What does it mean to supply a "partial" initial population to "gaoptimset" in the Global Optimization Toolbox (R2010a and later)?

I am using the genetic algorithm "ga" to perform an optimization and configuring the options for the optimization with "gaoptimset" .  I noticed in the documentation that the 'InitialPopulation' I provide may be "partial".  However, I am not sure what this means, and the documentation for "gaoptimset" is not clear.  What is a "partial" initial population?

Answer 1

[MathWorks Support Team]

The documentation for "gaoptimset" does not explicitly state what a "partial" initial population is:  

 

InitialPopulationInitial population used to seed the genetic algorithm; can be partialMatrix | {[]}

However, the larger documentation page titled "Genetic Algorithm Options" provides more insight:

Initial population

('InitialPopulation') specifies an initial population for the genetic algorithm. The default value is [], in which case ga uses the default

Creation function

to create an initial population. If you enter a nonempty array in the

Initial population

field, the array must have no more than

Population size

rows, and exactly

Number of variables

columns. In this case, the genetic algorithm calls a

Creation function

to generate the remaining individuals, if required.

Therefore, a "partial" initial population simply refers to an initial population with fewer individuals than the specified (or default) population size.  As an example, compare the population sizes of the initial and final populations in the following example:

rf2 = @(x)rastriginsfcn(x/10); % objective function
x0 = [20,30]; % starting point away from the minimum
initpop = 10*randn(20,2) + repmat([10 30],20,1); % generate an initial population

% specify a larger population than the size of the initial population
opts = gaoptimset('PopulationSize', 100, 'InitialPopulation',initpop);

% run the optimization
[xga fga flga oga,pop] = ga(rf2,2,[],[],[],[],[],[],[],opts);

The initial population "initpop" consists of only 20 individuals, but the specified 'PopulationSize' (and the number of rows in the final population "pop") is 100 individuals.