for example:  limit maxfiles 16384 unlimited limit maxproc 16384 unlimited   It no longer works in Mavericks.  What is the correct way to do it in the recent version of OS X? This question is updated to request additional answers and details in light of information now available in the Dungeon Master's Guide. In the released DM basic rules, Lost Mine of Phandelver, Hoard of the Dragon Queen, and the DMG teaser there are wands, staves, and rings that you can use to cast spells.  Do abilities that trigger from casting a spell activate when casting a spell from an item?  Can the character modify the spell using class abilities when casting a spell from an item?   Examples include:  An abjurer Wizard's arcane ward recovering hit points from a Dispel Magic cast from a Ring of Spell Storing  A sorcerer using Twinned Spell on a ray of enfeeblement from a Staff of Power  An evocation wizard using Sculpt Spell on a fireball from a Wand of Fireballs.   Now that the DMG is out we have some clearer rules on casting spells from items (DMG p. 141):  Some magic items allow you to cast a spell from the item.  The spell is cast at the lowest possible spell level, doesn't expend any spell slots, and requires no components, unless the item's description says otherwise  The spell uses its normal casting time, range and duration, and the user of the item must concentrate if the spell requires concentration. A magic item, such as certain staffs, may require you to use your own spellcasting ability when you cast a spell from the item.  Does whether or not you can apply class abilities to the casting of the spell depend whether the item uses the user's own spellcasting ability (such as the Staff of Fire) versus an item that comes with a fixed spellcasting ability built-in (such as the Wand of Fireballs)? Does it matter if it's something that triggers more or less automatically like Arcane Ward, versus something you have to control, like Careful Spell? When would you use the Builder Pattern? What are some common, real world examples of using the Builder Pattern?  What does it buy you?  Why not just use a Factory Pattern? The multi-part identifier could not be bound How to redirect stderr and stdout to different files and also display in terminal? I want to see the output of a command in the terminal as if there was no redirection.  Also, stderr needs to be redirected to err.log and stdout needs to be redirected to stdout.log.  It would be nice to also have the exact copy of what is shown in terminal, i.e. errors printed as and when it occurs, in a separate file: stdouterr.log. There are four options. Which of them is correct?- (a)${p\over k}$ (b)${k\over p}$ (c)$\log({p\over k})$ (d)${\log p\over k}$ I somehow want to use the rule for evaluating this kind of sum using integration, i.e. $\int_{0}^{1} f(x) \ dx=\lim_{n\to\infty} {1\over n}\sum_{r=1}^{n}f({r\over n})$  But the given expression $\lim_{n\to\infty} [{1\over kn}+{1\over k(n+1)}+{1\over k(n+2)}+\cdots+{1\over k(n+p-k)}]={1\over k}\lim_{n\to\infty}{1\over n}\sum_{r=0}^{p-k}\frac{1}{1+{r\over n}}$, sum running from $0$ to $p-k$ instead of $n$. So, how to evaluate this limit? Thanks for assistance in advance. Beamer Bibliography Icon I want to list my references in a beamer presentation using thebibliography environment, with the nice little    book icon (\beamertemplatebookbibitems) and  article icon (\beamertemplatearticlebibitems)   in front of each source.  Is there an icon for websites too? something like \beamertemplatewebsitebibitems? If not, is there a way to implement this easily ? How Deep Are Bender's Insides? Bender often pulls large objects from his torso cupboard, but how deep or how much empty space is he capable of storing? Can he bend space around the perimeters of the frame of his torso's door? If that is the case, does it also bend time? I suppose he might bend in more ways than one... String handling by OneHotEncoder I am reading everywhere on new questions and blogs that since version 0.20, OneHotEncoder is able to handle string features. Moreover, the documentation is what looks more ambiguous. Here are the first two lines from the documentation:  Encode categorical integer features as a one-hot numeric array. The input to this transformer should be an array-like of integers or strings, denoting the values taken on by categorical (discrete) features.  First line says it  encodes categorical integer features  and the next line says  input should be array like of integers or strings.  When i tried it, i still got the value error. print(X.columns) encoder = OneHotEncoder(categorical_features=[1,4,5]) encoder.fit(X)  Index(['age', 'sex', 'bmi', 'children', 'smoker', 'region'], dtype='object') ValueError: could not convert string to float: 'female'  I am aware of the means to handle encoding of string features with LabelEncoder, ColumnTransfomer and pd.getDummies() but specifically want to understand about this.