Data Analysis & Simulation

EasyFitXL - the distribution fitting add-in for Excel - was first introduced with the release of EasyFit 4.0 back in 2007. When designing EasyFitXL, we did a lot of research as to which Excel versions to support. At that time, the latest version of Excel was Excel 2007, which included some new useful features, such as the support for larger worksheets and multi-threaded worksheet recalculation capability. However, many customers were not rushing to upgrade to Excel 2007 because of it’s controversial Ribbon Interface, so we had to make EasyFitXL compatible with the previous version - Excel 2003.

According to some publicly available data, Excel 2002 and Excel 2000 still had a considerable user base, so we have made a decision to support these two older versions as well. As a result, EasyFitXL initially included support for Excel versions from 2000 through 2007, covering perhaps over 99% of all Excel installations in the world.

Last month Microsoft has released Excel 2010 which does not make a big difference in terms of data analysis, however, with its release we started receiving compatibility complaints from our customers, so we performed an in-depth testing and released an updated version of EasyFit (available for download).

Recently a customer has contacted us and noted that the Inverse Cumulative Distribution Function (the Quantile Function) of the Inverse Gaussian distribution implemented in EasyFit works well for lambda=1902.1, mu=41857.0 and P=0.9, but fails for the same lambda & mu and P=0.99. Last week we have released an updated version of EasyFit that fixes the problem, and in this post we would like to elaborate more on the issue.

Evaluating the Inverse CDF of the Inverse Gaussian Model
Since the CDF of the Inverse Gaussian distribution is quite complicated (expressed in terms of the two Laplace Integrals), the Inverse CDF of this model is not available in closed form, and cannot be easily evaluated for a given set of distribution parameters. Initially, we have implemented an iterative approximation algorithm that evaluates the ICDF(P) using the CDF as well as the PDF to speed up the calculation. The algorithm itself works very well over a great range of input parameters, however, we have placed a limitation on how many iterations it is allowed to perform.

Because EasyFit is considered an interactive data analysis tool, we are always looking for a balance between the feature set and the performance, which is especially important when using EasyFit with Excel worksheets calculated in real time. The limitation on the number of iterations is necessary to make sure the algorithm doesn’t fall into an “infinite loop”, meaning the situation when it’s unable to reach the specified accuracy regardless of how long it continues to work. The problem usually happens when we are hitting the precision limitations of the computer’s CPU: in theory, the algorithm must converge in a limited number of steps, but in reality, it will just continue iterating over and over again without any accuracy improvements.

As a solution, we have made some improvements to the algorithm, making it more robust and efficient, so it now works with the same accuracy, but for a larger range of input parameters. For example, considering the parameters that initially caused the problem (lambda=1902.1 and mu=41857.0), the ICDF(P) can be evaluated for values of P up to 0.999925, which is more than enough for most statistical analysis applications.

Should You Upgrade?
Since this minor issue does not affect the accuracy of distribution fitting, you only need to upgrade if you are experiencing problems evaluating the Inverse CDF of the Inverse Gaussian distribution for P>0.9, otherwise EasyFit 5.2 will still work well for you.

The new Software Development Kit enabling you to easily add Monte Carlo simulation and distribution analysis features to your applications is now available for public beta testing - please download the free beta version and take a look at the code examples (available in several languages, including C#, VB.NET, C++, and Visual Basic for Applications).

We would be glad to receive any feedback, questions or suggestions from you, so please feel free to drop us a line and let us know what you think about this product and how we can make it better.

Earlier in December 2008, we announced our plans to create the Software Development Kit that would allow software developers to integrate the simulation and probabilistic analysis functionality of EasyFit into their custom software solutions. Since then, we have been working hard to bring the SDK to market. Despite some delays, we are glad to announce that we have successfully completed the development, and this month we plan to release the beta version of the product.

Become a Beta Tester Today!
Taking part in our beta testing program would not just grant you access to the cutting edge software technology - the most active beta testers will also be able to purchase the SDK at an introductory price before the production version of the SDK is released. To sign up, please contact us with your specific requirements (let us know how you plan to use the SDK and what development platform (C#, VB.NET etc.) you are using.)

