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  • What is the cost of memory access?

    - by Jurily
    We like to think that a memory access is fast and constant, but on modern architectures/OSes, that's not necessarily true. Consider the following C code: int i = 34; int *p = &i; // do something that may or may not involve i and p {...} // 3 days later: *p = 643; What is the estimated cost of this last assignment in CPU instructions, if i is in L1 cache, i is in L2 cache, i is in L3 cache, i is in RAM proper, i is paged out to an SSD disk, i is paged out to a traditional disk? Where else can i be? Of course the numbers are not absolute, but I'm only interested in orders of magnitude. I tried searching the webs, but Google did not bless me this time.

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  • How to Parse 'Mathy' Stuff...

    - by Rob P.
    Please forgive my title, I really don't know how to phrase it better. This isn't a school assignment or anything, but I realize it's a mostly academic question. But, what I've been struggling to do is parse 'math' text and come up with an answer. For Example - I can figure out how to parse '5 + 5' or '3 * 5' - but I fail when I try to correctly chain operations together. (5 + 5) * 3 It's mostly just bugging me that I can't figure it out. If anyone can point me in a direction, I'd really appreciate it.

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  • dynamic detail section using user date range

    - by user1437828
    I have a particular report that I need help with. I have an assignment where we are looking for missing data for a particular date - the situation is that users are required to enter a begin and an end note for their shift and their shift is either a day shift or a night shift. So within a 24 hour period there should be a day begin note, day end note, evening begin note and an evening end note I have the command written to generate the required data for ONE DAY ONLY using a BeginDate parameter supplied by the user What I need is to allow the user to enter a date range (add another parameter EndDate), then evaluate the data entry (command) for each day. The parameter being passed in using the user's input is a date and in the Group Expert the user input is not an available field Any help or suggestions would be most appreciated!

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  • How to compute power spectrum from 2D FFT

    - by user1452954
    I've encounter a problem when doing my lab assignment, not sure how to implement this: Use fft2 on a gray image and to do Fourier transform and then compute the power spectrum. This is my code so far: >> Pc = imread('pckint.jpg'); >> whos Pc; Name Size Bytes Class Attributes Pc 256x256 65536 uint8 >> imshow(Pc); >> result = fft2(Pc); My question is from the result. How to computer power spectrum?

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  • Random walk- Brownian Motion

    - by Sam
    I've been assigned the project of creating a simple console app. that models brownian motion in a 2D plane. I wasn't given much information on how to do so (and I'm hoping that it's a pretty popular assignment so that I could get some insight) just that it relies on random number generation. I researched brownian motion for a little bit and saw some formulas that looked complicated, but by the description is just seems to have to move randomly within a certain number interval. Can anyone clarify? Am I to create a program that continually creates a random number in an interval and then modify the particles "x" and "y" coordinate or is there more to it? Thanks for any help.

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  • ASP MVC Creating Form Rows Dynamically

    - by Jonathan Stowell
    Hi Guys, I haven't even attempted this yet and am creating this question for advice really. I have a strongly typed page which receives a form model composed of several components. It is to create a mitigating circumstance (MC) for a student at a university for my final year project. A MC can be composed of the initial problem, assessment extensions, and I use a multi select box to allow the user to select staff retrieved from the database which are able to view the MC once created. The thing is I feel that a student could be granted many assignment extensions for one problem. I am wander if it is possible to include a button/image on the form which when clicked will create a new assessment extension object, and duplicate the form components to set the values for the object? This would all need to occur without any page refreshes. Any advice, or links to good tutorials would be appreciated. I have so far been unable to find any suitable examples. Thanks, Jon

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  • Is it possible to access the line of code where a method is called from within that method?

    - by Dan Tao
    Disclaimers: I am not interested in doing this in any real production code. I make no claim that there's a good reason why I'm interested in doing this. I realize that if this is in any way possible, it must involve doing some highly inadvisable things. That said... is this possible? I'm really just curious to know. In other words, if I have something like this: int i = GetSomeInteger(); Is there any way from within GetSomeInteger that the code could be "aware of" the fact that it's being called in an assignment to the variable i? Again: no interest in doing this in any sort of real scenario. Just curious!

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  • if (self = [super init]) vs. if ((self = [super init]))

    - by JOM
    Was just doing a code review and started to wonder: I thought if (self = [super init]) checks whether assigning return value of [super init] to variable self was successful or not (value of operation). Thus (self = nil) would actually be TRUE. I thought if ((self = [super init])) checks what is the value of self after assignment (value of variable). Thus ((self = nil)) would be FALSE. Which one is the correct way to use when initializing your own classes? Apple documentation uses the former one (for example here), which style I'm actually using now.

