C vs javascript
The difference between standard C compiled GLPK and the Javascript version seems to be a factor 10. As one could expect the solution path is slightly different. C based glpsol.exeGLPK Simplex...
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Loading large data set into GAMS GDX file
For a project we convert data from a humongous table with 23 million records stored in a remote SQL Server database (global spatial grid with data on agricultural production and land use from the...
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Book: Complementarity Modeling in Energy Markets
http://www.amazon.com/Complementarity-Modeling-International-Operations-Management/dp/1441961224Looks interesting.
View ArticleExcel 1 million row limit
Excel 7 (and later) has limit of 1,048,576 rows (before version 7 this limit was 65,536 rows). When using COM automation (using Excel from a program) one usually turns off DisplayAlerts to prevent...
View ArticleGAMS/GDX cannot read scalar from compressed GDX file
I encountered a problem when reading a scalar from a compressed GDX file:GDXIN C:\projects\ulrike - ifpri\gdx\spam.gdx --- LOAD cell5m = 2:cell5m --- LOAD rowcount = 1:rowcount **** Problem reading...
View ArticleGAMS sameas problem
I tried a construct that looks like the following code:sets cell5m cell5m_spam ; $gdxin d.gdx $load cell5m cell5m_spamset cellmap(cell5m,cell5m_spam);...
View ArticleSQL Server and PIVOT/UNPIVOT
http://msdn.microsoft.com/en-us/library/ms177410(v=sql.105).aspxI think the syntax is somewhat confusing, but this thing can be handy. Not all databases I encounter are normalized! In fact I see many...
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GAMS/VBScript Tool to view DBF table structure
When receiving DBF files I usually look at the structure by loading it into Excel. In this case I received DBF files that were much too large to be handled by Excel. Before writing queries it is useful...
View ArticleGAMS to OpenOpt too scary?
http://forum.openopt.org/viewtopic.php?id=579:“This works though I'm worried it might look too scary to my students coming from GAMS.”
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Errmsg
After installing GAMS one of the first things to do is to change one of its more obscure options:Without this you get the convenient default where error messages are not shown where the errors are....
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GAMS Plotting Marginals
The GAMS/IDE has an issue plotting marginals. When we select the marginals of an equation, and try to plot these, we actually get the levels:The workaround is to create an extra parameter and assign to...
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option optcr?
In the following paper an MIQP formulation is proposed for an optimal dispatch problem for power generators where some of the generators have certain output levels that are not allowed. Often we see...
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big-M
In http://bob4er.blogspot.com/2013/02/the-big-m.html a big-M constraint (my favorite subject!) is formed like:xij≤ [1.1 min (ai, bj)] zijI don’t really understand the reason for the fudge factor 1.1. I...
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Meta-Heuristics or Math Programming
The problem of scheduling maintenance of generators is a well-studied problem. In particular a specific data sets has been used a lot: all use the same problem. They all use some form of...
View ArticleSQL and NULL
Yesterday this came up again: a client was using a query with something like:SELECT xxx FROM yyy WHERE zzz=NULLThis does not work as expected. This query will always return zero rows. The correct way...
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SOS2 in GAMS
https://groups.google.com/d/topic/gurobi/YZGRWaA-oQE/discussion:No, sorry, this is not at all the case. In the link...
View ArticleRepeating messages
Solvers sometimes spit out messages that are basically similar. Here is an example of a list of a few million messages (literally!):MOSEK Warning 53 : A numerically large upper bound value 2.3e+009...
View ArticleOption optcr
For MIQCPs Mosek seems to ignore the relative gap provided by GAMS (option optcr). With either option opctr=0.1 (default) or optcr=0 (solve to optimality) I see:An optimal solution satisfying the...
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