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• Computer science curriculum for non-CS major?

  - by Daniel

  Hi all, I would like to have some ideas for building up my foundation CS skills. I have started programming computers 10 years ago and have made a pretty good career out of it. However, I cannot stop thinking that the path that brought me here was very particular, and if something goes wrong (e.g. I get laid off) it would be harder to find a job here in the US on the same salary level, OR in a top company. The reason I say that is that I am a self-learner; my degree is not in Computer Science so although I master C/C++/Java, I do not have the formal CS and mathematical background that many other software developers (esp. here in the US) have. When I look at job interview questions from Apple, Google, Amazon, I have the impression that I'd flunk those technical interviews at some point. Don't get me wrong, I know my algorithms and data structures, but when things dive too deeply into the CS realm I am in trouble. What can I do to close the gap? I was thinking about a MSc in CS, but will I even UNDERSTAND what's going on there if I'm not a CS undergrad? Should I go back to basics and get a BSc in CS instead? I always tend to go into self-study mode when I want to learn new stuff, but I have the impression that I will need more formal education in CS if I want to have a shot at working at those kinds of companies. Thank you!

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• Formal definition for term "pure OO language"?

  - by Yauhen Yakimovich

  I can't think of a better place among SO siblings to pose such a question. Originally I wanted to ask "Is python a pure OO language?" but considering troubles and some sort of discomfort people experience while trying to define the term I decided to start with obtaining a clear definition for the term itself. It would be rather fair to start with correspondence by Dr. Alan Kay, who has coined the term (note the inspiration in biological analogy to cells or other living objects). There are following ways to approach the task: Give a comparative analysis by listing programming languages that exhibits certain properties unique and sufficient to define the term (although Smalltalk and Java are passing examples but IMO this way seems neither really complete or nor fruitful) Give a formal definition (or close to it, e.g. in more academic or mathematical style). Give a philosophical definition that would totally rely on semantical context of concrete language or a priori programming experience (there must be some chance of successful explanation by the community). My current version: "If a certain programing (formal) language that can (grammatically) differentiate between operations and operands as well as infer about the type of each operand whether this type is an object (in sense of OOP) or not then we call such a language an OO-language as long as there is at least one type in this language which is an object. Finally, if all types of the language are also objects we define such language to be pure OO-language." Would appreciate any possible improvement of it. As you can see I just made the definition dependent on the term "object" (often fully referenced as class of objects).

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• Would it be a good idea to work on letting people add arrays of numbers in javascript?

  - by OneThreeSeven

  I am a very mathematically oriented programmer, and I happen to be doing a lot of java script these days. I am really disappointed in the math aspects of javascript: the Math object is almost a joke because it has so few methods you can't use ^ for exponentiation the + operator is very limited, you cant add array's of numbers or do scalar multiplication on arrays Now I have written some pretty basic extensions to the Math object and have considered writing a library of advanced Math features, amazingly there doesn't seem to be any sort of standard library already out even for calculus, although there is one for vectors and matricies I was able find. The notation for working with vectors and matricies is really bad when you can't use the + operator on arrays, and you cant do scalar multiplication. For example, here is a hideous expression for subtracting two vectors, A - B: Math.vectorAddition(A,Math.scalarMultiplication(-1,B)); I have been looking for some kind of open-source project to contribute to for awhile, and even though my C++ is a bit rusty I would very much like to get into the code for V8 engine and extend the + operator to work on arrays, to get scalar multiplication to work, and possibly to get the ^ operator to work for exponentiation. These things would greatly enhance the utility of any mathematical javascript framework. I really don't know how to get involved in something like the V8 engine other than download the code and start working on it. Of course I'm afraid that since V8 is chrome specific, that without browser cross-compatibility a fundamental change of this type is likely to be rejected for V8. I was hoping someone could either tell me why this is a bad idea, or else give me some pointers about how to proceed at this point to get some kind of approval to add these features. Thanks!

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• OS X is based on the codex Gigas the devils bible: Android OS n 4.4 Dio Ra Egyptian deity why is that?