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  • Introduction to c# for c/c++ users

    - by Ronny
    I have 6+ years of c/c++ experience. Tomorrow starts a university assignment where I will have to use c#. Therefor I would like to have a list of links which you think important, an extensive tutorial - in short everything you think worthy. codingstyle, best practices, ... (I don't know any specifics about the c# environment I will be using(IDE, OS, w/e), the first meeting is tomorrow evening) (I have never coded c# before) One more thing: I would like to work using linux (kubuntu 10.4). IDE / environment / turorial suggestions regarding linux specifically are very welcome. thanks for your help!

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  • How to clone a model's attributes easily?

    - by Zabba
    I have these models: class Address < ActiveRecord::Base belongs_to :event attr_accessible :street, :city validates :street, :city, :presence => true end class Event < ActiveRecord::Base has_one :address accepts_nested_attributes_for :address end If I do the below assignment in the Events create action and save the event I get an error: #Use the current user's address for the event @event.address_attributes = current_user.address.attributes #Error occurs at the above mentioned line ActiveRecord::RecordNotFound (Couldn't find Address with ID=1 for Event with ID=) I think what's happening is that all the address's attributes (including the primary key) is getting assigned in the @event.address_attributes = line. But all I really want is the "real data" (street, city), not the primary keys or created_at etc to get copied over. I suppose I could write a small method to do this sort of selective copy but I can't help but feel there must be some built-in method for this? What's the best/right way to do this?

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  • Highest value datatype can store in c#

    - by user472832
    I am writing a small program for my assignment to find the primitive roots of a prime number. So far, the program works for smaller prime numbers till 13 and gives correct number of roots. But for higher primes numbers, it is showing only fewer primitive roots. And now i got stuck for the prime number 41, shows no primitive roots for it. I used DOUBLE datatype for the calculation, and again tried with the datatype DECIMAL, but no luck. Does anyone know about this kind of problem??? Thank you.

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  • Policies Array Class-Design wrapper

    - by PT
    Hi, i want to write an wrapper for different Array Classes with different Policies. For example: typedef ArrayType<useValArray,StdAllocator> Array; // one global assignment I want to use the class like a blitz++ Array for example: Array<double,2> x(2,2); //maps the Array to an Valarray or to a Blitz++ Array Array<double,2> x2(5,6); is this Posible? Which technics i need to realise that?

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  • is the + in += on a Map a prefix operator of =?

    - by Steve
    In the book "Programming in Scala" from Martin Odersky there is a simple example in the first chapter: var capital = Map("US" -> "Washington", "France" -> "Paris") capital += ("Japan" -> "Tokyo") The second line can also be written as capital = capital + ("Japan" -> "Tokyo") I am curious about the += notation. In the class Map, I didn't found a += method. I was able to the same behaviour in an own example like class Foo() { def +(value:String) = { println(value) this } } object Main { def main(args: Array[String]) = { var foo = new Foo() foo = foo + "bar" foo += "bar" } } I am questioning myself, why the += notation is possible. It doesn't work if the method in the class Foo is called test for example. This lead me to the prefix notation. Is the + a prefix notation for the assignment sign (=)? Can somebody explain this behaviour?

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  • Javascript Pointers question with Dates

    - by Mega Matt
    I noticed this situation in my code (unfortunately), and was able to duplicate it in my own JS file. So I have this code: var date1 = new Date(); // today var date2 = date1; date2 = date2.setDate(date2.getDate() + 1); // what is date1? After this code executes, date1 is today's date + 1! This harkens back to my undergrad days when I learned about pointers, and I guess I'm a little rusty. Is that what's happening here? Obviously I've moved the assignment away from date1, and am only modifying date2, but date1 is being changed. Why is this the case? Incidentally, after this code executes date2 is a long number like 1272123603911. I assume this is the number of seconds in the date, but shouldn't date2 still be a Date object? setDate() should return a Date object... Thanks for the help.

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  • MySQL - accessing a table sum and compare to another table?

    - by assignment_operator
    This is for a homework assignment. I just plain don't understand how to do it. The instructions for this particular question is: List the branch name for all branches that have at least one book that has at least 4 copies on hand. Where the tables in question are: Branch: BranchName | BranchId Henry Downtown | 1 16 Riverview | 2 Henry On The Hill | 3 Inventory: BookId | BranchId | OnHand 1 | 1 | 2 2 | 3 | 4 3 | 1 | 8 4 | 3 | 1 5 | 1 | 2 6 | 2 | 3 From what I understand, I can get the number of OnHand per branch name with: SELECT BranchName, SUM(OnHand) FROM Branch B, Inventory I WHERE B.BranchId = I.BranchId GROUP BY BranchName; but I don't get how I'd do the comparison between the sum of OnHand per branch and 4. Any help would be appreciated, guys!

