type conversion performance optimizable?
c#,xml,csv,optimization,type-conversion
IEnumerable<string> values = new List<string>(); values = … Probably not going to be a big deal, but why create a new List<string>() just to throw it away. Replace this with either: IEnumerable<string> values; values = … If you need values defined in a previous scope, or else just: Enumerable<string> values...
Does compiler optimize operation on const variable and literal const number?
You have some good answers already that answer your factual question: No, the C# compiler does not generate the code to do a single multiplication by 86. It generates a multiplication by 43 and a multiplication by 2. There are some subtleties here that no one has gone into though....
Optimization - is union the best way to go in this case?
sql-server,join,optimization,union
Well first of all, you can use UNION ALL, which will leave out the duplication check. This will be much faster. Another suggestion is the IN() in your first SELECT. This could cause long runtimes if your subquery returns many rows. I would suggest to redesign it from this: select...
Minimum difference between sum of two numbers in an array
c++,algorithm,optimization,dynamic-programming
First of all, you are right that iteratively combining the best remaining student with the worst remaining student gives you the optimum result (see proof below). However, you don't calculate the cost of that solution correctly. You have to run through all pairs of your combination in order to find...
When compiled with -O2, program skips assignment
while((j < nprimos) && (num % primos[j] > 0)) ++j; One way for this while loop to terminate is when j == nprimos (when i == 0 and therefore num == 1, for instance; obviously 1 isn't divisible by any prime number.) In this case the access to primos[j] in...
Which way of setting fields value is better and why?
Way 2 is better because it gives you a unified way of setting a variable value. But it brings in a risk, because you're calling an overrideable method in a constructor. So the right syntax is using the final keyword: public final void setField(int field){ this.field = field; } //way...
SAS drop multiple variables indexed by tens
If the var<xx> variables are all multiples of ten, i.e. there are no other variables beginning with var, you can use the colon-operator, which acts as a wildcard, e.g. drop var: ; /* drop all variables beginning with 'var' */ Alternatively, you can dynamically generate a list of all the...
Perform integer division using multiplication
assembly,optimization,bit-manipulation,division,multiplication
That method is called, "Division by Invariant Multiplication". The constants that you're seeing are actually approximates of the reciprocal. So rather than computing: N / D = Q you do something like this instead: N * (1/D) = Q where 1/D is a reciprocal that can be precomputed. Fundamentally, reciprocals...
Prefetching double class member requires casting to char*?
c++,performance,optimization,x86,prefetch
If you read the description for _mm_prefetch() from the site you linked to it has : void _mm_prefetch (char const* p, int i) Fetch the line of data from memory that contains address p to a location in the cache heirarchy specified by the locality hint i. So you need...
Optimal Compare Algorithm for finding string matches in List of strings C#
c#,string,algorithm,optimization,language-agnostic
I decided to add this answer not because it is the optimal solution to your problem, but to illustrate two possible solutions that are relatively simple and that are somewhat in line with the approach you seem to be following yourself. The (non-optimized) sample below provides an extremely simple prefix...
What is the advantage of the paperboat format in performance optimization of ML?
optimization,machine-learning,dataset
I don't know if this format really provides better representation, but I can speculate why it can be more efficient. First, as they state at format description, "Having data of the same precision consecutive enables hardware vectorization."; consider also wikipedia: "Vector processing techniques have since been added to almost all...
OpenCV FAST corner detection SSE implementation walkthrough
c,performance,opencv,optimization,sse
As harold said, delta is used to make unsigned comparsion. Let's describe this implementation by steps: __m128i x0 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[0])), delta); __m128i x1 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[4])), delta); __m128i x2 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[8])), delta); __m128i x3 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[12])), delta); m0 =...
CSSRules group selectors with common properties
javascript,jquery,html,css,optimization
This looks great, and I have only a minor suggestion. Change your code as follows: for (j = 0; rule = rules[j]; j++) { var styles = rule.style, style, k; var elements = document.querySelectorAll(rule.selectorText); if(elements.length) { for(k = 0; style = styles[k]; k++) { ... } console.log(rule.cssText); } } This...
weird optimization (remove a function) in GCC
This code causes undefined behaviour: uint32_t *p = (uint32_t *)vector; uint32_t tmp = p[0]; The memory pointed to by vector is an object of type uint64_t , however you read it via an lvalue of type uint32_t. This violates the strict aliasing rule. Since your program always calls this function,...
