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  • How to improve problem solving skills/programming skills

    - by kaibuki
    Hi All, I am new to programming, and have been given many interviews for jobs, but what I lag is the concepts and skills of general problem solving not respect to any particular programming language. are there any books or material available which can help me upgrade my programming skills. looking forward for you guys to share your views. Thanks a millions.. Kai

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  • Can someone recommend a resource/site/book to improve problem solving skills

    - by kjm
    I am a reasonably experienced developer (.NET, c#, asp.NET etc) but I'd like to hone my problem solving skills. I find that when I come up against a complex problem I sometimes implement a solution that I feel could have been better had I analyzed the problem in a different way. Ideally what I am looking for is a resource of some type that has 'practice problems and solutions' as I think my skills will only get better by practicing this more and adopting better practices. I hope my question is not to vague and I wont get upset with people answering with opinions etc.. thanks

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  • Solving a math problem/expression, which is a string, in PHP

    - by Koning WWWWWWWWWWWWWWWWWWWWWWW
    The user can enter a math problem (expression) like 5 + 654, 6 ^ 24, 2!, sqrt(543), log(54), sin 5, sin(50). After some reformatting (e.g. change sin 5 into sin(5)), and doing an eval, PHP gives me the right result: $problem = "5 + 5324"; eval("$result = " . $problem); echo $problem . " = " . $result; However, this is quite unsafe: /* If you read this, please, plz don't be stupid and DO NOT EXECUTE this code!!!!! */ $problem = "shell_exec('rm -rf /')"; eval("$result = " . $problem); /* Nukes system */ echo $problem . " = " . $result; Can anyone point me in the right direction parsing and solving a math question like the examples above, which is safe? Thanks.

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  • Abstraction: The War between solving the problem and a general solution.

    - by Bryan Harrington
    As a programmer, I find myself in the dilemma where I want make my program as abstract and as general as possible. Doing so usually would allow me to reuse my code and have a more general solution for a problem that might (or might not) come up again. Then this voice in my head says, just solve the problem dummy its that easy! Why spend more time than you have to? We all have indeed faced this question where Abstraction is on your right shoulder and Solve-it-stupid sits on the left. Which to listen to and how often? What is your strategy for this? Should you abstract everything?

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  • Equation parsing in Python

    - by MikeCroucher
    How can I (easily) take a string such as 'sin(x)*x^2' which might be entered by a user at runtime and produce a python function that could be evaluated for any value of x? Does anyone know of any libraries or modules that takes care of this sort of thing?

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  • Efficient algorithm to generate all solutions of a linear diophantine equation with ai=1

    - by Ben
    I am trying to generate all the solutions for the following equations for a given H. With H=4 : 1) ALL solutions for x_1 + x_2 + x_3 + x_4 =4 2) ALL solutions for x_1 + x_2 + x_3 = 4 3) ALL solutions for x_1 + x_2 = 4 4) ALL solutions for x_1 =4 For my problem, there are always 4 equations to solve (independently from the others). There are a total of 2^(H-1) solutions. For the previous one, here are the solutions : 1) 1 1 1 1 2) 1 1 2 and 1 2 1 and 2 1 1 3) 1 3 and 3 1 and 2 2 4) 4 Here is an R algorithm which solve the problem. library(gtools) H<-4 solutions<-NULL for(i in seq(H)) { res<-permutations(H-i+1,i,repeats.allowed=T) resum<-apply(res,1,sum) id<-which(resum==H) print(paste("solutions with ",i," variables",sep="")) print(res[id,]) } However, this algorithm makes more calculations than needed. I am sure it is possible to go faster. By that, I mean not generating the permutations for which the sums is H Any idea of a better algorithm for a given H ?

