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• Using Python tuples as vectors

  - by Etaoin

  I need to represent immutable vectors in Python ("vectors" as in linear algebra, not as in programming). The tuple seems like an obvious choice. The trouble is when I need to implement things like addition and scalar multiplication. If a and b are vectors, and c is a number, the best I can think of is this: tuple(map(lambda x,y: x + y, a, b)) # add vectors 'a' and 'b' tuple(map(lambda x: x * c, a)) # multiply vector 'a' by scalar 'c' which seems inelegant; there should be a clearer, simpler way to get this done -- not to mention avoiding the call to tuple, since map returns a list. Is there a better option?

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• Calculating 2D angles for 3D objects in perspective

  - by Will

  Imagine a photo, with the face of a building marked out. Its given that the face of the building is a rectangle, with 90 degree corners. However, because its a photo, perspective will be involved and the parallel edges of the face will converge on the horizon. With such a rectangle, is it possible to calculate the angle in 2D of the edges of a face that is 90 degrees to it? In the image below, the blue is the face marked on the photo, and I'm wondering how to calculate the 2D vector of the red lines of the other face:

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• C++ - dynamic pointer of array

  - by Eagle

  Hi to all, first i would like to say i am Newbie in C++. As part of my master thesis i am writing a program in C++ which also get as parameters the variables m and d (both integers). Were d is the power of 2 (this means 2^d elements). Parameter m define the number of possible interactions between one element and the total group (2^d elements). The number of possible interactions is computed as following: \kappa = \sum_{i=0}^m\binom{d}{i} (at present i generate vector of vectors for 2^d x \kappa, but my Prof. would like me to create different statistics to different m's. My first though was to to generate a dynamic array of m arrays of different sizes... Then i though of defining a 3-dim array with the biggest needed 2d array, but also program speed is important (e.g d = 20). i would like to ask for your advice how to define such kind of dynamic array that will also be fast. Regards

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• x86_64 assembler: only one call per subroutine?

  - by zneak

  Hello everyone, I decided yesterday to start doing assembler. Most of it is okay (well, as okay as assembler can be), but I'm getting some problems with gas. It seems that I can call functions only once. After that, any subsequent call opcode with the same function name will fail. I must be doing something terribly wrong, though I can't see what. Take this small C function for instance: void path_free(path_t path) { if (path == NULL) return; free(((point_list_t*)path)->points); free(path); } I "translated" it to assembler like that: .globl _path_free _path_free: push rbp mov rbp, rsp cmp rdi, 0 jz byebye push rdi mov rdi, qword ptr [rdi] call _free pop rdi sub rsp, 8 call _free byebye: leave ret This triggers the following error for the second call _free: suffix or operands invalid for ``call''. And if I change it to something else, like free2, everything works (until link time, that is). Assembler code gcc -S gave me looks very similar to what I've done (except it's in AT&T syntax), so I'm kind of lost. I'm doing this on Mac OS X under the x86_64 architecture.

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• GIS: When and why to use ArcObjects over GDAL programming to work with ArcGIS rasters and vectors?

  - by anotherobject

  Im just starting off with GDAL + python to support operations that cannot be done with ArcGIS python geoprocessing scripting. Mainly I am doing spatial modeling/analysis/editing of raster and vector data. I am a bit confused when ArcObject development is required versus when GDAL can be used? Is there functionality of ArcObjects that GDAL does not do? Is the opposite true too? I am assuming that ArcObjects are more useful in developing online tools versus Desktop analysis and modeling where the difference is more to do with preference? In my case i prefer GDAL because of python support, which I believe ArcObjects lack. thanks!

