2 computers x 1 model = 2 different results = ####
This has been a major problem for a small (but important!) group of Source users.
eWater is pleased to announce we’ve worked it out the issue and fixed it!
Details:
Source uses the Microsoft .net framework, the problem was caused by 2 functions in the System.Math library. Both System.Math.Pow() and System.Math.Exp() can give different results for some number combinations on different machines. For individual function calls, different results occurred at <Kuan<Kuan:> % of the time with our randomly generated test data. We believe the issue is from different CPU’s implementing different optimisations to perform the operations as efficiently as possible. Within the Microsoft .net framework they are implemented as C++ operations, so the nature of the .net framework which is an interpreted language wasn’t part of the issue. We have since tested all available System.Math functions and these are the only two we have found that can produce different results on different machines. The vast majority of models don’t see the issue since the differences are very minor and for an individual operation, the difference is only at the last decimal place. However, for very large models with lots of feedback in the model, when the issue occurs it can snowball into meaningful result differences.
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We have approached Microsoft about the issue and they are yet to respond.
<Kuan<Kuan: can you add in the link for the Microsoft post and include details about where the library currently is for plugin developers>
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