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  • Hard problem - need help for solving

    - by dada
    I don't want you to solve this problem for me, i just want to ask for some ideas. This is the input below, and it represents a map. The 'x' represents land, and the dots - water. So with the 'x' you can represent 'islands' on the map. xxx.x...xxxxx xxxx....x...x ........x.x.x ..xxxxx.x...x ..x...x.xxx.x ..x.x.x...x.. ..x...x...xxx ...xxxxxx.... x............ As you can see, there are some islands which are closed, i.e. if some boat is inside its territory, it won't be able to get out, for ex: ..xxxxx. ..x...x. ..x.x.x. ..x...x. ..xxxxx. And there are some open islands which is possible to get out of them, ex: .xxxxx .x...x .x.x.x .xxx.x The problem is this: For a given NxM map like those above, calculate howm any of the islands are open, and how many are closed. I repeat: I don't want you to solve it, just need some sugestions, ideas for solving. thanks

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  • Can I trust the Basic schedule equation?

    - by Steve Campbell
    I've been reading Steve McConnell's demystifying the black art of estimating book, and he gives an equation for estimating nominal schedule based on Person-months of effort: ScheduleInMonths = 3.0 x EffortInMonths ^ (1/3) Per the book, this is very accurate (within 25%), although the 3.0 factor above varies depending on your organization (typically between 2 and 4). It is supposedly easy to use historical projects in your organization to derive an appropriate factor for your use. I am trying to reconcile the equation against Agile methods, using 2-6 week cycles which are often mini-projects that have a working deliverable at the end. If I have a team of 5 developers over 4 weeks (1 month), then EffortInMonths = 5 Person Months. The algorithm then outputs a schedule of 3.0 x 5^(1/3) = 5 months. 5 months is much more than 25% different than 1 month. If I lower the 3.0 factor to 0.6, then the algorthim works (outputs a schedule of approx 1 month). The lowest possible factor mentioned in the book through is 2.0. Whats going on here? I want to trust this equation for estimating a "traditional" non-agile project, but I cannot trust it when it does not reconcile with my (agile) experience. Can someone help me understand?

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  • In R, how do you get the best fitting equation to a set of data?

    - by Matherion
    I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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  • problem solving [closed]