Performing large queries on Array or DB in php? [closed]
php,mysql,arrays,performance,optimization
Database connections are going to be the most expensive part of the algorithm, so minimize the amount of time each connection will last. Pull it from the database and loop through the array. Unless you are doing a function that would be very quick in a database (ie- sorting on...
JQuery Show Hide Multiple Div Button
javascript,jquery,performance,function,optimization
Using your HTML with only two buttons and identical CSS The following JS works for better for me: Javascript: var newsDepth = 3; var maxNewsDepth = 3; $('#show-more-news').hide(); $('#show-more-news').click( function () { (newsDepth < maxNewsDepth ) && newsDepth++; $('#art-' + newsDepth).show(); $('#show-less-news').show(); if (newsDepth == maxNewsDepth) $('#show-more-news').hide(); }); $('#show-less-news').click( function...
Speeding up a function involving mapply and integrate
r,optimization,integrate,mapply
You are performing a large number of independent integrations. You can speed things up by performing these integrations on separate cores simultaneously (if you have a multicore processor available). The problem is that R performs its calculations in a single threaded manner by default. However, there are a number packages...
One-dimensional binpacking algorithm with relative costs
algorithm,optimization,bin-packing
If the problem under consideration is the generalized assignment problem, it is NP-hard but admits an approximation algorithm. From a brief look, the approximation ratio depends on the approximation ratio of an approximation algorithm for the knapsack problem, which in turn admits a fully polynomial time approximation scheme. In total....
Optimizing for Social Leaderboards
python,google-app-engine,optimization,twitter,leaderboard
I would organize the task like this: Make an asynchronous fetch call to the Twitter feed Use memcache to hold all the AuthAccount->User data: Request the data from memcache, if it doesn't exist then make a fetch_async() call to the AuthAccount to populate memcache and a local dict Run each...
How to efficiently select neighbour in 1-dimensional and n-dimensional space for Simulated Annealing
java,algorithm,search,optimization,simulated-annealing
So you are trying to find an n-dimensional point P' that is "randomly" near another n-dimensional point P; for example, at distance T. (Since this is simulated annealing, I assume that you will be decrementing T once in a while). This could work: double[] displacement(double t, int dimension, Random r)...
Does LINQ make use of underlying data structure?
They do where it makes sense, typically not for the actual type but for an interface (for example they check for IList when it helps speedup)
Optimizing a simple linear curve (constant and coefficient estimated from a regression)
If the functions are linear, then they will be at a minimum at the lower end of the range where beta>=0, and at the upper end of the range if beta<=0 - no need to use optimize(). It's not entirely clear what you're expecting the code to do - if...
Hashmap with time values, want to find value at specific second
You don't need a (Linked)HashMap for this job. Use a NavigableMap (TreeMap would be the standard implementation) that provides a lot of useful operations for such use-cases: floor/ceiling, higher/lower, first/last and so on. // get the value at this specific time or the last one before that Double valueAtTheTime =...
Picking Ad Mob Mediation Networks 2015
MillenialMedia - Pretty decent engineering. Pretty good revenue Inmobi - Good revenue. Sometimes really dodgy ads. I've experiemented with half a dozen others, but they provided insignificant revenue, or provided many bugs. But your mileage may vary....
Disable JRockit Optimzation per class
optimization,jvm-hotspot,jrockit
You can create an opt file, see JRockit R28: http://docs.oracle.com/cd/E15289_01/doc.40/e15059/crash.htm#BABJGICB Earlier releases: https://docs.oracle.com/cd/E13150_01/jrockit_jvm/jrockit/geninfo/diagnos/crash.html#wp1010461...
How can I optimize filename generator with underscore?
Note that there are 2n-1 different such names for a string of lengh n, as there can or can not be a _ between any two characters. For your long-long name that makes 134,217,728 variants! Regardless of what algorithm you use, this will take a very long time. One way...
How minimal can an SVG be?
Removing the viewBox creates a significant semantic difference as the SVG will no longer scale (i.e. be responsive to UA resizes). This only applies if you're viewing the image directly though if you're viewing it as a background-image or via a SVG <image> tag or html <img> tag then the...
