We define the vector variable

zt=(P1,t, P2,t, P3,t, MA1,t, MA2,t, MA1,t, Ftfund, Ftma)'.
In the following we denote the dynamical system by Φ, where
zt=Φ(zt-1).
Additive dynamic noise can be introduced into the system to obtain
zt=Φ(zt-1) + εt,
where εt=(εt, 0,0,0,0,0,0,0)' are iid random variables representing the model approximation error in that our model can only be an approximation of the real world. Because we assumed for all beliefs
Vth(rt+1P)=Vth


Pt+1+Dt+1-Pt
Pt



2
and because Pt+1 and Dt+1 are independent, this implies
Vth(Pt+1)=Pt2 σ2 - Vth(Dt+1)=Pt2 σ2 - σδ2.
Therefore, when we add dynamic noise to the deterministic skeleton, we draw εt iid from a normal distribution with expectation 0 and variance
σεt2=Pt2 σ2 - σδ2.

6.4  Trading volume

In this section we describe a procedure to determine trading volume. The total number of short or long positions transferred from belief b to belief h at time t converges in probability to zt-1b qth as the number of agents, each having zero market power, converges to infinity. The total number of long and short positions transferred to belief h from the other beliefs converges then in probability to
#longt(→ h)
p
 
H
b=1
zt-1b qth I(zt-1b ≥ 0);
#shortt(→ h)
p
 
|
H
b=1
zt-1b qth I(zt-1b<0) |,
    (40)
where I(.) is the indicator function. The demand for shares of each belief, under the equilibrium price which is set by the auctioneer, is equal to
zth=
yth Wth
Pt
p
 
yth qth Wt
Pt
.
257