    - by Suresh S
    Problem Statement The Sports Associations in India (SAI) wants to choose 2 teams of 4 people each to send to Asian games. There are 13 people who want to be members of the teams. The SAI tries grouping them in various ways to see which athletes perform well together. Each grouping gets one test run on the test track and their time is recorded. Your task is to help the SAI choose two disjoint teams of 4 such that the sum of their practice times is minimal. Input There will be several input instances. The first line of each instance gives the total number of practice runs. This will be followed by n lines. Each of those lines will contain 5 numbers: p1 p2 p3 p4 t t is the time taken (in milliseconds) by the team consisting of p1, p2, p3 and p4. The time taken will not be more than 2 minutes. The end of the input will be indicated by a line with n=0. Output Output the best total and the two teams that you choose. If it is impossible to choose two disjoint teams from the test runs given, output -1. Sample Input 6 1 2 3 4 30000 10 11 12 13 15000 5 6 7 8 37800 1 5 10 12 20000 5 6 9 11 43000 1 9 12 13 11000 3 1 4 7 9 10000 3 5 7 11 17890 6 7 12 13 20000 0 Sample Output 45000 -1 Input to the problem 40 2 8 11 9 15532 1 13 11 9 57629 10 12 1 5 43406 6 10 1 2 43904 8 3 4 11 12473 6 12 5 11 19826 3 9 10 11 48347 6 12 13 1 45854 5 4 9 7 34452 9 8 12 2 5596 4 10 2 7 6778 3 6 8 5 32858 13 12 8 6 42457 12 9 2 5 49530 6 8 10 7 51453 1 3 11 9 18620 6 2 5 11 5153 4 1 9 8 37336 10 5 1 12 59524 4 5 3 2 1318 2 13 6 8 7839 12 4 9 5 30697 4 10 13 1 25249 4 2 9 13 52359 8 11 1 9 36437 7 5 11 6 58522 9 1 12 6 58837 7 6 8 5 37826 13 1 11 3 1841 11 3 5 13 50000 2 8 7 12 10137 1 4 12 5 32558 8 5 6 7 39021 1 7 10 13 5979 9 2 11 6 29661 13 12 9 7 7219 12 1 11 9 37354 5 1 10 9 47948 8 1 2 10 11071 2 11 1 8 3074 80 3 5 8 10 37873 1 2 3 5 27633 10 13 3 11 8645 13 1 9 6 2167 5 11 13 8 30862 8 7 9 6 47591 3 11 13 8 33823 2 13 7 5 36668 12 3 11 6 53711 6 13 3 7 52412 3 6 7 5 3850 1 5 11 12 35483 1 7 6 10 50943 11 3 6 8 40191 12 8 13 7 4529 4 10 5 1 43280 4 12 10 5 35142 12 4 5 10 37242 9 7 13 2 2661 3 9 2 10 453 3 8 12 9 12479 3 10 11 5 30047 9 1 11 2 40883 6 5 1 2 8774 11 7 9 1 37701 8 3 4 6 32970 4 12 7 10 55109 8 11 13 12 44713 2 10 8 5 37763 13 10 12 2 53628 7 2 5 10 53197 3 2 1 11 14916 1 2 3 10 50756 3 13 5 6 6959 10 6 1 4 2948 4 7 13 9 14146 8 13 10 2 16784 3 2 6 5 30337 1 6 7 8 14239 2 6 11 5 13749 12 1 10 5 30827 4 6 11 8 18780 9 10 8 5 6336 7 9 1 3 3101 10 3 4 13 56678 7 6 3 8 8258 11 7 12 6 19046 13 6 9 8 46356 9 5 11 13 56570 9 1 10 5 6193 8 6 9 11 16854 3 7 4 9 53573 8 12 10 1 28135 10 3 8 4 31411 11 1 3 12 34534 8 6 4 13 3527 1 6 10 9 52307 