Re: [Pcsim-users] Gamma distribution and negative weights

[Mathieu D. <mat...@li...>]

Hello,

Mathieu Dubois wrote:
> Hello PCSIMers,
>
> I would like some advice on the best way to construct the reservoir of 
> an LSM.
>
> In the standard LSM literature, the weights of the intra-reservoir 
> synapses are drawn from a Gamma distribution with parameters depending 
> on the type of neurons connected (up to now I was using constant 
> weights but I would like to see if using those weights increase 
> performance).
> I have found the BndGammaDistribution object in PCSIM and the relevant 
> parameters in [1].
>
> The problem is: how can I generate negative weights within the liquid 
> (to connect an inhibitory neuron to another neuron)?
> The Gamma distribution returns positive numbers so I have to do this 
> by hand.
>
> I have looked into the (matlab) circuit toolbox and found the code:
> if synpar.W > 0
>   synpar.W = sign(synpar.W) * bnd_gammarnd(abs(synpar.W), sh(1), 
> abs(6*synpar.W), 1, m, 'exz A');
> else
>   synpar.W = sign(synpar.W) * bnd_gammarnd(abs(synpar.W), sh(1), 
> abs(6*synpar.W), 1, m, 'inh A');
> end
>
> Under PCSIM, I use 4 SimObjectVariationFactory (one for each type of 
> synapse: EE, EI, IE, II) and 4 ConnectionsProjection. Only the IE and 
> II weights have to be negative. I was thinking at using the 
> setFieldScale method in SimObjectPopulation. For instance for the II 
> connections this would give:
>
> liquid_syn[INH][INH] = 
> ConnectionsProjection(self.liquid_sub_populs[INH], 
> self.liquid_sub_populs[INH], syn_factory, 
> PredicateBasedConnections(EuclidianDistanceConnectionPredicate(C[INH][INH], 
> lambda_conn)))
> tmp_pop = SimObjectPopulation( liquid_syn[INH][INH].idVector() );
> tmp_pop.setFieldScale("W", -1);
I just wanted to say that I have tested this method and this seems to 
work (I have gamma-distributed negative weights).

Mathieu