# Making Your Own Strategy : A Simple EDA¶

As seen in the Covariance Matrix Adaptation Evolution Strategy example, the
`eaGenerateUpdate()`

algorithm is suitable for algorithms
learning the problem distribution from the population. Here we’ll cover how to
implement a strategy that generates individuals based on an updated sampling
function learnt from the sampled population.

## Estimation of distribution¶

The basic concept concept behind EDA is to sample individuals
with a certain distribution and estimate the problem distribution from the
best individuals. This really simple concept adhere to the
generate-update logic. The strategy contains a random number generator which
is adapted from the population. The following `EDA`

class do just that.

A normal random number generator is initialized with a certain mean
(*centroid*) and standard deviation (*sigma*) for each
dimension. The `generate()`

method uses numpy to generate *lambda_*
sequences in *dim* dimensions, then the sequences are used to initialize
individuals of class given in the *ind_init* argument. Finally, the
`update()`

computes the average (centre) of the mu best individuals and
estimates the variance over all attributes of each individual. Once
`update()`

is called the distributions parameters are changed and a new
population can be generated.

## Objects Needed¶

Two classes are needed, a minimization fitness and a individual that will
combine the fitness and the real values. Moreover, we will use
`numpy.ndarray`

as base class for our individuals.

## Operators¶

The `eaGenerateUpdate()`

algorithm requires to set in a
toolbox an evaluation function, an generation method and an update method.
We will use the method of an initialized `EDA`

. For the generate
method, we set the class that the individuals are transferred in to our
`Individual`

class containing a fitness.

The complete examples/eda/fctmin.