  - by user215250

  GUESS WHO? The Internet and all computers are based on a mathematical number system that seems to be 3, 4, 6, 8 and 10. The HTTP is 888P and UTF-8 and Windows 8 and 8 gigas of RAM(88) on a 64biTOS X-10 or Aten(satan) why is it allowed to be so evil and who all knows about it? Is this activity illegal and should I sew these companies for being involved in satanic practices? iC3 iC3 iC3 I do see XP (X) Chi and (P) Rho a monogram and symbol for Christ, consisting of the superimposed Greek letters. The X is ten, The X code, OS X(O Satan) and codex The Gigas the Devil bible and the P is Payne, The House of Payne in which God dwells. Windows 8, Google Android and Apples OS X are the foundation on which we operarte on the Internet and our Mobiles devices. What is it that these 3 companies have chosen to base their OS’s on such evil? Windows 8 is windows hate H8, HH and H8. Said to be the Devil. Google’s (UGLE) M the Masonic M behind Android OS.in 4.4 is Dio (R) DNA O Sin and 44 is the Devils name in Twain’s The Mysterious Stranger. Apple’s evil (i) OS X (ou-es-ten) O Satan them all beat (B8) considering Apple put their first product on the market for $666.66. The Holy Grail of computers they say. Your Excellency, Lord and King OS2 Eisus Uni Peg Unix: The Unicorn Pegasus Jesus Christ

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• Why doesn't libxml2 support XPath 2.0?

  - by Peter Krauss

  Libxml2 is the faster, stable and most popular "open DOM engine"... And the "XML C parser and toolkit of Gnome". The initial release of Libxml2 was September 1999, 13 years ago. XPath v1.0 was also released at 1999. XPath v2.0 became a recommendation on January 2007, 6 years ago. We can suppose that the Libxml2 community have time and people to develop a XPath2... So, what is the problem? Why doesn't libxml2 (or a "libxml2 fork" or an "experimental lib"!) support XPath 2.0? Some raised hypotheses to discussion at answers, Because Libxml2 community (and Gnome community) dislikes and have no motivation to develop something to XPath2 or xQuery. 1.1. XPath2 needs (by mathematical proof) a very heavy parser, much slower, etc. that is not suitable to real-world Libxml2 applications. 1.2. Other "ideologic" dislikes/motivations. Because it is written with C, and for XPath2 is better to develop with C++. Because the above hypothesis of "Libxml2 community have time and people" is false. Because XPath2 became stable in 2010 with its "Second Edition" release, and ~2.5 years is not (?) enough time.

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• Scheme vs Haskell for an Introduction to Functional Programming?

  - by haziz

  I am comfortable with programming in C and C#, and will explore C++ in the future. I may be interested in exploring functional programming as a different programming paradigm. I am doing this for fun, my job does not involve computer programming, and am somewhat inspired by the use of functional programming, taught fairly early, in computer science courses in college. Lambda calculus is certainly beyond my mathematical abilities, but I think I can handle functional programming. Which of Haskell or Scheme would serve as a good intro to functional programming? I use emacs as my text editor and would like to be able to configure it more easily in the future which would entail learning Emacs Lisp. My understanding, however, is that Emacs Lisp is fairly different from Scheme and is also more procedural as opposed to functional. I would likely be using "The Little Schemer" book, which I have already bought, if I pursue Scheme (seems to me a little weird from my limited leafing through it). Or would use the "Learn You a Haskell for Great Good" if I pursue Haskell. I would also watch the Intro to Haskell videos by Dr Erik Meijer on Channel 9. Any suggestions, feedback or input appreciated. Thanks. P.S. BTW I also have access to F# since I have Visual Studio 2010 which I use for C# development, but I don't think that should be my main criteria for selecting a language.

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• Calculating 3d rotation around random axis

  - by mitim

  This is actually a solved problem, but I want to understand why my original method didn't work (hoping someone with more knowledge can explain). (Keep in mind, I've not very experienced in 3d programming, having only played with the very basic for a little bit...nor do I have a lot of mathematical experience in this area). I wanted to animate a point rotating around another point at a random axis, say a 45 degrees along the y axis (think of an electron around a nucleus). I know how to rotate using the transform matrix along the X, Y and Z axis, but not an arbitrary (45 degree) axis. Eventually after some research I found a suggestion: Rotate the point by -45 degrees around the Z so that it is aligned. Then rotate by some increment along the Y axis, then rotate it back +45 degrees for every frame tick. While this certainly worked, I felt that it seemed to be more work then needed (too many method calls, math, etc) and would probably be pretty slow at runtime with many points to deal with. I thought maybe it was possible to combine all the rotation matrixes involve into 1 rotation matrix and use that as a single operation. Something like: [ cos(-45) -sin(-45) 0] [ sin(-45) cos(-45) 0] rotate by -45 along Z [ 0 0 1] multiply by [ cos(2) 0 -sin(2)] [ 0 1 0 ] rotate by 2 degrees (my increment) along Y [ sin(2) 0 cos(2)] then multiply that result by (in that order) [ cos(45) -sin(45) 0] [ sin(45) cos(45) 0] rotate by 45 along Z [ 0 0 1] I get 1 mess of a matrix of numbers (since I was working with unknowns and 2 angles), but I felt like it should work. It did not and I found a solution on wiki using a different matirx, but that is something else. I'm not sure if maybe I made an error in multiplying, but my question is: this is actually a viable way to solve the problem, to take all the separate transformations, combine them via multiplying, then use that or not?