11 7 1 12 2886 12 11 1 6 17659 13 5 6 8 48834 11 2 1 10 52951 3 9 13 7 21054 1 5 11 9 14507 11 5 12 4 42040 1 6 12 7 46414 5 12 3 10 26239 6 10 7 8 40762 8 11 6 10 38538 13 1 10 7 31140 9 10 13 4 34164 13 6 7 12 49696 6 13 3 5 36003 8 9 13 6 58409 3 10 7 9 20693 2 1 11 12 22653 5 8 4 7 49888 5 3 2 11 29911 8 12 6 9 30964 8 3 13 6 23597 4 1 6 7 31657 4 6 8 7 13 33639 13 8 10 3 27863 5 2 1 12 1408 4 11 1 12 59010 63 10 11 9 8 23611 10 8 6 11 12410 4 6 7 9 44390 8 4 1 6 16543 1 2 8 10 37452 11 12 6 13 28968 11 12 2 8 59617 1 9 11 2 28631 11 6 5 1 27251 2 7 10 4 42503 7 8 10 3 13673 9 13 11 7 30308 6 1 12 9 4888 13 1 9 8 19475 8 7 3 5 34187 8 1 12 3 46266 6 10 12 5 32855 3 7 13 1 38427 2 5 13 3 59487 6 11 1 13 2098 1 4 13 6 22239 13 7 12 3 28703 12 3 7 4 32 9 8 2 13 35271 10 13 6 12 36422 12 6 9 8 44303 1 9 13 11 22962 11 13 6 12 39518 5 6 13 11 47909 4 13 1 8 10654 11 8 12 4 31956 7 12 9 13 35923 4 9 3 2 34736 13 2 10 1 22945 7 10 8 13 36947 1 4 12 13 19432 7 12 13 4 48718 9 5 13 11 18827 11 2 1 12 45444 8 12 6 13 33175 4 2 11 13 56186 2 9 3 11 33218 12 13 8 1 50727 13 1 8 2 48138 7 1 5 3 1926 6 4 10 1 40997 11 3 1 4 26033 6 10 13 1 40988 11 12 5 4 25199 4 3 1 10 23498 3 6 12 7 24306 13 10 12 3 53255 3 13 4 12 14517 7 10 9 3 29925 9 11 12 13 28333 3 5 13 6 13602 13 12 9 6 10394 8 4 12 6 57471 9 3 4 7 34723 11 9 5 3 38480 12 9 10 11 48048 4 3 6 7 31884 2 10 4 5 57654 86 1 6 5 13 56577 6 8 2 5 20429 11 13 9 3 2243 3 1 10 12 55231 9 5 7 8 29964 5 11 8 1 29624 6 9 3 1 43055 12 13 10 8 52132 10 8 4 1 5729 7 3 6 8 53097 11 12 7 1 18711 12 7 6 13 44397 10 12 5 7 53574 5 3 4 13 27078 11 2 5 10 43623 3 7 1 8 57350 10 12 4 9 19752 5 13 9 3 59380 4 7 13 6 32575 7 5 6 11 13593 13 7 12 6 38282 13 7 6 2 45430 6 2 5 10 38082 2 11 13 7 53557 10 6 7 13 40461 6 11 7 1 22007 4 7 2 3 22386 9 7 11 10 35337 2 6 11 7 4129 6 13 5 3 31813 1 11 6 9 11749 5 11 8 13 21858 5 12 9 11 2470 13 10 6 11 14503 8 4 1 3 10783 1 10 12 7 47116 11 1 8 10 25034 8 1 4 9 23350 3 10 1 9 56717 13 2 8 12 5825 12 3 13 7 35628 10 6 1 12 26901 2 13 3 5 2775 1 8 9 7 1294 7 13 12 2 48170 11 9 13 1 34311 9 6 3 13 30663 8 3 10 6 5853 1 10 2 4 19880 9 2 3 12 48990 3 7 11 4 51558 8 13 2 4 9698 9 4 5 1 6834 3 4 12 2 20941 11 3 9 7 40108 13 11 2 4 2594 8 9 10 13 12242 1 8 10 5 42413 7 1 11 3 17779 1 5 8 3 6934 4 9 8 11 10235 8 11 10 2 18879 11 4 8 2 12691 9 7 5 2 44947 3 2 5 4 30042 2 7 12 4 27185 6 5 10 1 28695 12 9 1 5 53813 8 12 9 3 24719 6 1 4 11 22716 1 13 10 8 39981 12 11 5 2 22412 6 11 2 4 14457 4 11 5 3 39658 10 11 2 1 33056 1 3 6 9 16958 6 11 12 7 50779 8 10 6 13 24824 7 10 1 13 35692 13 4 8 9 32885 7 6 4 3 10948 4 5 7 1 36875 5 10 6 7 58746 10 7 8 12 39453 8 4 12 1 46674 11 3 1 8 48103 0