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• recursive function's summation in MATLAB

  - by lucky

  B=[1 1 1 1 1 1....1] % vector of length N elements Xk= sin(2*pi/16) i need to find function alpha(l,k) which is having two variables l and k and a condition given that alpha(l,0)=alpha(l,-1)=alpha(l,-2)......=alpha(l,-(N-1))=0 i.e no matter what value of l ,alpha = 0 for past values A= input('no of iterations'); % no. of iterations user want N=input('N values of alpha:') alpha1=[]; for k=0:A-1 l=0:N-1 % need 10 separate alpha values for every k, which goes from 0 to A-1 alpha(l,k)= Xk + summation( B(j)*alpha(l,k-j)) % as summation goes from j=1 to N alpha1=[alpha1 alpha] end; could anyone please help me to solve this recursive function, i am new to matlab. alpha

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• How to override ggplot2's axis formatting?

  - by Richie Cotton

  When you choose a log scale, ggplot2 formats the breaks like 10^x. I'd like it to not do that. For example, the code below should display a graph with ticks at 1, 2, 5 etc, not 10^0, 10^0.3, 10^0.69 etc. library(ggplot2) dfr <- data.frame(x = 1:100, y = rlnorm(100)) breaks <- as.vector(c(1, 2, 5) %o% 10^(-1:1)) p1 <- ggplot(dfr, aes(x, y)) + geom_point() + scale_y_log10(breaks = breaks) print(p1) I guess that adding a formatter argument to scale_y_log10 would do the trick, but I'm not sure what to put in the argument, or where the options might be documented.

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• matlab noninteger step indexing

  - by rlbond

  So, I have a vector: k = 1:100; And I want to take 19 elements from it, which are roughly equally-spaced. So I write this: m = k(1:(99/18):end); This works great, except for a tiny problem: Warning: Integer operands are required for colon operator when used as index m = 1 7 12 18 23 29 34 40 45 51 56 62 67 73 78 84 89 95 100 Now, I understand why this comes up, but I'd like to get rid of that warning. Is there a "right" way to do this without a warning?

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• C dynamic memory allocation for table of structs

  - by JosiP

  Hi here is my code. I want to dynamincly change no of elemnts in table with structs __state: typedef struct __state{ long int timestamp; int val; int prev_value; }*state_p, state_t; int main(int argc, char **argv){ int zm; int previous_state = 0; int state = 0; int i = 0; int j; state_p st; //here i want to have 20 structs st. st = (state_p) malloc(sizeof(state_t) * 20); while(1){ previous_state = state; scanf("%d", &state); printf("%d, %d\n", state, previous_state); if (previous_state != state){ printf("state changed %d %d\n", previous_state, state); // here i got compile error: main.c: In function ‘main’: main.c:30: error: incompatible type for argument 1 of ‘save_state’ main.c:34: error: invalid type argument of ‘->’ main.c:34: error: invalid type argument of ‘->’ save_state(st[i],previous_state, state); } i++; } return 0; } I suppose i have to change that st[i] to smth like st+ptr ? where pointer is incermeting in each loop iteration ? Or am I wrong ? When i change code: initialization into state_p st[20] and in each loop iteration i put st[i] = (state_p)malloc(sizeof(state_t)) everything works fine, but i want to dynammicly change number of elemets in that table. Thx in advance for any help

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• Make Map Key Sorted According To Insert Sequence

  - by Yan Cheng CHEOK

  Without help from additional container (like vector), is it possible that I can make map's key sorted same sequence as insertion sequence? #include <map> #include <iostream> using namespace std; int main() { map<const char*, int> m; m["c"] = 2; m["b"] = 2; m["a"] = 2; m["d"] = 2; for (map<const char*, int>::iterator begin = m.begin(); begin != m.end(); begin++) { // How can I get the loop sequence same as my insert sequence. // c, b, a, d std::cout << begin->first << std::endl; } getchar(); }

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• The Cleanest Reset for ARM Processor

  - by waffleman

  Lately, I've been cleaning up some some C code that runs on an ARM7 controller. In some situations (upgrade, fatal error, etc...) the program will perform a reset. Presently it just jumps to 0 and assumes that the start-up code will reinitialize everything correctly. It got me to thinking about what would be the best procedure a la "Leave No Trace" for an ARM reset. Here is my first crack at it: void Reset(void) { /* Disable interrupts */ __disable_interrupts(); /* Reset peripherals, externals and processor */ AT91C_BASE_RSTC->RSTC_RCR = AT91C_RSTC_KEY | AT91C_RSTC_PERRST | AT91C_RSTC_EXTRST| AT91C_RSTC_PROCRST; while(AT91C_BASE_RSTC->RSTC_RSR & AT91C_RSTC_SRCMP); /* Jump to the reset vector */ (*(void(*)())0)(); } Anything I haven't considered?

