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  • Can bad stuff happen when dividing 1/a very small float?

    - by Jeremybub
    If I want to check that positive float A is less than the inverse square of another positive float B (in C99), could something go wrong if B is very small? I could imagine checking it like if(A<1/(B*B)) but if B is small enough, would this possibly result in infinity? If that were to happen, would the code still work correctly in all situations? in a similar vein, I might do if(1/A>B*B) Which might be slightly better because B*B might be zero if B is small (is this true?) Finally, a solution that I can't imagine being wrong is if(sqrt(1/A)>B) Which I don't think would ever result in zero division, but still might be problematic if A is close to zero. So basically, my questions are Can 1/X ever be infinity if X is greater than zero (but small)? Can X*X ever be zero if X is greater than zero? Will comparisons with infinity work the way I would expect them to?

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  • Collision point of 2 curves in a 3d-room

    - by Frank
    Hello, i am programming a small game for quite some time. We started coding a small FPS-Shooter inside of a project at school to get a bit experience using directX. I dont know why, but i couldnt stop the project and started programming at home aswell. At the moment i am trying to create some small AI. Of cause thats definatlly not easy, but thats my personal goal anyways. The topic could prolly fill multiple books hehe. I've got the walking part of my bots done so far. They walk along a scriped path. I am not working on the "aiming" of the bots. While programming that i hit on some math problem i couldnt solve yet. I hope of your input on this to help me get further. Concepts, ideas and everything else are highly appreciated. Problem: Calculate the position (D3DXVECTOR3) where the curve of the projectile (depends on gravity, speed), hit the curved of the enemys walking path (depends on speed). We assume that the enemy walks in a constant line. Known variables: float projectilSpeed = 2000 m/s //speed of the projectile per second float gravitation = 9.81 m/s^2 //of cause the gravity lol D3DXVECTOR3 targetPosition //position of the target stored in a vector (x,y,z) D3DXVECTOR3 projectilePosition //position of the projectile D3DXVECTOR3 targetSpeed //stores the change of the targets position in the last second Variabledefinition ProjectilePosition at time of collision = ProjectilePos_t TargetPosition at time of collision = TargetPos_t ProjectilePosition at time 0, now = ProjectilePos_0 TargetPosition at time 0, now = TargetPos_0 Time to impact = t Aim-angle = theta My try: Found a formular to calculate "drop" (Drop of the projectile based on the gravity) on Wikipedia: float drop = 0.5f * gravity * t * t The speed of the projectile has a horizontal and a vertical part.. Found a formular for that on wikipedia aswell: ProjectilVelocity.x = projectilSpeed * cos(theta) ProjectilVelocity.y = projectilSpeed * sin(theta) So i would assume this is true for the projectile curve: ProjectilePos_t.x = ProjectilePos_0.x + ProjectileSpeed * t ProjectilePos_t.y = ProjectilePos_0.y + ProjectileSpeed * t + 0.5f * gravity * t * t ProjectilePos_t.z = ProjectilePos_0.z + ProjectileSpeed * t The target walk with a constant speed, so we can determine his curve by this: TargetPos_t = TargetPos_0 + TargetSpeed * D3DXVECTOR3(t, t, t) Now i dont know how to continue. I have to solve it somehow to get a hold on the time to impact somehow. As a basic formular i could use: float time = distanz / projectileSpeed But that wouldnt be truly correct as it would assume a linear "Trajectory". We just find this behaivor when using a rocket. I hope i was able to explain the problem as much as possible. If there are questions left, feel free to ask me! Greets from germany, Frank

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  • Dynamically created image doesn't show when <img>'s src is refreshed to point to it

    - by Obay
    Hello, I have a javascript function generateGraph() { ... jQuery.get('chart.php?month='+month+'&year='+year); document.getElementById('graph').src = 'charts/'+month+'_'+year+'.png'; ... } which is called onChange. It basically creates, if not exists, or refreshes if already exists, a PNG image (using the first line above) and supposedly displays the generated image (using the second line above). The first line works, but the second one doesn't. Meaning, the image is generated, but the second line can't display the image, unless the page is reloaded, or if the image being referred to already existed before the page was loaded (meaning the 1st line just "refreshed" the image) Any ideas as to why this is and how to fix it? Thanks much for your help in advance!

