solver_fluid_odes.m

function [ode_h,q_indices] = solver_fluid_odes(sn, N, Mu, phi, PH, P, nservers, sched, schedparam, options)
% [ODE_H,Q_INDICES] = SOLVER_FLUID_ODES(sn, N, MU, PHI, PH, P, NSERVERS, SCHED, SCHEDPARAM)
 
% Copyright (c) 2012-2026, Imperial College London
% All rights reserved.
 
M = length(nservers);    % number of stations
K = length(Mu{1});   % number of classes
w = ones(M,K);
 
enabled = false(M,K); % indicates whether a class is served at a station
% for i = 1:M
%     for c = 1:K
%         %enabled(i,c) = sum( P(:,(i-1)*K+c) ) > 0;
%         %changed to consider rows instead of columns, for response time
%         %analysis (first articial class never returns to delay node)
%         enabled(i,c) = sum( P((i-1)*K+c,:) ) > 0;
%     end
% end
 
q_indices = zeros(M,K);
Kic = zeros(M,K);
cumsum = 1;
for i = 1 : M
    for c = 1:K       
        if isnan(Mu{i}{c})
            numphases = 0;
            enabled(i,c) = false;
            q_indices(i,c) = cumsum;
        elseif isempty(Mu{i}{c})
            enabled(i,c) = false;
            numphases = 0;
            q_indices(i,c) = cumsum;
        else
            numphases = length(Mu{i}{c});            
            q_indices(i,c) = cumsum;
            enabled(i,c) = true;
        end
        Kic(i,c) = numphases;
        cumsum = cumsum + numphases;
    end
end
 
% to speed up convert sched strings in numerical values
for i = 1 : M
    switch sched(i) % source
        case SchedStrategy.DPS
            w(i,:) = schedparam(i,:);
    end
end
 
%% define ODE system to be returned
switch options.method
    case 'softmin'
        alpha = 20; % softmin parameter
        ode_sm_h = @(t,x) ode_softmin(x, phi, Mu, PH, M, K, enabled, q_indices, P, Kic, nservers, w, sched, alpha);
        ode_h = ode_sm_h;
    case 'pnorm'
        % p-norm smoothing method based on Ruuskanen et al., PEVA 151 (2021)
        if isfield(options, 'pstar') && ~isempty(options.pstar)
            pstar = options.pstar;
        else
            pstar = 20; % default p-norm parameter (similar behavior to softmin at alpha=20)
        end
        ode_pn_h = @(t,x) ode_pnorm(x, phi, Mu, PH, M, K, enabled, q_indices, P, Kic, nservers, w, sched, pstar);
        ode_h = ode_pn_h;
    case 'statedep'
        ode_sd_h = @(t,x) ode_statedep(x, phi, Mu, PH, M, K, enabled, q_indices, P, Kic, nservers, w, sched);
        ode_h = ode_sd_h;
    otherwise
        % determine all the jumps, and saves them for later use
        all_jumps = ode_jumps_new(M, K, enabled, q_indices, P, Kic);
        % determines a vector with the fixed part of the rates,
        % and defines the indexes that correspond to the events that occur
        [rateBase, eventIdx] = ode_rate_base(sn, phi, Mu, PH, M, K, enabled, q_indices, P, Kic, sched, all_jumps);
 
        % Eliminate immediate transitions if requested
        if isfield(options.config, 'hide_immediate') && options.config.hide_immediate
            if isfield(options, 'verbose') && options.verbose >= VerboseLevel.DEBUG
                fprintf('[DEBUG] Calling immediate elimination (hide_immediate=true)\n');
            end
            [all_jumps, rateBase, eventIdx, state_map] = ...
                ode_eliminate_immediate(all_jumps, rateBase, eventIdx, sn, options);
        else
            if isfield(options, 'verbose') && options.verbose >= VerboseLevel.DEBUG
                fprintf('[DEBUG] Skipping immediate elimination (hide_immediate=false)\n');
            end
        end
 
        ode_si_h = @(t,x) all_jumps * ode_rates_closing(x, M, K, enabled, q_indices, Kic, nservers, w, sched, rateBase, eventIdx);
        ode_h = ode_si_h;
end
end