We have just released EasyFit Version 5.1 - the update that fixes a bug causing an incorrect calculation of the chi-squared GOF statistic for small sample sizes. To upgrade, uninstall EasyFit 5.0 from your computer, then download and install the latest version.

Since fitting probability distributions to large data sets can be a time-consuming task, we are currently researching the possibility of using multi-core processors to make EasyFit work faster. During the past several years, major processor manufacturers have been promoting the multi-core technology on the desktop processors market. Multiple cores in a single chip allow for better performance/price ratio on a range of tasks, however, existing software needs to be updated accordingly to take full advantage of this type of hardware.

We have modified the original distribution fitting algorithm to utilize all cores available on a system, and used it to fit distributions to a simulated set of 200,000 data points. In a series of tests on an Intel dual-core processor, the new algorithm executed almost twice as fast, yielding up to 90% performance increase, compared to the version currently used in EasyFit. These are very good results, and we will definitely be including this feature into the next release of EasyFit.

On a related note, last week we were contacted by a customer regarding our upcoming Simulation & Probabilistic Analysis SDK. They need to analyze large volumes of data, and from their description of the problem we estimated that the typical analysis would take up to 20 hours on a modern PC. With the new distribution fitting algorithm, it can take less than 12 hours on a dual-core CPU, or even less on quad-core processors popular in the server space. In a decision making environment where several hours can mean the difference between profit and loss, this is a very important improvement.

Lately we have received a couple messages from customers asking if it’s possible to use the Monte Carlo simulation and distribution fitting features of EasyFit in their own software applications. The short answer is yes, but these features are limited to calculating some distribution functions in Excel VBA. There’s currently no way to run simulations, fit distributions to data, perform goodness of fit tests, or use distribution functions from C#, C++, VB.NET, and other programming languages.

To fill the gap, we are considering to create a Simulation & Probabilistic Analysis Software Development Kit (SPA SDK) for software developers who need to deal with risk & uncertainty in their applications, but don’t have time or expertise to design and implement the required features on their own. We already have in place the tried and true technology that’s a basis for our distribution fitting products EasyFit and EasyFitXL, so creating an SDK would be possible in a short period of time.

Since we have had only a few requests for an SDK, we would like to know whether you would be interested in such kind of product. Below is our vision for the SDK – you are welcome to express any thoughts or specific requirements you might have. Please feel free to contact us and we will take your input seriously.

Update: The free beta version of the SDK is now available for download - please click here for details.

What is a Simulation & Probabilistic Analysis Software Development Kit (SPA SDK) ? (more…)

EasyFit ships with a comprehensive help file providing detailed information on all aspects of fitting distributions to data and interpreting the analysis results. For instance, it includes the description of supported distributions, goodness of fit tests, and output graphs.

If you are considering to try EasyFit but not sure if it has a particular feature you need, you can refer to the EasyFit help online which we have made available on our website for your convenience. Of course, you are still welcome to contact us for any questions regarding EasyFit or fitting distributions in general.

From now on, our distribution fitting software EasyFit can be ordered on a CD, in addition to the download version. The motivation for adding this feature was that in some countries it is required for accounting purposes. Most times you won’t need a CD since EasyFit is available for immediate download from our website, but if you do need it, you might find this feature useful.

The CD will be produced exclusively for you, and will include the EasyFit installation package along with your personal license key and registration details in a separate file.

The CD is priced at $14.95, including shipping. To receive a CD, check the option “Order this product on a CD” and make sure you specify a valid postal address when filling in the order form. Once your order is processed, you will immediately receive your license key via email (so you can start using EasyFit right away), and the CD will be shipped to you in a few days.

We are glad to announce that customers from Italy can now purchase EasyFit, our distribution fitting software product, through SxST, the Milan-based company specializing in software solutions for science and technology.

SxST provides a wide range of scientific software products from recognized vendors to Italian businesses, government organizations and academic institutions. According to the agreement, SxST will be offering the Italian version of EasyFit and the first level support in Italian language to their clients, ensuring the best customer experience at the same cost as for the rest of EU countries.

It is really fascinating for us to see EasyFit standing in line with statistical software packages by Systat Software, Minitab, GraphPad, and StataCorp. Our partnership with SxST can be thought of as a milestone indicating that EasyFit has reached the quality level of brand name products offered by these long-established companies.