GAMS Python API documentation version 24.1

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18 Class Documentation In the GAMS Python API we map the IEEE standard values for +/-infinity (float(’inf’)/float(’-inf’)) and NA (float(’nan’)) to the corresponding GAMS values. The special value for UNDEF gets unfiltered through the GAMS Python API. The internal double value of UNDEF is 1.0E300 (or better use the constant SV_UNDEF). Special attention needs to be given to the value of 0. Since GAMS is a sparse system it does not store (parameter) records with a true 0. If a record with numerical value of 0 is needed, EPS(SV_EPS) can help. For example: set j /1*10 /; parameter b(j); b(j) = 1; b(’5’) = 0; scalar s,c; s = sum(j, b(j)); c = card(b); display s,c; will result in ---- 3 PARAMETER s = 9.000 PARAMETER c = 9.000 but b(j) = 1; b(’5’) = EPS; will result in ---- 3 PARAMETER s = 9.000 PARAMETER c = 10.000 What are the consequences for the GAMS Python API? If we read parameter b in case of b(’5’)=0, the GAM- SDatabase will not have a record for b(’5’). In case of b(’5’)=EPS, the GamsDatabase will have a record with value EPS. Unlike the IEEE values (e.g. float("inf")), arithmetic operations in Python will modify EPS (e.g. 5∗E- PS==float("inf") but 5∗EPS!=EPS). The same rules apply for preparing input data for GAMS in a GamsDatabase. If a value of EPS is written, GAMS will see the special value EPS. All other small values (including 0) will be communicated unfiltered to GAMS. As mentioned before, zeros will not be entered as data records in GAMS. The compiler control $on/offEPS can help to automatically map zeros to EPS. There is one oddity concerning values smaller than 1e-250 on GAMS input. Consider the following example: 1 b = db.add_parameter("b",1) 2 for i in range(1,11): 3 b.add_record(str(i)).value = 1 4 b.find_record("5").value = 1E-251 5 job.run(db) $load j b scalar card_b; card_b = card(b); display card_b; b(j) = 2*b(j); card_b = card(b); display card_b; A record with values smaller than 1e-250 exists on input in GAMS, but as soon as the record gets updated by GAMS and is still smaller than 1e-250, the record gets removed. The ordering of a set in GAMS can be non-intuitive: Consider "set i /5/, j /1∗5/;". Elements ’5’ gets internal number 1, ’1’ get 2, ’2’ gets 3 and so on. The last element of j ’5’ has already the internal number 1. The sequence of internal numbers in j is not ascending and hence GAMS considers set j as not sorted, i.e. one can’t use the ord() function nor the lag or lead (-,–,+,++) operators. If ’j’ would have been defined before ’i’ in this example, the "set not ordered" problem would have been avoided. Please note that the GamsDatabase actually does not implement a relational model for database management. It should be seen as a data storage or data container. 4.3.2 Member Function Documentation 4.3.2.1 def gams.database.GamsDatabase.add equation ( self, identifier, dimension, equtype, explanatory text = "" ) Add equation symbol to database. GAMSPythonAPI documentation version 24.1 May 2013
4.3 gams.database.GamsDatabase Class Reference 19 Parameters identifier Equation name dimension Equation dimension equtype Equation subtype (EquType.E: Equal, EquType.G: Greater, EquType.L: Less, EquType.N: No specification, EquType.X: External defined, EquType.C: Conic) explanatory_text Explanatory text of equation See Also add_parameter(), add_set(), add_variable() 4.3.2.2 def gams.database.GamsDatabase.add equation dc ( self, identifier, equtype, domains, explanatory text = "" ) Add equation symbol to database using domain information. Parameters identifier Equation name equtype Equation subtype (EquType.E: Equal, EquType.G: Greater, EquType.L: Less, EquType.N: No specification, EquType.X: External defined, EquType.C: Conic) domains A list containing GamsSet objects and strings for domain information. The length of the list specifies the dimension. explanatory_text Explanatory text of equation See Also add_parameter_dc(), add_set_dc(), add_variable_dc() 4.3.2.3 def gams.database.GamsDatabase.add parameter ( self, identifier, dimension, explanatory text = "" ) Add parameter symbol to database. Parameters identifier Parameter name dimension Parameter dimension explanatory_text Explanatory text of parameter See Also add_equation(), add_set(), add_variable() 4.3.2.4 def gams.database.GamsDatabase.add parameter dc ( self, identifier, domains, explanatory text = "" ) Add parameter symbol to database using domain information. Parameters identifier Parameter name domains A list containing GamsSet objects and strings for domain information. The length of the list specifies the dimension. explanatory_text Explanatory text of parameter GAMSPythonAPI documentation version 24.1 May 2013
Page 1: GAMS Python API documentation versi
Page 4 and 5: ii CONTENTS 4.3.1 Detailed Descript
Page 6 and 7: iv CONTENTS 4.22.1 Detailed Descrip
Page 8 and 9: vi CONTENTS 4.51.1 Detailed Descrip
Page 10 and 11: 2 GAMS Python API export PYTHONPATH
Page 12 and 13: 4 GAMS Python API GAMSPythonAPI doc
Page 14 and 15: 6 Hierarchical Index gams.options.S
Page 16 and 17: 8 Class Index gams.execution.Symbol
Page 18 and 19: 10 Class Index GAMSPythonAPI docume
Page 20 and 21: 12 Class Documentation Properties
Page 22 and 23: 14 Class Documentation 4.1.2.8 def
Page 24 and 25: 16 Class Documentation Get GamsEqua
Page 28 and 29: 20 Class Documentation See Also add
Page 30 and 31: 22 Class Documentation Parameters R
Page 34 and 35: 26 Class Documentation 4.8 gams.dat
Page 36 and 37: 28 Class Documentation 4.12 gams.da
Page 38 and 39: 30 Class Documentation 4.14.2 Const
Page 40 and 41: 32 Class Documentation Parameters g
Page 42 and 43: 34 Class Documentation 17 for rec i
Page 44 and 45: 36 Class Documentation 4.18 gams.ex
Page 46 and 47: 38 Class Documentation 4.20.1 Detai
Page 48 and 49: 40 Class Documentation • int Dot
Page 52 and 53: 44 Class Documentation • bratio p
Page 54 and 55: 46 Class Documentation 4.29 gams.op
Page 56 and 57: 48 Class Documentation Inheritance
Page 58 and 59: 50 Class Documentation 4.37 gams.op
Page 60 and 61: 52 Class Documentation 4.40.1 Detai
Page 62 and 63: 54 Class Documentation 4.45 gams.wo
Page 64 and 65: 56 Class Documentation There was a
Page 66 and 67: 58 Class Documentation • major_re
Page 68 and 69: 60 Class Documentation Returns Gams
Page 70 and 71: 62 Class Documentation Parameters m
Page 72 and 73: 64 Class Documentation • int Capa
Page 74 and 75: Index __init__ gams::execution::Gam
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68 INDEX gams::database::GamsDataba
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