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• Rotate a feature Image in Open Layers

  - by Ozaki

  I have an open layers map. It adds and removes my "imageFeature" every 10secs or so. I have a JSON feed that gives me the rotation that I need, I have a request to get that rotation and set it as a variable of rotationv. Everything works but the fact when the image is recreated it does not update the rotation. My code is as follows: JSON request: var rotationv = (function () { rotationv = null; $.ajax({ 'async': false, 'global': true, 'url': urldefault, 'dataType': "json", 'success': function (data) { rotationv = data.rotation; } }); return rotationv })(); Creating image feature: imageFeature = new OpenLayers.Feature.Vector( new OpenLayers.Geometry.Point(mylon, mylat), { rotation: rotationv } ); The image is set in the styling elsewhere. Why does this not rotate my image?

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• Online chart editor

  - by Alexander Gladysh

  I love to use Google Documents as MS Word and MS Excel replacements for online collaboration. However, now I need to discuss architecture layout for my software. Nothing too fancy, perhaps a little (pseudo-)UML, but mostly basic shapes (rectangles, ellipses etc.) with labels, connected by thin lines or arrows. In olden Windows times I'd go for Visio, and be happy. But now I want to use online tool. Preferably free. No need for code reverse engineering etc., just plain assisted vector drawing. Any advice? What do you use?

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• 3 hash functions to best hash sliding window strings for a bloom filter with minimum collisions

  - by Duaa

  Hi all: I need 3 hash functions to hash strings of a sliding window moving over a text, to be used later to search within a bloom vector. I'm using C# in my programming I read something about rolling hash functions and cyclic polynomials, they are used for sliding window applications. But really, I did not find any codes, they are just descriptions So please, if anyone have any idea about 3 best C# hash functions to use with sliding window strings of fixed size (5-char), that consume less time and have minimum number of collisions, either they are rolling hash functions or others, please help me with some C# codes or links to hash functions names Duaa

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• Crash generated during destruction of hash_map

  - by Alien01

  I am using hash_map in application as typedef hash_map<DWORD,CComPtr<IInterfaceXX>> MapDword2Interface; In main application I am using static instance of this map static MapDword2Interface m_mapDword2Interface; I have got one crash dump from one of the client machines which point to the crash in clearing this map I opened that crash dump and here is assembly during debugging > call std::list<std::pair<unsigned long const ,ATL::CComPtr<IInterfaceXX> >,std::allocator<std::pair<unsigned long const ,ATL::CComPtr<IInterfaceXX> > > >::clear > mov eax,dword ptr [CMainApp::m_mapDword2Interface+8 (49XXXXX)] Here is code where crash dump is pointing. Below code is from stl:list file void clear() { // erase all #if _HAS_ITERATOR_DEBUGGING this->_Orphan_ptr(*this, 0); #endif /* _HAS_ITERATOR_DEBUGGING */ _Nodeptr _Pnext; _Nodeptr _Pnode = _Nextnode(_Myhead); _Nextnode(_Myhead) = _Myhead; _Prevnode(_Myhead) = _Myhead; _Mysize = 0; for (; _Pnode != _Myhead; _Pnode = _Pnext) { // delete an element _Pnext = _Nextnode(_Pnode); this->_Alnod.destroy(_Pnode); this->_Alnod.deallocate(_Pnode, 1); } } Crash is pointing to the this->_Alnod.destroy(_Pnode); statement in above code. I am not able to guess it, what could be reason. Any ideas??? How can I make sure, even is there is something wrong with the map , it should not crash?