Inline function at -O0 causes link failure in clang [duplicate]
c,optimization,clang,inline,c99
At -O1 and greater it is not calling the function it just moves the code into main, we can see this by using godbolt which shows the asm as follows see it live: main: # @main pushq %rax movl $.L.str, %edi movl $42, %esi xorl %eax, %eax callq printf xorl...
use empty() or just use > in php which is the fastest way
You can try that out yourself using php's microtime function: $saleprice = 1; $start = microtime(true); if(!empty($saleprice)) echo $saleprice . '<br/>'; echo 'empty: ' . number_format(( microtime(true) - $start), 30) . '<br/>'; $start = microtime(true); if(!is_null($saleprice)) echo $saleprice . '<br/>'; echo 'is_null: ' . number_format(( microtime(true) - $start), 30) ....
Efficiently transferring elements between arrays
javascript,arrays,optimization,memory-management,data-structures
splice is pretty harmful for performance in a loop. But you don't seem to need mutations on the input arrays anyway - you are creating new ones and overwrite the previous values. Just do function doTransfers() { var A_pending = []; var B2_pending = []; for (var i = 0;...
Is there a more efficient way to solve this?
python,python-2.7,optimization,matrix
In terms of refactoring, you almost certainly want to avoid "brute force" in the sense of having to explicitly type out all your cases :) @alexmcf addresses this above. In conceptual terms, your approach follows the problem statement directly: check all neighbors for each number in the matrix and sum...
In general, how expensive is calling an external program?
Like I said in my comment above, perhaps it would be best if you simply tried it and did some benchmarking. I'd expect this to depend primarily on the OS you're using. That being said, starting a new process generally is many orders of magnitude slower than calling a subroutine...
efficient way of passing Data between Matlab functions
matlab,function,optimization,parameter-passing
As far as I know, matlab does not actually copy the content of the data you pass to a function until the point when you modify it in the function itself - in which case it makes a local copy and that takes some CPU time. Therefore, as long as...
Mysql optimize to avoid table scan
mysql,sql,table,optimization,scan
You could try a self join like this: SELECT COUNT(DISTINCT sw1.word_id) FROM sentence_word sw1 JOIN sentence_word sw2 ON ( sw1.sent_id = sw2.sent_id AND sw2.word_id = [your word id] ) WHERE sw1.word_id != [your word id] or perhaps even better SELECT COUNT(DISTINCT sw1.word_id) FROM sentence_word sw1 JOIN sentence_word sw2 ON (...
Absolute value equality of variables in MATLAB optimization
It is not a convex problem, hence it cannot be solved directly with the tools you mention. It is inherently combinatorial, in the sense that you can enumerate cases based on the sign of the two variables, and for every such case, a linear equality holds. Hence, you can either...
Brent's method in the R optim implementation always returns the same local minimum
Your function is NOT convex, therefore you will have multiple local/global minima or maxima. For your function I would run a non traditional/ derivative free global optimizer like simulated annealing or genetic algorithm and use the output as a starting point for BFGS or any other local optimizers to get...
How to improve performance method GetThumbnailAsync in window phone 8.1
c#,image-processing,optimization,winrt-xaml
You are currently awaiting file.GetThumbnailAsync for each file which means that although the function is executed asynchronously for each file, it is executed in order, not in parallel. Try converting each async operation returned from file.GetThumbnailAsyncto a Task and then storing those in a list and then await all tasks...
Optimizing a large if-else branch with binary search
c,optimization,binary-search,linear-search
You should look at the generated instructions to see (gcc -S source.c), but generally it comes down to these three: 1) N is too small. If you only have a 8 different branches, you execute an average of 4 checks (assuming equally probable cases, otherwise it could be even faster)....
Optimizing a sub-sub-query in MySQL
If you want only the most recent comment for a given user, then you can express this as: SELECT rc.* FROM requests r JOIN requests_comments rc ON rc.request_id = r.id WHERE r.username = 'someuser' ORDER BY rc.commented_at DEC LIMIT 1; For performance, you want an index on requests(username, id) and...
Getting the maximum sum of pairs' second elements given weight limitation on the first elements
java,algorithm,sorting,optimization
This is an instance of the Knapsack Problem. The Wikipedia page lists a lot of known algorithm that solve this efficiently. You might want to gather some inspiration from these algorithms.
