@Override
    public float value(final float x, final float y, final float z) {
        return this.a.value(x, y, z) * (1 - this.rate) + this.rate * this.b.value(x, y, z);
    }
A simple aggregator basis. Takes two basis functions and a rate and return
some mixed values

@author Anthyon
jme3-terrain/src/main/java/com/jme3/terrain/noise/basis/NoiseAggregator.java