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• jQuery - I'm getting unexpected outputs from a basic math formula.

  - by OllieMcCarthy

  Hi I would like to start by saying I'd greatly appreciate anyones help on this. I have built a small caculator to calculate the amount a consumer can save annually on energy by installing a ground heat pump or solar panels. As far as I can tell the mathematical formulas are correct and my client verified this yesterday when I showed him the code. Two problems. The first is that the calculator is outputting ridiculously large numbers for the first result. The second problem is that the solar result is only working when there are no zeros in the fields. Are there some quirks as to how one would write mathematical formulas in JS or jQuery? Any help greatly appreciated. Here is the link - http://www.olliemccarthy.com/test/johncmurphy/?page_id=249 And here is the code for the entire function - $jq(document).ready(function(){ // Energy Bill Saver // Declare Variables var A = ""; // Input for Oil var B = ""; // Input for Storage Heater var C = ""; // Input for Natural Gas var D = ""; // Input for LPG var E = ""; // Input for Coal var F = ""; // Input for Wood Pellets var G = ""; // Input for Number of Occupants var J = ""; var K = ""; var H = ""; var I = ""; // Declare Constants var a = "0.0816"; // Rate for Oil var b = "0.0963"; // Rate for NightRate var c = "0.0558"; // Rate for Gas var d = "0.1579"; // Rate for LPG var e = "0.121"; // Rate for Coal var f = "0.0828"; // Rate for Pellets var g = "0.02675"; // Rate for Heat Pump var x = "1226.4"; // Splittin up I to avoid error var S1 = ""; // Splitting up the calcuation for I var S2 = ""; // Splitting up the calcuation for I var S3 = ""; // Splitting up the calcuation for I var S4 = ""; // Splitting up the calcuation for I var S5 = ""; // Splitting up the calcuation for I var S6 = ""; // Splitting up the calcuation for I // Calculate H (Ground Sourced Heat Pump) $jq(".es-calculate").click(function(){ $jq(".es-result-wrap").slideDown(300); A = $jq("input.es-oil").val(); B = $jq("input.es-storage").val(); C = $jq("input.es-gas").val(); D = $jq("input.es-lpg").val(); E = $jq("input.es-coal").val(); F = $jq("input.es-pellets").val(); G = $jq("input.es-occupants").val(); J = ( A / a ) + ( B / b ) + ( C / c ) + ( D / d ) + ( E / e ) + ( F / f ) ; H = A + B + C + D + E + F - ( J * g ) ; K = ( G * x ) ; if ( A !== "0" ) { S1 = ( ( ( A / a ) / J ) * K * a ) ; } else { S1 = "0" ; } if ( B !== "0" ) { S2 = ( ( ( B / b ) / J ) * K * b ) ; } else { S2 = "0" ; } if ( C !== "0" ) { S3 = ( ( ( C / c ) / J ) * K * c ) ; } else { S3 = "0" ; } if ( D !== "0" ) { S4 = ( ( ( D / d ) / J ) * K * d ) ; } else { S4 = "0" ; } if ( E !== "0" ) { S5 = ( ( ( E / e ) / J ) * K * e ) ; } else { S5 = "0" ; } if ( F !== "0" ) { S6 = ( ( ( F / f ) / J ) * K * f ) ; } else { S6 = "0" ; } I = S1 + S2 + S3 + S4 + S5 + S6 ; if(!isNaN(H)) {$jq("span.es-result-span-h").text(H.toFixed(2));} else{$jq("span.es-result-span-h").text('Error: Please enter numerals only');} if(!isNaN(I)) {$jq("span.es-result-span-i").text(I.toFixed(2));} else{$jq("span.es-result-span-i").text('Error: Please enter numerals only');} }); });

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• Japanese Multiplication simulation - is a program actually capable of improving calculation speed?

