How do I know the number of the hidden nodes in ANN ?

[I N ] = size(input)         % size("I"nput)

[O N ] = size(target)        % size("O"utput)

Ntrn   = N - 2*round(0.15*N) % Default no. of training examples ~ 0.7*N

Ntrneq = Ntrn*O              % No. of training equations 

Nw     = (I+1)*H +(H+1)*O    % No. of unknown weights for H = number of hidden nodes

     Hub = -1 + ceil( (Ntrneq - O) / (I+O+1) ) % integer H

     net.trainPerform.goal = 0.01*mean(var(target',1)))

     0 <= Hmin <= H <= Hmax <= Hub

     Validation Stopping and/or regularization (e.g., msereg or TRAINBR}