Under control: managing errors and warnings within AIMMS

molumen_Exclamation_icons_1The goal of this article is to explain how you can control errors and warnings within AIMMS. Namely, we will walk you through some useful tips that can help you manage errors and warnings in the best possible way to create better models.

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Professionally Operating Your AIMMS PRO Platform

best practices

AIMMS started life as a desktop product. Users were mostly individually responsible for looking after their applications, managing the changes, making back-ups, etc. Unwanted incidents such as bugs, accidental project deletion and hardware failures usually had a very limited local impact. Of course mission-critical AIMMS applications were already managed more rigorously.

The advent of AIMMS PRO is introducing new application management challenges as many more users and/or business operations potentially depend on a single PRO platform for performing their tasks. We see our clients looking for ways to professionally operating their PRO platforms. Purpose of this blog post is to provide you with some aspects to consider in this context. We are not proposing anything novel, but merely pointing out some common practices of application management. Continue reading »

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Installing 32-bit and 64-bit Microsoft Access Drivers next to each other

32_bit_vs_64_bitSome years ago, before Microsoft Office 2010, life was – in some sense – easier for developers: Office was 32-bit, period. In our days, since the release of Microsoft Office 2010, things are a bit more complicated, as users can now have a machine with a 64-bit native version of Office installed as well. This means, for instance, that a 32-bit application using an ODBC driver to connect to an Access database might not work anymore, since the 32-bit ODBC driver might not exist on a machine with a 64-bit Office installation. In such a case, even though the user has a valid Office installation on his or her machine, the application may still display an error regarding the installation or the registration of the proper drivers on the local machine. Continue reading »

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Investigating infeasible nonlinear problems

sherlockThe AIMMS webinar of August (2014) dealt with “Analyzing infeasible Problems in AIMMS”. In case you missed it, the recording can be found here. As shown in the webinar, one way to investigate an infeasible problem is by calculating an Irreducibly Inconsistent System (IIS). An IIS is a subset of all constraints and variables that contains an infeasibility. The “Irreducibly” part implies that the subset is as small as possible. Unfortunately, the IIS could only be calculated for linear (and quadratic) problems. So how about nonlinear problems?

AIMMS 4.1 introduces version 14 of BARON. BARON is a solver for solving non-convex optimization problems to global optimality. Version 14 can calculate an IIS for infeasible nonlinear problems including problems with integer variables. To let BARON calculate an IIS, the option Compute IIS should be switched on. BARON offers several algorithms for calculating an IIS, the fastest being a heuristic that “only” calculates an IS (as the infeasible system found could possibly be reduced further). BARON 14 also brings significant improvements in the handling of integer problems. Note that finding a global optimum takes more time than finding a local optimum like most nonlinear solvers do.

Another way to analyze an infeasible problem is by using the Display Infeasibility Analysis option of the AIMMS presolver. This also prints an infeasible set of constraints and variables. In previous versions of AIMMS this set could contain superfluous constraints and variables, but AIMMS 4.1 uses an algorithm to calculate an (almost) irreducible set. Note that the AIMMS presolver cannot always detect that an infeasible problem is indeed infeasible.

Both the Infeasibility Analysis and the IIS, as calculated by BARON, are printed in the listing file.

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AIMMS 4: model sources, version control and aimmspack files

keep_calm_and_carry_on_coasters-r44b83d095b374e2d9454dc9b102fab13_am0u7_8byvr_152In our current AIMMS 4.0 release we have introduced a number of fundamental, and sometimes breaking changes in managing the project sources, about which we got a lot of questions. In this blog post, I will describe these changes and also explain the rationale behind them.