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  • Is it possible to use the values method for a HashMap if the values are ArrayLists?

    - by Denman
    I'm stuck trying to get something to work in an assignment. I have a HashMap<Integer, ArrayList<Object>> called sharedLocks and I want to check whether a certain value can be found in any ArrayList in the HashMap. The following code obviously wouldn't work because Object[] can't be cast to ArrayList[], but it is a demonstration of the general functionality that I want. ArrayList[] values = (ArrayList[]) sharedLocks.values().toArray(); boolean valueExists = false; for (int i = 0; i < values.length; i++) { if (values[i].contains(accessedObject)) { valueExists = true; } } Is there a way for me to check every ArrayList in the HashMap for a certain value? I'm not sure how to use the values method for HashMaps in this case. Any help would be much appreciated.

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  • What do we call this?

    - by shinkou
    I'm wondering what do we call this kind of assignment. <?php class SimpleClass { public $var1; public $var2; public $var3; public function SimpleClass() { $this->var1 = 'one'; $this->var2 = 'two'; $this->var3 = 'three'; } } function test() { $objSc = new SimpleClass(); $objSc->var4 = 'WTF?!'; # <-- what do we call this? var_dump($objSc); } test(); ?> Better with references or links. Thanks in advance!

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  • nested list comprehension using intermediate result

    - by KentH
    I am trying to grok the output of a function which doesn't have the courtesy of setting a result code. I can tell it failed by the "error:" string which is mixed into the stderr stream, often in the middle of a different conversion status message. I have the following list comprehension which works, but scans for the "error:" string twice. Since it is only rescanning the actual error lines, it works fine, but it annoys me I can't figure out how to use a single scan. Here's the working code: errors = [e[e.find('error:'):] for e in err.splitlines() if 'error:' in e] The obvious (and wrong) way to simplify is to save the "find" result errors = [e[i:] for i in e.find('error:') if i != -1 for e in err.splitlines()] However, I get "UnboundLocalError: local variable 'e' referenced before assignment". Blindly reversing the 'for's in the comprehension also fails. How is this done? THanks. Kent

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  • C++0x: how to get variadic template parameters without reference?

    - by Sydius
    Given the following contrived (and yes, terrible) example: template<typename... Args> void something(Args... args) { std::tuple<Args...> tuple; // not initializing for sake of example std::get<0>(tuple) = 5; } It works if you call it like so: int x = 10; something<int>(x); However, it does not work if you call it like this: int x = 10; something<int&>(x); Because of the assignment to 5. Assuming that I cannot, for whatever reason, initialize the tuple when it is defined, how might I get this to work when specifying the type as a reference? Specifically, I would like the tuple to be std::tuple<int> even when Args... is int&.

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  • Feedback + Bad output

    - by user1770094
    So I've got an assignment I think I'm more or less done with, but there is something which is messing up the output badly somewhere down the line, or even the calculation, and I don't see where the problem is. The assignment is to make a game in which a certain ammount of players run up through a tunnel towards a spot,where they will stop and spin around it,and then their dizziness is supposed to make them randomly either progress towards goal or regress back towards start.And each time they get another spot closer to goal,they get another "marking",and it goes on like this until one of them reaches goal. The program includes three files: one main.cpp,one header file and another cpp file. The header file: #ifndef COMPETITOR_H #define COMPETITOR_H #include <string> using namespace std; class Competitor { public: void setName(); string getName(); void spin(); void move(); int checkScore(); void printResult(); private: string name; int direction; int markedSpots; }; #endif // COMPETITOR_H The second cpp file: #include <iostream> #include <string> #include <cstdlib> #include <ctime> #include "Competitor.h" using namespace std; void Competitor::setName() { cin>>name; } string Competitor::getName() { return name; } void Competitor::spin() { srand(time(NULL)); direction = rand()%1+0; } void Competitor::move() { if(direction == 1) { markedSpots++; } else if(direction == 0 && markedSpots != 0) { markedSpots--; } } int Competitor::checkScore() { return markedSpots; } void Competitor::printResult() { if(direction == 1) { cout<<" is heading towards goal and has currently "<<markedSpots<<" markings."; } else if(direction == 0) { cout<<"\n"<<getName()<<" is heading towards start and has currently "<<markedSpots<<" markings."; } } The main cpp file: #include <iostream> #include <string> #include <cstdlib> #include <ctime> #include "Competitor.h" using namespace std; void inputAndSetNames(Competitor comps[],int nrOfComps); void makeTwist(Competitor comps[],int nrOfComps); void makeMove(Competitor comps[],int nrOfComps); void showAll(Competitor comps[],int nrOfComps); int winner(Competitor comps[],int nrOfComps, int nrOfTwistPlaces); int main() { int nrOfTwistPlaces; int nrOfComps; int noWinner = -1; int laps = 0; cout<<"How many spinning places should there be? "; cin>>nrOfTwistPlaces; cout<<"How many competitors should there be? "; cin>>nrOfComps; Competitor * comps = new Competitor[nrOfComps]; inputAndSetNames(comps, nrOfComps); do { laps++; cout<<"\nSpin "<<laps<<":"; makeTwist(comps, nrOfComps); makeMove(comps, nrOfComps); showAll(comps, nrOfComps); }while(noWinner == -1); delete [] comps; return 0; } void inputAndSetNames(Competitor comps[],int nrOfComps) { cout<<"Type in the names of the "<<nrOfComps<<" competitors:\n"; for(int i=0;i<nrOfComps;i++) { comps[i].setName(); } cout<<"\n"; } void makeTwist(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].spin(); } } void makeMove(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].move(); } } void showAll(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].printResult(); } cout<<"\n\n"; system("pause"); } int winner(Competitor comps[],int nrOfComps, int nrOfTwistPlaces) { int end = 0; int score = 0; for(int i=0;i<nrOfComps;i++) { score = comps[i].checkScore(); if(score == nrOfTwistPlaces) { end = 1; } else end = -1; } return end; } I'd be grateful if you would point out other mistakes if you see any.Thanks in advance.

