The changes in this beta will be available in the upcoming 4.9.0 production release that will be out in June.
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 out the issue and fixed it!
Technical 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 0.09% 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. The functions are not implemented directly within the Microsoft .NET framework, instead, they are implemented in the Microsoft C run-time libraries which are used by the .NET framework, as well as by a number of other languages including C++. So the nature of the .NET framework, which is an interpreted language, wasn’t part of the issue and the same results would have been obtained if implemented in C++. 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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