c1a44fd2a6
Add README.md files for moeo/tutorial/Lesson{1-4}, smp/tutorial/Lesson{1-4},
and mo/tutorial/Lesson9 — these tutorials had no documentation.
Fix return 1 → return 0 in 28 tutorial main() functions across mo/ and
smp/ that unconditionally returned failure status.
84 lines
1.9 KiB
Markdown
84 lines
1.9 KiB
Markdown
# How to run your first multi-objective EA?
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In this lesson you will solve the Schaffer SCH1 bi-objective problem with
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NSGA-II using the ParadisEO-MOEO framework.
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The SCH1 problem minimizes two objectives over a single real-valued
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variable x in [0, 2]:
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- f1(x) = x^2
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- f2(x) = (x - 2)^2
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## 1. Running
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From the `build/moeo/tutorial/Lesson1` directory:
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```shell
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./Sch1 --help
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./Sch1 --popSize=100 --maxGen=100
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```
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Parameters can also be read from a file:
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```shell
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./Sch1 @Sch1.param
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```
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## 2. Browsing the code
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Open `Sch1.cpp` and follow along.
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First, define the objective vector traits. This tells MOEO how many
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objectives the problem has and whether each is minimizing or maximizing:
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```c++
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class Sch1ObjectiveVectorTraits : public moeoObjectiveVectorTraits
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{
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public:
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static bool minimizing (int) { return true; }
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static bool maximizing (int) { return false; }
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static unsigned int nObjectives () { return 2; }
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};
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```
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The solution class `Sch1` inherits from `moeoRealVector` — a real-valued
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decision vector that also carries an objective vector:
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```c++
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class Sch1 : public moeoRealVector < Sch1ObjectiveVector >
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{
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public:
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Sch1() : moeoRealVector < Sch1ObjectiveVector > (1) {}
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};
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```
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The evaluator computes both objectives and stores them via
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`objectiveVector()`:
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```c++
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void operator () (Sch1 & _sch1)
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{
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if (_sch1.invalidObjectiveVector()) {
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Sch1ObjectiveVector objVec;
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double x = _sch1[0];
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objVec[0] = x * x;
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objVec[1] = (x - 2.0) * (x - 2.0);
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_sch1.objectiveVector(objVec);
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}
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}
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```
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The algorithm itself is a single line — `moeoNSGAII` takes the generation
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limit, evaluator, crossover, and mutation as constructor arguments:
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```c++
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moeoNSGAII < Sch1 > nsgaII (MAX_GEN, eval, xover, P_CROSS, mutation, P_MUT);
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```
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After the run, extract the Pareto front with `moeoUnboundedArchive`:
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```c++
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moeoUnboundedArchive < Sch1 > arch;
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arch(pop);
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arch.sortedPrintOn(cout);
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```
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