Optimizing Ansible Transport\SSH for Unconventional Networks
networking,optimization,ssh,ansible
If you are working in a network where the connection might be lost 'during' execution of a play/task then I'm not sure if (read: I don't think) ansible saves the context of execution so often as to recover from such issues. If your network is bad, you should fix that....
nuZ: Use of soft-assertions with weights and ids
By default Z3 solves the objectives one at a time and finds the lexicographically best solution. First it tries to satisfy as many soft constraints from "first". The weight you associate with the soft constraints is a penalty for not satisfying the constraint. That is, it is not an award,...
Disabling fp-model strict when using ifort with f2py
python,numpy,optimization,fortran,f2py
The flags -xhost -openmp -fp-model strict come from def get_flags_opt(self): return ['-xhost -openmp -fp-model strict'] in the file site-packages/numpy/distutils/fcompiler/intel.py for the classes that invoke ifort. You have two options to modify the behavior of these flags: call f2py with the --noopt flag to suppress these flags call f2py with the...
nuZ: What does the model say
There isn't much more to it. For soft constraints the number on the right of "|->" is given as follows. Suppose we assert (assert-soft F1 :weight w1 :id first) (assert-soft F2 :weight w2 :id first) (assert-soft F3 :weight w3 :id first) And suppose M is a model maximal assignment that...
FastDOM - Read / write every 17ms?
javascript,dom,optimization,asynchronous,requestanimationframe
Both types of DOM operations (read/write) have their own job queues. Each queue is flushed (e.g. all jobs in it are ran/executed) every requestAnimationFrame If you add 100 read operations all within 5ms, for example, (during a loop for instance), all of those read operations will (most likely) occur the...
glclearcolor best color?
No (technically there could be a difference, since OpenGL does not impose any performance requirements on the functioncall). Btw. you should set the clear color before calling clear....
Java: Assigning a variable its current value?
java,variables,optimization,value
the cost of calling the method isEmpty() (allocating new space in the thread stack etc) negate any gains. if you want to assign an empty String to the variable, its most efiicient to do so without the if statement.
How configure Stanford QNMinimizer to get similar results as scipy.optimize.minimize L-BFGS-B
java,optimization,machine-learning,scipy,stanford-nlp
What you have should be just fine. (Have you actually had any problems with it?) Setting termination both on max iterations and max function evaluations is probably overkill, so you might omit the last argument to qn.minimize(), but it seems from the documentation that scipy does use both with a...
C++ Optimization breaking OLE Automation program (non-MFC)
c++,optimization,visual-studio-2013,ole,office-automation
In this code: if (cmd==DISPATCH_PROPERTYPUT) { DISPID dispidNamed=DISPID_PROPERTYPUT; /* <--- PROBLEM LINE here */ dispParams.cNamedArgs=1; dispParams.rgdispidNamedArgs=&dispidNamed; } dispidNamed is a local variable to the code block it is in (i.e. the area delimited by { }). After the } is reached it ceases to exist. Then rgdispidNamedArgs is a dangling...
R: NaNs produced in Log-Likelihood optimisation
Optim converges with your initial parameters, so I'm not sure there is a problem. But, you can also try using the alternative optimization routines and run a simple test to see what parameters are giving warnings ## Test results with other methods x1 <- optim(c(17,5,3,4,27,13),LL,method="BFGS",u=u) ps <- x1$par x2 <-...
How to interpret the output of the CPLEX interactive optimizer?
The % gap is the relative difference between the best solution and the best known bound for a solution. This is guaranteed to be higher than the gap between the best known solution and the true global optimum. In your case, the best bound is 83.9275, the best bound is...
Ackley optimization Matlab
Since you mentioned "evolution strategy" in your comment to @Divkar, I am assuming you want to optmize the ackley function using any evolutionary algorithm. In fact, if this is the case and if you are familiar with the Particle Swarm Optimization (PSO) , there is a submission (among many) in...
Placing Limits on Optim
r,optimization,regression,rscript
This seems to work fine: opt1 <- optim(startparam, fn=ls,method="L-BFGS-B", Val=Val,Hi=Hi,Di=Di, lower =c(20,10,0), upper =c(100,70,25)) note that the values of Val, Hi, Di get passed through optim to the objective function....
Add a python flag cx_freeze to executable
python,optimization,distribution,cx-freeze,pyglet
You can use the same -O flag when you run cx_freeze to generate your final build, meaning that the cx_freeze generated bytecode will already be optimized. From the cxfreeze docs: cxfreeze hello.py --target-dir dist Further customization can be done using the following options: ... -O optimize generated bytecode as per...