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  • Solving programming problems or contributing code?

    - by nischayn22
    What are the best skills to develop for a college graduate?? Should one spend hours/days trying to solve problems on codechef or topcoder or contribute code to open source organizations? My personal experience says solving problems teaches you how to make optimal code and learn new programming techniques (which someone else has researched and made available) to solve problems, whereas contributing to open source teaches you how to organize code (so others can work on it), use coding conventions and make "real" use of what you have learnt so far, blah blah!! Also another thing to note is that many companies are hiring today based on one's problem solving skills (Is this something I should worry about?) P.S. I have done little of online problem solving and little of code contribution (via GSoC), but left confused what I should continue doing (as doing both simultaneously isn't easy).

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  • Equation solver project

    - by Victor Barbu
    I would like to start a project destinated to students. My application has to solve any kind of equation, passed by the user as a string, exactly like in Matlab solve function. How shluld I do this? What programming language is the best for this purpose? Thanks in advance. P.S This is a screenshot made in Matlab. This is how I would like the user to insert and receive the answer: Another example:

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  • Equation / formula to determine an objects position on an ellipitcal path

    - by David Murphy
    I'm making a space game, as such I need objects to follow an elliptical path (orbit). I've worked out how to calculate all the important aspects of my orbits, the only remaining thing is how to have an object follow it. My Orbit class contains the major, minor (and by extension semi-major,semi-minor) lengths. The focii radius, area and circumference even. What is the equation to determine an objects x/y position (only need 2D) on an ellipse with a certain speed after a period of time. Basically, every frame I want to update the position based on the amount of elapsed time. I would like to have the speed along the path speed up and slow down according to the distance from the object it's orbiting, but not sure how to factor this in to the above given that at any point in time the speed has changed from it's previous speed. EDIT I can't answer my own question. But I found the question and answer is already on stackexchange: Kepler orbit : get position on the orbit over time

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  • Is problem solving of puzzles/logic tests a skill that can be developed with practise or only someth

    - by dotnetdev
    Programming is essentially problem solving/using a lot of logic. With solving puzzles (like the ones recruiters like MS etc ask), is this a skill that can be developed with practise or is it a skill that only someone who is gifted has (I assume the former as many people can pass these tests)? Even so, I keep thinking it is a special skill for someone gifted, not for someone with a lot of practise. I guess that with practise you are perhaps more open-minded and start to think out of the box more (solving technical problems in development may also foster this mindset perhaps). Thanks

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  • Problem solving/ Algorithm Skill is a knack or can be developed with practice?

    - by KaluSingh Gabbar
    Every time I start a hard problem and if can not figure out the exact solution or can not get started, I get into this never ending discussion with myself, as below: That problem solving/mathematics/algorithms skills are gifted (not that you can learn by practicing, by practice, you only master the kind of problems that you already have solved before) only those who went to good schools can do it, as they learned it early. What are your thoughts, can one achieve awesomeness in problem solving/algorithms just by hard work or you need to have that extra-gene in you?

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  • Adding an equation or formula to a figure caption in LaTeX

    - by gotgenes
    I have a figure in LaTeX with a caption to which I need to add a formula (equation* or displaymath environments). For example: \documentclass[12pt]{article} \begin{document} \begin{figure}[tbph] \begin{center} %... \end{center} \caption{As you can see \begin{displaymath}4 \ne 5\end{displaymath} } \label{fig:somefig} \end{figure} \end{document} This makes pdflatex angry, though it will produce a PDF. ! Argument of \@caption has an extra }. <inserted text> \par l.9 } What's the right way to go about adding an equation to a figure caption? NOTE: Please do not suggest simply using the $ ... $ math environment; the equation shown is a toy example; my real equation is much more intricate. See also: Adding a caption to an equation in LaTeX (the reverse of this question)

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  • How I improve my problem-solving ability

    - by gcc
    How we can improve our problem-solving ability ? Every one says same thing "real programmer knows how to handle real problem.", but they forget something how they take this ability, or where ( I know in school, no one gives us any ability, of course in my opinion. ) If you have any idea except above ones, feel free when you give an advice solve more problem do more exercise, write code, search google then write more ... For me, my question is like "Use complex/known library instead of using your own." In other words, I want your experience, book recommendation, web page

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  • Fast language for problem solving? [closed]

    - by Friend of Kim
    I learned PHP to make websites. After some years I've started using programming for solving what is difficult tasks for my level. Now I want to make a program that solves equations. (I want to write it myself, not use an API. Because I'm doing this for the sake of the challenge, not for the result..) Because of this, I'm going to learn a new and faster/better language. It's going to be C++, Java, Python or C#. What are the benefits of each language, and which language is best for speed compared to speed of writing and readability? Using C would be lightning fast, but the lack of OO is making for more complex code and reduces the readability, for example..