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  • calculating a gps coordinate given a point, bearing and distance

    - by user530509
    Hello, I have a problem which draws my back in some project for some time now. Im basically looking to trap a polygon using x,y points drawn by some script ive written. lat1,lon1 are the center gps cords of the polygon and im looking for its surrounding polygon. here is a part of my code in python: def getcords(lat1,lon1,dr,bearing): lat2=asin(sin(lat1)*cos(dr)+cos(lat1)*sin(dr)*cos(bearing)) lon2=lon1+atan2(sin(bearing)*sin(dr)*cos(lat1),cos(dr)-sin(lat1)*sin(lat2)) return [lat2,lon2] my input goes like this: lat1,lon1 - are given in decimal degrees. -dr is the angular computed by dividing the distance in miles by the earth's -raiuds(=3958.82) -bearing between 0-360 degrees. however for the input getcorsds1(42.189275,-76.85823,0.5/3958.82,30) i get [-1.3485899508698462, -76.8576637627568], however [42.2516666666667,-76.8097222222222] is the right answer. as for the angular distance i calculate it simply by dividing the distance in miles by the earth's raiuds(=3958.82). anybody?

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  • How to not use JavaScript with in the elements events attributes but still load via AJAX

    - by thecoshman
    I am currently loading HTMl content via AJAX. I have code for things on different elements onclick attributes (and other event attributes). It does work, but I am starting to find that the code is getting rather large, and hard to read. I have also read that it is considered bad practice to have the event code 'inline' like this and that I should really do by element.onclick = foobar and have foobar defined somewhere else. I understand how with a static page it is fairly easy to do this, just have a script tag at the bottom of the page and once the page is loaded have it executed. This can then attach any and all events as you need them. But how can I get this sort of affect when loading content via AJAX. There is also the slight case that the content loaded can very depending on what is in the database, some times certain sections of HTML, such as tables of results, will not even be displayed there will be something else entirely. I can post some samples of code if any body needs them, but I have no idea what sort of things would help people with this one. I will point out, that I am using Jquery already so if it has some helpful little functions that would be rather sweet¬

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  • How do calculators work with precision?

    - by zoul
    Hello! I wonder how calculators work with precision. For example the value of sin(M_PI) is not exactly zero when computed in double precision: #include <math.h> #include <stdio.h> int main() { double x = sin(M_PI); printf("%.20f\n", x); // 0.00000000000000012246 return 0; } Now I would certainly want to print zero when user enters sin(p). I can easily round somewhere on 1e–15 to make this particular case work, but that’s a hack, not a solution. When I start to round like this and the user enters something like 1e–20, they get a zero back (because of the rounding). The same thing happens when the user enters 1/10 and hits the = key repeatedly — when he reaches the rounding treshold, he gets zero. And yet some calculators return plain zero for sin(p) and at the same time they can work with expressions such as (1e–20)/10 comfortably. Where’s the trick?

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  • CSS3 new features...whats the point?

    - by benhowdle89
    I've been reading a lot of ways recently of how to avoid having to use Photoshop for things like gradients and shadows on buttons, when you can use CSS3 Box Shadow for such features. Now this is great, but obviously legacy browsers and most IE browsers don't yet implement CSS3 features, so my question is, why save yourself extra work in Photoshop when you can use CSS3 but then HAVE to use Photoshop for other browsers to see the desired effects? Isn't that just extra work?