Alpha blending using table lookup is not as fast as expected
c,performance,optimization,alphablending,lookup-tables
Table lookup is not a panacea. It helps when the table is small enough, but in your case the table is very big. You write 16 megabytes used for the table is not an issue in this case which I think is very wrong, and is possibly the source of...
Vary coefficient in system of equation in Matlab's fsolve
You can do it in one line using arrayfun, though it looks kind of convoluted and simply looping over p might be faster: function F = myfun(x,p) F = [p*x(1) - x(2) - exp(-x(1)); -x(1) + 2*x(2) - exp(-x(2))]; p_values = -3:.1:3; x = arrayfun(@(p)fsolve(@(x)myfun(x,p), x0), p_values, 'UniformOutput', false) and...
Loop unrolling in inlined functions in C
Well, obviously the compiler isn't 'smart' enough to propagate the n constant and unroll the for loop. Actually it plays it safe since arg->n can change between instantiation and usage. In order to have consistent performance across compiler generations and squeeze the maximum out of your code, do the unrolling...
Better to declare JavaScript Object inside for loop or outside in terms of time optimization
javascript,arrays,optimization,variable-declaration
Both are the same. for loops don't create a new scope so the variables are hoisted to the top of the containing function scope. ex: > i undefined > for (var i = 0; i < 5; i++) { var test = i; } undefined > i 5 > test...
Algorithms for minimizing single-variable functions
algorithm,optimization,numerical-methods
For this setting, I'd go with Golden Section Search. Convexity implies unimodality, which is needed by this method. Conversely, this method does not need derivatives. You can find derivatives numerically, but that's another way of saying "multiple function assessments"; might as well use these for golden-section partitions. ...
Minimize a function with two variables
There are a few problems with your overall process that cause trouble. First of all as @user227710 mentions in the comments you should replace && with &. These have different meanings. Now for the optimiser It looks like you want to set limits to your parameters (i.e. what is known...
Slow start-up of large programs
It turns out the delay is the Microsoft antivirus program scanning the executable each time it's run. Disabling protection on that file cuts the time to 47 milliseconds.
Why do we need to put the *.odex files under /system/app even if we already have /data/dalvik-cache?
android,optimization,virtual-machine,loader,dalvik
The /system/app directory is read-only on normal (non-developer) devices, and only updated when the system receives an update. The point of /system/app/*.odex is that the .odex file can be delivered as part of a system update, so it doesn't have to be generated on the first post-update boot, and doesn't...
Better way to check if subdomain exists without using database query or hosts file
php,apache,symfony2,optimization,wildcard-subdomain
You could cache all each of the subdomain requests (using something like Doctrine cache as a wrapper for whatever caching system you use) so that each subsequent check would only need to check the cache rather than the database. Also when adding/removing/updating your subdomain object you could update the cache...
Optimization Toolbox (fmincon) - How to set logical constraints?
What you are looking for are nonlinear constraints, fmincon can handle it (I only know the command, not the GUI) with the argument nonlcon. For more information look at this guide http://de.mathworks.com/help/optim/ug/fmincon.html How would you implement this? First create a function function [c, ceq] = mycondition(x) c = -max(x)/min(x)/10; ceq...
How to make faster queries on my mysql table?
mysql,optimization,query-optimization
It is not possible to optimize a mixture of ASC and DESC, as in ORDER BY t.fecha DESC, t.idsensor ASC You tried a covering index: INDEX `sensor_temp` (`idsensor`,`fecha`,`temperatura`) However, this covering index may be better: INDEX `sensor_temp` (`fecha`,`idsensor`,`temperatura`) Then, if you are willing to get the sensors in a different...
Dynamic programming: how to design algorithm for when there are two factors to consider?
algorithm,optimization,dynamic-programming,frequency
There is no need for Dynamic Programming for this problem. It is a simple sorting problem, with a slight twist. Find frequency / length for each file. This gets you, how frequent is each unit length access for the file. Sort these in descending order since each file is "penalized"...
Matlab @fminunc objective function optimization
matlab,function,optimization,maximize
Both your functions return a vector of values whereas fminunc requires that the function returns a scalar / single value. The error is pretty clear. The function fminunc is trying to find the best solution that minimizes a cost function, so what you need to supply is a cost function....