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  • Vector transform equation explanation

    - by cyberdemon
    I'm trying to understand the maths of moving points in a 3d space by making a game written in C#. I'm looking at this wolfire blog series which explains some basic 3d maths. I've read the first two parts but am stuck on the 3rd. I know it's all really rudimentary stuff but I find Googling for help with equations really hard. The one I'm struggling with is: 0*(0.66,0.75) + 2*(-0.75, 0.66) = (-1.5, 1.3) How can anything multiplied by 0 not be 0? So my question is how does this look in code: x(a,b) + y(c,d) I know it's basic stuff but I just can't see it.

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  • Solving Big Problems with Oracle R Enterprise, Part I

    - by dbayard
    Abstract: This blog post will show how we used Oracle R Enterprise to tackle a customer’s big calculation problem across a big data set. Overview: Databases are great for managing large amounts of data in a central place with rigorous enterprise-level controls.  R is great for doing advanced computations.  Sometimes you need to do advanced computations on large amounts of data, subject to rigorous enterprise-level concerns.  This blog post shows how Oracle R Enterprise enables R plus the Oracle Database enabled us to do some pretty sophisticated calculations across 1 million accounts (each with many detailed records) in minutes. The problem: A financial services customer of mine has a need to calculate the historical internal rate of return (IRR) for its customers’ portfolios.  This information is needed for customer statements and the online web application.  In the past, they had solved this with a home-grown application that pulled trade and account data out of their data warehouse and ran the calculations.  But this home-grown application was not able to do this fast enough, plus it was a challenge for them to write and maintain the code that did the IRR calculation. IRR – a problem that R is good at solving: Internal Rate of Return is an interesting calculation in that in most real-world scenarios it is impractical to calculate exactly.  Rather, IRR is a calculation where approximation techniques need to be used.  In this blog post, we will discuss calculating the “money weighted rate of return” but in the actual customer proof of concept we used R to calculate both money weighted rate of returns and time weighted rate of returns.  You can learn more about the money weighted rate of returns here: http://www.wikinvest.com/wiki/Money-weighted_return First Steps- Calculating IRR in R We will start with calculating the IRR in standalone/desktop R.  In our second post, we will show how to take this desktop R function, deploy it to an Oracle Database, and make it work at real-world scale.  The first step we did was to get some sample data.  For a historical IRR calculation, you have a balances and cash flows.  In our case, the customer provided us with several accounts worth of sample data in Microsoft Excel.      The above figure shows part of the spreadsheet of sample data.  The data provides balances and cash flows for a sample account (BMV=beginning market value. FLOW=cash flow in/out of account. EMV=ending market value). Once we had the sample spreadsheet, the next step we did was to read the Excel data into R.  This is something that R does well.  R offers multiple ways to work with spreadsheet data.  For instance, one could save the spreadsheet as a .csv file.  In our case, the customer provided a spreadsheet file containing multiple sheets where each sheet provided data for a different sample account.  To handle this easily, we took advantage of the RODBC package which allowed us to read the Excel data sheet-by-sheet without having to create individual .csv files.  We wrote ourselves a little helper function called getsheet() around the RODBC package.  Then we loaded all of the sample accounts into a data.frame called SimpleMWRRData. Writing the IRR function At this point, it was time to write the money weighted rate of return (MWRR) function itself.  The definition of MWRR is easily found on the internet or if you are old school you can look in an investment performance text book.  In the customer proof, we based our calculations off the ones defined in the The Handbook of Investment Performance: A User’s Guide by David Spaulding since this is the reference book used by the customer.  (One of the nice things we found during the course of this proof-of-concept is that by using R to write our IRR functions we could easily incorporate the specific variations and business rules of the customer into the calculation.) The key thing with calculating IRR is the need to solve a complex equation with a numerical approximation technique.  For IRR, you need to find the value of the rate of return (r) that sets the Net Present Value of all the flows in and out of the account to zero.  