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  • MSBuild / PowerShell: Copy SQL Server 2012 database to SQL Azure via BACPAC (for Continuous Integration)

    - by giveme5minutes
    I'm creating a continuous integration MSBuild script which copies a database in on-premise SQL Server 2012 to SQL Azure. Easy right? Methods After a fair bit of research I've come across the following methods: Use PowerShell to access the DAC library directly, then use the MSBuild PowerShell extension to wrap the script. This would require installing PowerShell 3 and working out how to make the MSBuild PowerShell extension work with it, as apparently MS moved the DAC API to a different namespace in the latest version of the library. PowerShell would give direct access to the API, but may require quite a bit of boilerplate. Use the sample DAC Framework Client Side Tools, which requires compiling them myself, as the downloads available from Codeplex only include the Hosted version. It would also require fixing them to use DAC 3.0 classes as they appear to currently use an earlier version of DAC. I could then call these tools from an <Exec Command="" /> in the MSBuild script. Less boilerplate and if I hit any bumps in the road I can just make changes to the source. Processes Using whichever method, the process could be either: Export from on-premise SQL Server 2012 to local BACPAC Upload BACPAC to blog storage Import BACPAC to SQL Azure via Hosted DAC Or: Export from on-premise SQL Server 2012 to local BACPAC Import BACPAC to SQL Azure via Client DAC Question All of the above seems to be quite a lot of effort for something that seems to be a standard feature... so before I start reinventing the wheel and documenting the results for all to see, is there something really obvious that I've missed here? Is there pre-written script that MS has released that I have not yet uncovered? There's an command in the GUI of SQL Server Management Studio 2012 that does EXACTLY what I'm trying to do (right click on local database, click "Tasks", click "Deploy Database to SQL Azure"). Surely if it's a few clicks in the GUI it must be a single command on the command line somewhere??

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  • Why might different computers calculate different arithmetic results in VB.NET?

    - by Eyal
    I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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  • Sms via a nokia phone over a serial port

    - by abigblackman
    Hi, I'm trying to send a sms via a Nokia phone over serial which is easy enough via putty. The commands from the nokia documentation works fine. However, trying to send the same commands from a c# application fails miserably. I've run Sysinternals PortMon and can see the commands come through OK, the only difference I can see is in the way it connects but I am having trouble finding the commands that would iron out those differences. The code I'm running looks a little bit like this using (SerialPort port = new SerialPort(comPort, 9600, Parity.None, 8, StopBits.One)) { port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived); port.ErrorReceived += new SerialErrorReceivedEventHandler(port_ErrorReceived); //port.ReceivedBytesThreshold = 1; port.DtrEnable = true; port.RtsEnable = true; port.ReadTimeout = 1; port.Handshake = Handshake.XOnXOff; try { port.Open(); port.WriteLine("AT"); port.WriteLine("AT+CMGF=1"); port.WriteLine("AT+CMGS=\"" + number + "\""); port.WriteLine(message); port.Write(new byte[] { (byte)26 }, 0, 1); } finally { if (port.IsOpen) { port.Close(); } } The differences I'm seeing in the trace from the serial port are At the start 0.00001844 aspnet_wp.exe IOCTL_SERIAL_SET_HANDFLOW USBSER001 SUCCESS Shake:1 Replace:43 XonLimit:4096 XoffLimit:4096 And at the very end 0.00061153 aspnet_wp.exe IOCTL_SERIAL_PURGE USBSER001 SUCCESS Purge: RXABORT RXCLEAR 0.00004442 aspnet_wp.exe IOCTL_SERIAL_PURGE USBSER001 SUCCESS Purge: TXABORT TXCLEAR Has anyone got any tips on how to iron out these issues? I also notice that the phone is not responding back to the application with any acknowledgement when I issue a command so I suspect the problem is with the connection, not those messages at the end.

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  • Feed paper on POS Printer C#

    - by evargas
    I've been trying to programatically feed the paper on a pos printer (Epson TM-U220D). The problem I have is that the last line of the document don't get printed, instead, it is printed as the first line of the next document printed. I tried POS for .NET sending the "ESC|flF" command, also tried to send the raw esc/pos command using the serial port, but it doesn't work. Any ideas?

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  • Typecasting a floating value or using the math.h floor* functions?

    - by nobody
    Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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  • Mercurial: Diff current source vs source at point in time

    - by Marcus
    I know how to view all changes in a changeset.. But let's say you update your source, you do a pull and you get 3 new changesets. How can you compare the current state of the remote repository (with the 3 changesets checked in) vs. the current source (on your local machine)? I'd like to do this using the visual diff tool which I currently have configured (Examdiff or Kdiff3).

