You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_lotka_volterra.m
    path of file: ./repos/spm12
    
    the code of the file until where you have to start completion: function [f] = spm_lotka_volterra(x,v,P)
% equations of motion for Lotka-Volterra dynamics
% FORMAT [f] = spm_lotka_volterra(x,v,P)
% FORMAT [f] = spm_lotka_volterra(x,v)
% FORMAT [P] = spm_lotka_volterra(n)
%
% x     - hidden states
% v     - parameter of P.f
% P     - lateral connectivity
%
% returns f = dx/dt = P*S(x) - x/8 + 1;
%              S(x) = 1./(1 + exp(-x))
%
% where P determines the order of unstable fixed points visited in the
% stable heteroclinic channel. If P is not specified it will be computed
% using v. If x is a scalar a matrix of size x (P) is returned (with v = 1).

    
function [f] = spm_lotka_volterra(x,v,P)
% equations of motion for Lotka-Volterra dynamics
% FORMAT [f] = spm_lotka_volterra(x,v,P)
% FORMAT [f] = spm_lotka_volterra(x,v)
% FORMAT [P] = spm_lotka_volterra(n)
%
% x     - hidden states
% v     - parameter of P.f
% P     - lateral connectivity
%
% returns f = dx/dt = P*S(x) - x/8 + 1;
%              S(x) = 1./(1 + exp(-x))
%
% where P determines the order of unstable fixed points visited in the
% stable heteroclinic channel. If P is not specified it will be computed
% using v. If x is a scalar a matrix of size x (P) is returned (with v = 1).
%
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_lotka_volterra.m 6353 2015-03-01 11:52:49Z karl $


% intialise
%==========================================================================
try, v; catch, v = 1; end