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  • Can a method return an NSRange?

    - by Dan Donaldson
    I have a method that returns an NSRange. When I call this method from outside the class I get a compile error. NSRange tmpRange; tmpRange = [phrase rangeInString:searchString forString:theLetter goingForward:YES]; return tmpRange.location == -1; in the .h file: #import <Foundation/Foundation.h> @interface Phrase : NSObject { } - (NSRange) rangeInString:(NSString *) tgt forString:(NSString *) find goingForward:(BOOL) fwd; @end This method is called within the Phrase object by other methods without problems. The compiler says 'incompatible types in assignment'. Can anyone explain this to me? I assume it has to do with returning an NSRange/struct type value generated outside the object, but I don't know why it works in one place and not the other.

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  • Assigning a pointer variable to a const int in C++?

    - by John
    I'm wondering if anyone can explain the following to me: If I write int i = 0; float* pf = i; I get a compile error (gcc 4.2.1): error: invalid conversion from ‘int’ to ‘float*’ Makes sense - they are obviously two completely different types. But if instead I write const int i = 0; float* pf = i; It compiles without error. Why should the 'const' make a difference on the right hand side of the assignment? Isn't part of the idea of the 'const' keyword to be able to enforce type constraints for constant values? Any explanation I have been able to come up with feels kind of bogus. And none of my explanations also explain the fact that const int i = 1; float* pf = i; fails to compile. Can anyone offer an explanation?

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  • Python os.path.walk() method

    - by Aaron Moodie
    I'm currently using the walk method in a uni assignment. It's all working fine, but I was hoping that someone could explain something to me. in the example below, what is the a parameter used for on the myvisit method? >>> from os.path import walk >>> def myvisit(a, dir, files): ... print dir,": %d files"%len(files) >>> walk('/etc', myvisit, None) /etc : 193 files /etc/default : 12 files /etc/cron.d : 6 files /etc/rc.d : 6 files /etc/rc.d/rc0.d : 18 files /etc/rc.d/rc1.d : 27 files /etc/rc.d/rc2.d : 42 files /etc/rc.d/rc3.d : 17 files /etc/rc.d/rcS.d : 13 files

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  • Two phase Construction in C++

    - by tommieb75
    I have as part of assignment to look into a development kit that uses the "two-phase" construction for C++ classes: // Include Header class someFubar{ public: someFubar(); bool Construction(void); ~someFubar(); private: fooObject _fooObj; } In the source // someFubar.cpp someFubar::someFubar : _fooObj(null){ } bool someFubar::Construction(void){ bool rv = false; this->_fooObj = new fooObject(); if (this->_fooObj != null) rv = true; return rv; } someFubar::~someFubar(){ if (this->_fooObj != null) delete this->_fooObj; } Why would this "two-phase" be used and what benefits are there? Why not just instantiate the object initialization within the actual constructor?

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  • define macro in C wont work

    - by Spidfire
    Im trying to make a macro in C that can tell if a char is a hex number ( 0-9 a-z A-Z) #define _hex(x) (((x) >= "0" && (x) <= "9" )||( (x) >= "a" && (x) <= "z") || ((x) >= "A" && (x) <= "Z") ? "true" : "false") this what ive come up with but it wont work with a loop like this char a; for(a = "a" ; a < "z";a++){ printf("%s => %s",a, _hex(a)); } but it gives a error test.c:8: warning: assignment makes integer from pointer without a cast test.c:8: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer

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