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All Topics | Topic "Error Message: Failure to solve"
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Author Message
Ying Qiao

Subject: Error Message: Failure to solve   
Posted: 2/9/2011 Viewed: 21563 times
I constructed a WEAP model for a big basin. In this model there are 143 demand sites which have different priorities, 54 reservois (Lakes), 19 minimum flow requirements with priority 1 (highest), 61 river branches. The run period is for 11 years and time step is weekly, so the inputs are weekly values. When I ran the model, I got error message saying "Failure to solve in week13, year 1996. Results not available for this week and may not be accurate in later weeks.[Error Code = 2, ErrorNumber = 0, Error Message = 'Failed while solving allocation order 22, iteration 2, total iterations for this month 25 (Scenario: Current Accounts)']"

Anyone had seen this error before? and could anyone give suggestions on how to solve this error? what is the stop criteria (e.g. maximum number of iteration) in WEAP?

Your help is highly appreciated!

Jack Sieber

Subject: Re: Error Message: Failure to solve   
Posted: 2/9/2011 Viewed: 21562 times
I’m sorry for this problem. Had the model been running without errors before, or is this the first time you ran calculations? The error you see is a very rare one, involving the internal linear program (LP) solver finding an infeasibility. Theoretically, you should not be able to create an infeasible model. In practice, scaling issues and round off (due to the iterative nature of how WEAP solves the allocations for each timestep) can create an infeasibility. Most often this is caused by a scaling problem--very small values or very large values. Could you check the supply requirement (demand) in those timesteps to see if any are very large or very small? The allocation order referred to by the error message is the order in which WEAP performs allocations in each timestep. You can see the allocation order for each transmission link, reservoir and flow requirement on the schematic Main Menu: select Schematic, Change Priority View, Allocation order. Focus on the values for allocation order 22, either demand (demand sites and instream flow) or storage capacity (reservoir).
Topic "Error Message: Failure to solve"