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  • C/C++ - Convert 24-bit signed integer to float

    - by e-t172
    I'm programming in C++. I need to convert a 24-bit signed integer (stored in a 3-byte array) to float (normalizing to [-1.0,1.0]). The platform is MSVC++ on x86 (which means the input is little-endian). I tried this: float convert(const unsigned char* src) { int i = src[2]; i = (i << 8) | src[1]; i = (i << 8) | src[0]; const float Q = 2.0 / ((1 << 24) - 1.0); return (i + 0.5) * Q; } I'm not entirely sure, but it seems the results I'm getting from this code are incorrect. So, is my code wrong and if so, why?

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  • How to compare two floating-point values in shell script

    - by Reem
    I had to do a division in shell script and the best way was: result1=`echo "scale=3; ($var1 / $total) * 100"| bc -l` result2=`echo "scale=3; ($var2 / $total) * 100"| bc -l` but I want to compare the values of $result1 and $result2 Using if test $result1 -lt $result2 or if [ $result1 -gt $result2 ] didn't work :( Any idea how to do that?

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  • How to point to jdni.properties file to set properties in Java

    - by prosseek
    I can use System.getProperties() method to set properties in Java. System.getProperties().put("java.naming.factory.initial", "fr.dyade.aaa.jndi2.client.NamingContextFactory"); System.getProperties().put("java.naming.factory.host", "localhost"); System.getProperties().put("java.naming.factory.port", "16400"); How can I get the same effect by reading the properties stored in a file? When I have a jdni.properties with the following content: java.naming.factory.initial fr.dyade.aaa.jndi2.client.NamingContextFactory java.naming.factory.host localhost java.naming.factory.port 16400 How can I teach Java to read them as properties?

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  • Swap bits in c++ for a double

    - by hidayat
    Im trying to change from big endian to little endian on a double. One way to go is to use double val, tmp = 5.55; ((unsigned int *)&val)[0] = ntohl(((unsigned int *)&tmp)[1]); ((unsigned int *)&val)[1] = ntohl(((unsigned int *)&tmp)[0]); But then I get a warning: "dereferencing type-punned pointer will break strict-aliasing rules" and I dont want to turn this warning off. Another way to go is: #define ntohll(x) ( ( (uint64_t)(ntohl( (uint32_t)((x << 32) >> 32) )) << 32) | ntohl( ((uint32_t)(x >> 32)) ) ) val = (double)bswap_64(unsigned long long(tmp)); //or val = (double)ntohll(unsigned long long(tmp)); But then a lose the decimals. Anyone know a good way to swap the bits on a double without using a for loop?

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  • Streaming PDF via invocation of HTTPHandler using $.get into object element

    - by mythicdawn
    What I am trying to do is invoke an HTTPHandler via the $.get method of jQuery which will stream back a PDF and display it in a web page using an object element. My previous method of setting the src attribute of an IFrame to be the result of a handler invocation works, but I would like cross-browser completion notification, so have moved to using $.get(). Sample code: function buttonClick() { $.get("/PDFHandler.ashx", {}, function(data, textStatus, XMLHttpRequest) { var pdfObjectString = "<object data='' type='application/pdf' width='600' height='600'></object>"; var pdfObject = $(pdfObjectString); pdfObject.attr("data", data); $("#container").append(pdfObject); }); As you can see, I am attempting to stick the 'data' variable into an object element. This is not working (no error, PDF just doesn't display), presumably because the data that comes back is binary, yet the attr() method expects a string (I think). My question is thus: how can I invoke an HTTPHandler via $.get and somehow assign the data from the callback to the data attribute of an object?

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  • Dont know how to stop element in certain point

    - by user713190
    Im beginner and im experimenting on a website with fixed and relative postions, what i want to do is to stop bottom part when the two bottom lines(div .top_divider_line) touches nav menu(div .top_holder) here is the preview from site where im stuck. http://elexoj.com/test/ I think making it with jquery will be lot easier but i've no idea how to do it, i'll really appreciate your help. Thank You!

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