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• Mapping words to numbers with respect to definition

  - by thornate

  As part of a larger project, I need to read in text and represent each word as a number. For example, if the program reads in "Every good boy deserves fruit", then I would get a table that converts 'every' to '1742', 'good' to '977513', etc. Now, obviously I can just use a hashing algorithm to get these numbers. However, it would be more useful if words with similar meanings had numerical values close to each other, so that 'good' becomes '6827' and 'great' becomes '6835', etc. As another option, instead of a simple integer representing each number, it would be even better to have a vector made up of multiple numbers, eg (lexical_category, tense, classification, specific_word) where lexical_category is noun/verb/adjective/etc, tense is future/past/present, classification defines a wide set of general topics and specific_word is much the same as described in the previous paragraph. Does any such an algorithm exist? If not, can you give me any tips on how to get started on developing one myself? I code in C++.

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• Why does MySQL autoincrement increase on failed inserts?

  - by Sorcy

  A co-worker just made me aware of a very strange MySQL behavior. Assuming you have a table with an auto_increment field and another field that is set to unique (e.g. a username-field). When trying to insert a row with a username thats already in the table the insert fails, as expected. Yet the auto_increment value is increased as can be seen when you insert a valid new entry after several failed attempts. For example, when our last entry looks like this... ID: 10 Username: myname ...and we try five new entries with the same username value on our next insert we will have created a new row like so: ID: 16 Username: mynewname While this is not a big problem in itself it seems like a very silly attack vector to kill a table by flooding it with failed insert requests, as the MySQL Reference Manual states: "The behavior of the auto-increment mechanism is not defined if [...] the value becomes bigger than the maximum integer that can be stored in the specified integer type." Is this expected behavior?

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• how to substract numbers from levels

  - by romunov

  Dear SOFers, I would like to cut a vector of values ranging 0-70 to x number of categories, and would like the upper limit of each category. So far, I have tried this using cut() and am trying to extract the limits from levels. I have a list of levels, from which I would like to extract the second number from each level. How can I extract the values between space and ] (which is the number I'm interested in)? I have: > levels(bins) [1] "(-0.07,6.94]" "(6.94,14]" "(14,21]" "(21,28]" "(28,35]" [6] "(35,42]" "(42,49]" "(49,56]" "(56,63.1]" "(63.1,70.1]" and would like to get: [1] 6.94 14 21 28 35 42 49 56 63.1 70.1 Or is there a better way of calculating the upper bounds of categories?

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• c++ library for endian-aware reading of raw file stream metadata?

  - by Kache4

  I've got raw data streams from image files, like: vector<char> rawData(fileSize); ifstream inFile("image.jpg"); inFile.read(&rawData[0]); I want to parse the headers of different image formats for height and width. Is there a portable library that can can read ints, longs, shorts, etc. from the buffer/stream, converting for endianess as specified? I'd like to be able to do something like: short x = rawData.readLeShort(offset); or long y = rawData.readBeLong(offset) An even better option would be a lightweight & portable image metadata library (without the extra weight of an image manipulation library) that can work on raw image data. I've found that Exif libraries out there don't support png and gif.

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• code throws std::bad_alloc, not enough memory or can it be a bug?

  - by Andreas

  I am parsing using a pretty large grammar (1.1 GB, it's data-oriented parsing). The parser I use (bitpar) is said to be optimized for highly ambiguous grammars. I'm getting this error: 1terminate called after throwing an instance of 'std::bad_alloc' what(): St9bad_alloc dotest.sh: line 11: 16686 Aborted bitpar -p -b 1 -s top -u unknownwordsm -w pos.dfsa /tmp/gsyntax.pcfg /tmp/gsyntax.lex arbobanko.test arbobanko.results Is there hope? Does it mean that it has ran out of memory? It uses about 15 GB before it crashes. The machine I'm using has 32 GB of RAM, plus swap as well. It crashes before outputting a single parse tree. The parser is an efficient CYK chart parser using bit vector representations; I presume it is already near the limit of memory efficiency. If it really requires too much memory I could sample from the grammar rules, but this will decrease parse accuracy of course.

