Code snippets for page Growing Neural Gas

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# -*- coding: utf-8 -*-
# Generated by codesnippet sphinx extension on 2016-03-08

import mdp
import numpy as np
np.random.seed(0)
mdp.numx_rand.seed(1266090063)

def uniform(min_, max_, dims):
    """Return a random number between min_ and max_ ."""
    return mdp.numx_rand.random(dims)*(max_-min_)+min_
def circumference_distr(center, radius, n):
    """Return n random points uniformly distributed on a circumference."""
    phi = uniform(0, 2*mdp.numx.pi, (n,1))
    x = radius*mdp.numx.cos(phi)+center[0]
    y = radius*mdp.numx.sin(phi)+center[1]
    return mdp.numx.concatenate((x,y), axis=1)
def circle_distr(center, radius, n):
    """Return n random points uniformly distributed on a circle."""
    phi = uniform(0, 2*mdp.numx.pi, (n,1))
    sqrt_r = mdp.numx.sqrt(uniform(0, radius*radius, (n,1)))
    x = sqrt_r*mdp.numx.cos(phi)+center[0]
    y = sqrt_r*mdp.numx.sin(phi)+center[1]
    return mdp.numx.concatenate((x,y), axis=1)
def rectangle_distr(center, w, h, n):
    """Return n random points uniformly distributed on a rectangle."""
    x = uniform(-w/2., w/2., (n,1))+center[0]
    y = uniform(-h/2., h/2., (n,1))+center[1]
    return mdp.numx.concatenate((x,y), axis=1)
N = 2000

cf1 = circumference_distr([6,-0.5], 2, N)
cf2 = circumference_distr([3,-2], 0.3, N)

cl1 = circle_distr([-5,3], 0.5, N/2)
cl2 = circle_distr([3.5,2.5], 0.7, N)

r1 = rectangle_distr([-1.5,0], 1, 4, N)
r2 = rectangle_distr([+1.5,0], 1, 4, N)
r3 = rectangle_distr([0,+1.5], 2, 1, N/2)
r4 = rectangle_distr([0,-1.5], 2, 1, N/2)

x = mdp.numx.concatenate([cf1, cf2, cl1, cl2, r1,r2,r3,r4], axis=0)
x = mdp.numx.take(x,mdp.numx_rand.permutation(x.shape[0]), axis=0)

gng = mdp.nodes.GrowingNeuralGasNode(max_nodes=75)

STEP = 500
for i in range(0,x.shape[0],STEP):
    gng.train(x[i:i+STEP])
    # [...] plotting instructions
gng.stop_training()

n_obj = len(gng.graph.connected_components())
print n_obj
# Expected:
## 5