Binary versus text-only source files

In AIMMS 3, all project sources were stored in a binary format. Originally, we introduced these binary files in AIMMS 3 to reduce the total number of files associated with a project. However, over time it turned out that a major drawback of this approach was that the binary format made it very hard to effectively collaborate on an AIMMS 3 project, because the binary files make it really cumbersome to combine the changes made by multiple developers into a new version of the project. For many years, our larger customers have asked us to address this problem, and we partially mitigated it by introducing libraries in AIMMS 3. This allowed multiple developers to work on separate libraries, thus facilitating a limited form of collaboration. Continue reading »

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Formulas as Data

mathematics-327488_150A mathematical formula is considered data within an application when it is read in as a string during the application’s runtime, and subsequently used in the construction of selected assignments and constraints. The concept “Formulas as Data” can be applied to several optimization apps, for instance those that deal with “Blending on Specification” and “Asset Management.” In these types of applications, the benefit of the end-users is that they do not have to share these formulas with anyone else, including the developers of the apps. For such apps, good formulas are expensive to develop and having good formulas provides a competitive edge to these end-users. In AIMMS, formulas can be used in the following way:

  • String parameters – a formula is a sequence of characters, and such sequences can be stored and manipulated via string parameters. Such manipulation is executed at AIMMS run time.
  • Macros – a formula is a mathematical expression and this expression is created during AIMMS compilation time.

The two identifier types, string parameter and macro, effective at different times as far as the AIMMS system is concerned, need to be combined in order to support the concept “Formulas as Data.” How do we go about this? Continue reading »

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Repetitive Patterns captured by Model Query and Model Edit Functions

Der Maler - Honoré Daumier - from Rheims Museum of Fine Arts

Der Maler – Honoré Daumier – from Rheims Museum of Fine Arts

When constructing AIMMS models, we are usually able to handle repetition and structure by adding indexes. For instance, if we have built a model for the conversion process of a single machine, we do not have to duplicate the relevant model code when given an extra machine. Instead, we can use an extra index over a set of machines. However, there are situations where adding an extra index is not an option. This blog post will provide an example of such a situation, illustrating how the issue can be tackled using the AIMMS Model Query and Model Edit functions. Continue reading »

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Modeling the forest: Ontario’s Ministry of Natural Resources takes us through decades of effective forest management

SCI_MNR_logo_bronzeForest ecosystems are highly complex and influenced by a diversity of factors. Sustainable forest management is therefore an ongoing and constantly evolving process which requires an integrated approach. Government bodies, such as The Ontario Ministry of Natural Resources (OMNR), must conform to provincial policies and standards, while taking economical and ecological considerations into account to arrive at optimal forest management policies. OMNR manages 27 million ha of Ontario’s public forest and has been using an AIMMS-based model for this purpose since 1994. The Strategic Forest Management Model, or SFMM, enables foresters to analyze the relationships between forest condition, silvicultural practices, wood supply and potential wildlife habitat. This analysis enables them to understand how a forest develops through time and explore alternative forest management strategies and trade-offs. Today, nearly 2 decades after its launch, we spoke with Dirk Kloss, OMNR’s Resource Modeling Specialist, to find out where SFMM stands today and what their experience using AIMMS has been like.

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Using external functions for data input

Make connection

Make connection

Data exchange is an essential part of every application. AIMMS supports various industry standards for data exchange, such as ODBC for databases, XML Files and spreadsheets. But what if the data is not stored according to one of these standards? In order to read data from an arbitrary data source, AIMMS offers access to self-developed or third party functions. This blog post provides an overview of the steps you need to take to create a data exchange link between a proprietary data format and AIMMS. The process is illustrated by using a concrete modeling exercise from the Constraint Programming example library CSPLIB. Continue reading »

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Monitoring memory use

Memory module

Memory module

Analytic applications may involve a lot of data and subsequently a lot of computer memory. AIMMS hides the technicalities related to memory management from the model developer. These technicalities include, for instance, the allocation and deallocation of memory for individual data items. Still, the memory usage of applications created with AIMMS grows as the amount of data related to these applications grows. At some point during model development, the memory usage of your application becomes interesting. AIMMS offers tools to monitor and investigate the memory usage of your application. This blog post will delve into some of these tools. Continue reading »

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