  - by jt0dd

  On SuperUser, I asked a (possibly silly) question about processors using mathematical shortcuts and would like to have a look at the possibility at the software application of that concept. I'd like to write a simulation of Japanese Multiplication to get benchmarks on large calculations utilizing the shortcut vs traditional CPU multiplication. I'm curious as to whether it makes sense to try this. My Question: I'd like to know whether or not a software math shortcut, as described above is actually a shortcut at all. This is a question of programming concept. By utilizing the simulation of Japanese Multiplication, is a program actually capable of improving calculation speed? Or am I doomed from the start? The answer to this question isn't required to determine whether or not the experiment will succeed, but rather whether or not it's logically possible for such a thing to occur in any program, using this concept as an example. My theory is that since addition is computed faster than multiplication, a simulation of Japanese multiplication may actually allow a program to multiply (large) numbers faster than the CPU arithmetic unit can. I think this would be a very interesting finding, if it proves to be true. If, in the multiplication of numbers of any immense size, the shortcut were to calculate the result via less instructions (or faster) than traditional ALU multiplication, I would consider the experiment a success.

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• Vector vs Scalar velocity?

  - by Serguei Fedorov

  I am revamping an engine I have been working on and off on for the last few weeks to use a directional vector to dictate direction; this way I can dictate the displacement based on a direction. However, the issue I am trying to overcome is the following problem; the speed towards X and speed towards Y are unrelated to one another. If gravity pulls the object down by an increasing velocity my velocity towards the X should not change. This is very easy to implement if my speed is broken into a Vector datatype, Vector.X dictates one direction Vector.Y dictates the other (assuming we are not concerned about the Z axis). However, this defeats the purpose of the directional vector because: SpeedX = 10 SpeedY = 15 [1, 1] normalized = ~[0.7, 0.7] [0.7, 0.7] * [10, 15] = [7, 10.5] As you can see my direction is now "scaled" to my speed which is no longer the direction that I want to be moving in. I am very new to vector math and this is a learning project for me. I looked around a little bit on the internet but I still want to figure out things on my own (not just look at an example and copy off it). Is there way around this? Using a directional vector is extremely useful but I am a little bit stumped at this problem. I am sorry if my mathematical understanding maybe completely wrong.

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• How can Agile methodologies be adapted to High Volume processing system development?

  - by luckyluke

  I am developing high volume processing systems. Like mathematical models that calculate various parameters based on millions of records, calculated derived fields over milions of records, process huge files having transactions etc... I am well aware of unit testing methodologies and if my code is in C# I have no problem in unit testing it. Problem is I often have code in T-SQL, C# code that is a SQL stored assembly, and SSIS workflow with a good amount of logic (and outcomes etc) or some SAS process. What is the approach YOu use when developing such systems. I usually develop several tests as Stored procedures in a designed schema(TEST) and then automatically run them overnight and check out the results. But this is only for T-SQL. And Continous integration IS hard. But the problem is with testing SSIS packages. How do You test it? What is Your preferred approach for stubbing data into tables (especially if You need a lot data initialization). I have some approach derived over the years but maybe I am just not reading enough articles. So Banking, Telecom, Risk developers out there. How do You test your mission critical apps that process milions of records at end day, month end etc? What frameworks do You use? How do You validate that Your ssis package is Correct (as You develop it)/ How do You achieve continous integration in such an environment (Personally I never got there)? I hope this is not to open-ended question. How do You test Your map-reduce jobs for example (i do not use hadoop but this is quite similar). luke Hope that this is not too open ended

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• Enforcing Constraints Upon Data Documents of Various Formats

  - by Christopher Berman

  This seems like the sort of problem that must have been solved elegantly long ago, but I haven't the foggiest how to google it and find it. Suppose you're maintaining a large legacy system, which has a large collection of data (tens of GB) of various formats, including XML and two different internal configuration formats. Suppose further that there are abstract rules governing the values these files may or may not contain. EXAMPLE: File A defines the raw, mathematical data pertaining to the aerodynamics of a car for consumption of the physics component of the system. File B contains certain values from File A in an easily accessible, XML hierarchy for consumption of a different component of the system. There exists, therefore, an abstract rule (or constraint) such that the values from File B must match the values from File A. This is probably the simplest constraint that can be specified, but in practice, the constraints between files can become very complicated indeed. What is the best method for managing these constraints between files of arbitrary formats, short of migrating it over to an RDBMS (which simply isn't feasible for the foreseeable future)? Has this problem been solved already? To be more specific, I would expect the solution to at least produce notifications of violated constraints; the solution need not resolve the constraints. ============================== Sample file structures File A (JeepWrangler2011.emv): MODEL JeepWrangler2011 { EsotericMathValueX 11.1 EsotericMathValueY 22.2 EsotericMathValueZ 33.3 } File B (JeepWrangler2011.xml): <model name="JeepWrangler2011"> <!--These values must correspond File A's EsotericMathValues--> <modelExtent x="11.1" y="22.2" z="33.3"/> [...] </model>