With R, we solve this by defining our NPV function: where bmv is the beginning market value, cf is a vector of cash flows, t is a vector of time (relative to the beginning), emv is the ending market value, and tend is the ending time. Since solving for r is a one-dimensional optimization problem, we decided to take advantage of R’s optimize method (http://stat.ethz.ch/R-manual/R-patched/library/stats/html/optimize.html). The optimize method can be used to find a minimum or maximum; to find the value of r where our npv function is closest to zero, we wrapped our npv function inside the abs function and asked optimize to find the minimum.  Here is an example of using optimize: where low and high are scalars that indicate the range to search for an answer.   To test this out, we need to set values for bmv, cf, t, emv, tend, low, and high.  We will set low and high to some reasonable defaults. For example, this account had a negative 2.2% money weighted rate of return. Enhancing and Packaging the IRR function With numerical approximation methods like optimize, sometimes you will not be able to find an answer with your initial set of inputs.  To account for this, our approach was to first try to find an answer for r within a narrow range, then if we did not find an answer, try calling optimize() again with a broader range.  See the R help page on optimize()  for more details about the search range and its algorithm. At this point, we can now write a simplified version of our MWRR function.  (Our real-world version is  more sophisticated in that it calculates rate of returns for 5 different time periods [since inception, last quarter, year-to-date, last year, year before last year] in a single invocation.  In our actual customer proof, we also defined time-weighted rate of return calculations.  The beauty of R is that it was very easy to add these enhancements and additional calculations to our IRR package.)To simplify code deployment, we then created a new package of our IRR functions and sample data.  For this blog post, we only need to include our SimpleMWRR function and our SimpleMWRRData sample data.  We created the shell of the package by calling: To turn this package skeleton into something usable, at a minimum you need to edit the SimpleMWRR.Rd and SimpleMWRRData.Rd files in the \man subdirectory.  In those files, you need to at least provide a value for the “title” section. Once that is done, you can change directory to the IRR directory and type at the command-line: The myIRR package for this blog post (which has both SimpleMWRR source and SimpleMWRRData sample data) is downloadable from here: myIRR package Testing the myIRR package Here is an example of testing our IRR function once it was converted to an installable package: Calculating IRR for All the Accounts So far, we have shown how to calculate IRR for a single account.  The real-world issue is how do you calculate IRR for all of the accounts?This is the kind of situation where we can leverage the “Split-Apply-Combine” approach (see http://www.cscs.umich.edu/~crshalizi/weblog/815.html).  Given that our sample data can fit in memory, one easy approach is to use R’s “by” function.  (Other approaches to Split-Apply-Combine such as plyr can also be used.  See http://4dpiecharts.com/2011/12/16/a-quick-primer-on-split-apply-combine-problems/). Here is an example showing the use of “by” to calculate the money weighted rate of return for each account in our sample data set.  Recap and Next Steps At this point, you’ve seen the power of R being used to calculate IRR.  There were several good things: R could easily work with the spreadsheets of sample data we were given R’s optimize() function provided a nice way to solve for IRR- it was both fast and allowed us to avoid having to code our own iterative approximation algorithm R was a convenient language to express the customer-specific variations, business-rules, and exceptions that often occur in real-world calculations- these could be easily added to our IRR functions The Split-Apply-Combine technique can be used to perform calculations of IRR for multiple accounts at once. However, there are several challenges yet to be conquered at this point in our story: The actual data that needs to be used lives in a database, not in a spreadsheet The actual data is much, much bigger- too big to fit into the normal R memory space and too big to want to move across the network The overall process needs to run fast- much faster than a single processor The actual data needs to be kept secured- another reason to not want to move it from the database and across the network And the process of calculating the IRR needs to be integrated together with other database ETL activities, so that IRR’s can be calculated as part of the data warehouse refresh processes In our next blog post in this series, we will show you how Oracle R Enterprise solved these challenges.

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