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• How to get orientation of android from gyrsocope sensor events ?

  - by Pritam

  I am using android 2.3 on Nexus S and want to get orientation from gyroscope sensor events. As gyro gives angular velocity how to use this for getting device orientation ? Also is there any way we can get pure linear accelerations on phone's axis, without gravity vector. I expected this from Linear acceleration sensor event but just found a post and referred android source as well for Sensor which currently uses only accelerometer. So what's the best way to combine the readings from both hardware to get pure accelerations without gravity inclusions ? Thanks.

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• E4X in ActionScript

  - by Brian Genisio

  Hey all, Looking at the E4X implementation in ActionScript, it occurs to me that they had to figure out how to do three things that I am not sure can be done within ActionScript regularly: Properties/Getters prefixed with @: var myAttribute = xmlPerson.@name; Nameless functions for filtering: xmlData.person.(/* predicate */) lambda syntax for predicates: xmlData.person.(@name == "Brian") So here is my question: Are these just one-off capabilities (much like Vector.<>) they put in just for E4X, therefore keeping out of reach for us? Or do we, as ActionScript developers, have access to these features? More specifically, I'd love to get access to the expression tree of that lambda predicate for my own code (not tied to the XML classes in any way). I figured out that this is called the "filter operator"... but I am not sure how to harness it. Not sure I can... since ActionScript does not allow for operator overloading :(

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• Is it safe to use the same parameters for input and output in D3DX functions?

  - by JB

  Using the D3DX library that is a part of directX, specifically directx9 in this case, I'm wondering if it's safe to use the same matrix (or vector etc) for input and ouput D3DXMATRIX mat; D3DXMatrixInverse(&mat, NULL, &mat); I've been avoiding doing so, assuming that it would result in bad things happening when parts of the array got partly overwritten as results are calculated but I see an awful lot of code around that does exactly this. A brief test indicates that it seems to work ok, so I'm assuming that the D3DX functions take a copy where necessary of the input data, or some other method to ensure that this works ok, but I can't find it documented anywhere so I'm reluctant to rely on it working. Is there any official statement on using the functions like this?

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• log4j: Change format of loggers configured in another library.

  - by Ignacio Thayer

  Using clojure, I've been able to successfully setup log4j very simply by using this log4j.properties file, and including log4j in my classpath. # BEGIN log4j.properties log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout log4j.appender.STDOUT.layout.ConversionPattern=%d{MMdd HHmmss SSS} %5p %c [%t] %m\n log4j.rootLogger=DEBUG, STDOUT Then after :use'ing clojure.contrib.logging, I'm able to print a statement with the desired formatting as expected like so: (info "About to print this") (debug "This is debug-level") My question is how to achieve a consistent formatting for logging statements made from loggers configured in other libraries. I thought I could find existing loggers using org.apache.log4j.LogManager.getCurrentLoggers() and change the PatternLayouts there, but I'm not able to iterate over that enumeration in clojure, as I get the following error: Dont know how to create ISeq from: java.util.Vector$1 I assume this is possible somehow, and probably very simply. How? Thanks much.

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• Which machine learning library to use

  - by Space_C0wb0y

  I am looking for a library that, ideally, has the following features: implements hierarchical clustering of multidimensional data (ideally on similiarity or distance matrix) implements support vector machines is in C++ is somewhat documented (this one seems to be hardest) I would like this to be in C++, as I am most comfortable with that language, but I will also use any other language if the library is worth it. I have googled and found some, but I do not really have the time to try them all out, so I want hear what other people had for experiences. Please only answer if you have some experience with the library you recommend. P.S.: I could also use different libraries for the clustering and the SVM.

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