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• Generic rule parser for RPG board game rules - how to do it?

  - by burzum

  I want to build a generic rule parser for pen and paper style RPG systems. A rule can involve usually 1 to N entities 1 to N roles of a dice and calculating values based on multiple attributes of an entity. For example: Player has STR 18, his currently equipped weapon gives him a bonus of +1 STR but a malus of DEX -1. He attacks a monster entity and the game logic now is required to run a set of rules or actions: Player rolls the dice, if he gets for example 8 or more (base attack value he needs to pass is one of his base attributes!) his attack is successfully. The monster then rolls the dice to calculate if the attack goes through it's armor. If yes the damage is taken if not the attack was blocked. Besides simple math rules can also have constraints like applying only to a certain class of user (warrior vs wizzard for example) or any other attribute. So this is not just limited to mathematical operations. If you're familiar with RPG systems like Dungeon and Dragons you'll know what I'm up to. My issue is now that I have no clue how to exactly build this the best possible way. I want people to be able to set up any kind of rule and later simply do an action like selecting a player and a monster and run an action (set of rules like an attack). I'm asking less for help with the database side of things but more about how to come up with a structure and a parser for it to keep my rules flexible. The language of choice for this is php by the way.

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• What is the R Language?

  - by TATWORTH

  I encountered the R Language recently with O'Reilly books and while from the context I knew it was a language for dealing with statistics, doing a web search for the support web site was futile. However I have now located the web site and it is at http://www.r-project.org/R is a free language available for a number of platforms including windows. CRAN mirrors are available at a number of locations worldwide.Here is the official description:"R is a language and environment for statistical computing and graphics. It is a GNU project which is similar to the S language and environment which was developed at Bell Laboratories (formerly AT&T, now Lucent Technologies) by John Chambers and colleagues. R can be considered as a different implementation of S. There are some important differences, but much code written for S runs unaltered under R. R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, ...) and graphical techniques, and is highly extensible. The S language is often the vehicle of choice for research in statistical methodology, and R provides an Open Source route to participation in that activity. One of R's strengths is the ease with which well-designed publication-quality plots can be produced, including mathematical symbols and formulae where needed. Great care has been taken over the defaults for the minor design choices in graphics, but the user retains full control. R is available as Free Software under the terms of the Free Software Foundation's GNU General Public License in source code form. It compiles and runs on a wide variety of UNIX platforms and similar systems (including FreeBSD and Linux), Windows and MacOS."

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• Spherical to Cartesian Coordinates

  - by user1258455

  Well I'm reading the Frank's Luna DirectX10 book and, while I'm trying to understand the first demo, I found something that's not very clear at least for me. In the updateScene method, when I press A, S, W or D, the angles mTheta and mPhi change, but after that, there are three lines of code that I don't understand exactly what they do: // Convert Spherical to Cartesian coordinates: mPhi measured from +y // and mTheta measured counterclockwise from -z. float x = 5.0f*sinf(mPhi)*sinf(mTheta); float z = -5.0f*sinf(mPhi)*cosf(mTheta); float y = 5.0f*cosf(mPhi); I mean, this explains that they do, it says that it converts the spherical coordinates to cartesian coordinates, but, mathematically, why? why the x value is calculated by the product of the sins of both angles? And the z by the product of the sine and cosine? and why the y just uses the cosine? After that, those values (x, y and z) are used to build the view matrix. The book doesn't explain (mathematically) why those values are calculated like that (and I didn't find anything to help me to understand it at the first Part of the book: "Mathematical prerequisites"), so it would be good if someone could explain me what exactly happen in those code lines or just give me a link that helps me to understand the math part. Thanks in advance!

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• Best way to calculate unit deaths in browser game combat?

  - by MikeCruz13

  My browser game's combat system is written and mechanically functioning well. It's written in PHP and uses a SQL database. I'm happy with the unit balance in relation to one another. I am, however, a little worried about how I'm calculating unit deaths when one player attacks another because the deaths seem to pile up a little fast for my taste. For this system, a battle doesn't just trigger, calculate winner, and end. Instead, it is allowed to go for several rounds (say one round every 15 mins.) until one side passes a threshold of being too strong for the other player and allows players to send reinforcements between rounds. Each round, units pair up and attack each other. Essentially what I do is calculate the damage: AP = Attack Points HP = Hit Points Units AP * Quantity * Random Factors * other factors (such as attrition) I take that and divide by the defending unit's HP to find the number of casualties of defending units. So, for example (simplified to take out some factors), if I have: 500 attackers with 50 AP vs 1000 defenders with 100 HP = 250 deaths. I wonder if that last step could be handled better to reduce the deaths piling up. Some ideas: I just change all the units with more HP? I make sure to set the Attacking unit's AP to be a max of the defender's HP to make sure they only kill 1 unit. (is that fair if I have less huge units vs many small units?) I spread the damage around more by including the defending unit's quantity more? i.e. in that scenario some are dead and some are 50% damage. (How would I track this every round?) Other better mathematical approaches?

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• How well do graduates from top universities perform and how does it feel compare to the rest of the world?

  - by Amumu

  I always have impressions to those who got admitted into top Universities like MIT, Standford... for studying Engineering. I don't actually know what they are doing in the University or what they will do, but I always feel they can perform higher level tasks with more complexities. I always think that they are good at create and applying mathematical model in real life and I tend to agree: If you can't apply math, it's your problems, not math. I am a junior software engineer on embedded devices. I am learning more on Linux kernel and low level stuffs. Even so, my will is not strong enough to pursue technical path forever, with a final purpose is to create something significant on my own. May I have a chance to get on their level if I keep learning through experience and self-study? In my opinion, Math is the must have requirement, since it seems that programs on those Universities are very Math oriented. Without very strong math skill, how can one perform good in science and researching beyond making regular business products?

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• Finite Numbers and ExplorerCanvas

  - by PhubarBaz

  I was working on my online mathematical graphing application, CloudGraph, and trying to make it work in IE. The app uses the HTML5 canvas element to draw graphs. Since IE doesn't support canvas yet I use ExplorerCanvas to provide that support for IE. However, it seems that when using excanvas, if you try to moveTo or drawTo a point that is not finite it loses it's mind and stops drawing anything else after that. I had no such problems in Firefox or Chrome so it took me awhile to figure out what was going on. Next I discovered that I needed a way to check if a variable was NaN or Inifinity or any other non-finite value so I could avoid calling moveTo() in that case. I started writing a long if statement, then I thought there has to be a better way. Sure enough there was. There just happens to be an isFinite() function built into Javascript just for this purpose. Who knew! It works great. Another difference I discovered with excanvas is that you must specify a starting point using a moveTo() when beginning a drawing path. Again, Chrome and Firefox are a lot more forgiving in this area so it took me a while to figure out why my lines weren't drawing. But, all is happy now and I'm a little wiser to the ways of the canvas.

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• Cube rotation DX10

  - by German

  Well I'm reading the Frank's Luna DirectX10 book and, while I'm trying to understand the first demo, I found something that's not very clear at least for me. In the updateScene method, when I press A, S, W or D, the angles mTheta and mPhi change, but after that, there are three lines of code that I don't understand exactly what they do: // Convert Spherical to Cartesian coordinates: mPhi measured from +y // and mTheta measured counterclockwise from -z. float x = 5.0f*sinf(mPhi)*sinf(mTheta); float z = -5.0f*sinf(mPhi)*cosf(mTheta); float y = 5.0f*cosf(mPhi); I mean, this explains that they do, it says that it converts the spherical coordinates to cartesian coordinates, but, mathematically, why? why the x value is calculated by the product of the sins of both angles? And the z by the product of the sine and cosine? and why the y just uses the cosine? After that, those values (x, y and z) are used to build the view matrix. The book doesn't explain (mathematically) why those values are calculated like that (and I didn't find anything to help me to understand it at the first Part of the book: "Mathematical prerequisites"), so it would be good if someone could explain me what exactly happen in those code lines or just give me a link that helps me to understand the math part. Thanks in advance!

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• MathML or OMML to PNG w/ .NET?

  - by charliedigital

  Are there any libraries which take MathML (or, even more preferably, OMML) and outputs a .PNG file? I am putting together an export process for .docx files and, as a part of this process, I'd like to extract equations and render them as .PNG files. Word 2007 does this natively when you save a document for the web, but so far, I have not been able to find a way to do this programmatically (if anyone has an answer for that, it would be even better). So the next best thing is to take the OMML and use the Microsoft provided XSL stylesheets and transform them to MathML. Unfortunately, I haven't been able to find any (working) rendering libraries for either MathML or OMML. If there aren't any pure .NET libraries for this, I'll settle for just about anything that I can call from a commandline to output a .PNG from either MathML or OMML.

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• Calculate initial velocity to move a set distance with inertia

  - by Bodyscanner

  Hello, I want to move something a set distance. However in my system there is inertia/drag/negative accelaration. I'm using a formula like this for it: velocity = oldVelocity + ((velocity - oldVelocity * inertia) where inertia is a fractional value like 0.25 So to move the item a set distance, I need to calculate what the initial velocity should be (I know what all the other values are). I've been looking at Equations of motion (http://en.wikipedia.org/wiki/Equations_of_motion) but can't work out what the correct one for my problem is... Any ideas? Thanks!

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• iTunes Visualization -- What type of code is it written in and what does that code look like?

  - by Christopher Altman

  Being a web developer, I know how event driven user interfaces are written, but do not have insight into other families of code (embedded software like automotive software, automation software on assembly lines, drivers, or the crawling lower-thirds on CNN, etc.) I was looking at the iTunes visualizer (example) and am curious: What code is used to write the visualizer? Objective C? Does it use Core Animation? What type of abstraction does that library offer? What does the code look like? Is it a list of mathematical equations for producing the crazy graphics? Is it a list of key frames with tweening? Is there an array of images, fractals, worm holes, flowers, sparkles, and some magic mixes them together. Or something totally different? I am not looking for a tutorial, just an understanding of how something very different than web development works. Oh yah, I know iTunes is closed source, so all of this is conjecture.

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• Inverse Logistic Function / Reverse Sigmoid Function

  - by Chanq

  I am currently coding up a fuzzy logic library in java. I have found the equations for all the standard functions - Grade, inverseGrade, Triangle, Trapezoid, Gaussian. However, I can't find the inverse of the sigmoid/ logistic function. The way I have written the logistic function is java is : //f(x) = 1/(1+e(-x)) public double logistic(double x){ return (1/(1+(Math.exp(-x))); } But I can't work out or find the inverse anywhere. My algebraic/calculus abilities are fairly limited, hence why I haven't been able to work out the inverse of the function. Any hints or pointers would be a big help. Thanks

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• Deploying Excel 2003 VSTO Workbook using Sharepoint for versioning control

  - by KClough

  I have an excel 2003 vsto workbook that I would like to make available via sharepoint for version control. Ideally it could be checked in/out by non-developers for tweaking excel equations, and I would be able to deploy the compiled dlls somewhere else when I need to update the managed VSTO code. I understand I may need to use some clickonce functionality as well so when a user first views the sheet they get all the necessary full-trust permissioning. Also, it is my understanding that for a user to use the vsto functionality in an excel 2003 vsto workbook, they must have the compiled dll in thier GAC, is this true? When testing I get trust exceptions otherwise.

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• Graphing a line and scatter points using Matplotlib?

  - by Patrick O'Doherty

  Hi guys I'm using matplotlib at the moment to try and visualise some data I am working on. I'm trying to plot around 6500 points and the line y = x on the same graph but am having some trouble in doing so. I can only seem to get the points to render and not the line itself. I know matplotlib doesn't plot equations as such rather just a set of points so I'm trying to use and identical set of points for x and y co-ordinates to produce the line. The following is my code from matplotlib import pyplot import numpy from pymongo import * class Store(object): """docstring for Store""" def __init__(self): super(Store, self).__init__() c = Connection() ucd = c.ucd self.tweets = ucd.tweets def fetch(self): x = [] y = [] for t in self.tweets.find(): x.append(t['positive']) y.append(t['negative']) return [x,y] if __name__ == '__main__': c = Store() array = c.fetch() t = numpy.arange(0., 0.03, 1) pyplot.plot(array[0], array[1], 'ro', t, t, 'b--') pyplot.show() Any suggestions would be appreciated, Patrick

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