function [VOI, STATES, ALGEBRAIC, CONSTANTS] = mainFunction()
    % This is the "main function".  In Matlab, things work best if you rename this function to match the filename.
   [VOI, STATES, ALGEBRAIC, CONSTANTS] = solveModel();
end

function [algebraicVariableCount] = getAlgebraicVariableCount() 
    % Used later when setting a global variable with the number of algebraic variables.
    % Note: This is not the "main method".  
    algebraicVariableCount =7;
end
% There are a total of 2 entries in each of the rate and state variable arrays.
% There are a total of 17 entries in the constant variable array.
%

function [VOI, STATES, ALGEBRAIC, CONSTANTS] = solveModel()
    % Create ALGEBRAIC of correct size
    global algebraicVariableCount;  algebraicVariableCount = getAlgebraicVariableCount();
    % Initialise constants and state variables
    [INIT_STATES, CONSTANTS] = initConsts;

    % Set timespan to solve over 
    tspan = [0, 10];

    % Set numerical accuracy options for ODE solver
    options = odeset('RelTol', 1e-06, 'AbsTol', 1e-06, 'MaxStep', 1);

    % Solve model with ODE solver
    [VOI, STATES] = ode15s(@(VOI, STATES)computeRates(VOI, STATES, CONSTANTS), tspan, INIT_STATES, options);

    % Compute algebraic variables
    [RATES, ALGEBRAIC] = computeRates(VOI, STATES, CONSTANTS);
    ALGEBRAIC = computeAlgebraic(ALGEBRAIC, CONSTANTS, STATES, VOI);

    % Plot state variables against variable of integration
    [LEGEND_STATES, LEGEND_ALGEBRAIC, LEGEND_VOI, LEGEND_CONSTANTS] = createLegends();
    figure();
    plot(VOI, STATES);
    xlabel(LEGEND_VOI);
    l = legend(LEGEND_STATES);
    set(l,'Interpreter','none');
end

function [LEGEND_STATES, LEGEND_ALGEBRAIC, LEGEND_VOI, LEGEND_CONSTANTS] = createLegends()
    LEGEND_STATES = ''; LEGEND_ALGEBRAIC = ''; LEGEND_VOI = ''; LEGEND_CONSTANTS = '';
    LEGEND_VOI = strpad('time in component environment (minute)');
    LEGEND_CONSTANTS(:,1) = strpad('MDFLW in component angiotensin (L_per_minute)');
    LEGEND_CONSTANTS(:,16) = strpad('ANGSCR in component instantaneous_angiotensin_formation (dimensionless)');
    LEGEND_CONSTANTS(:,15) = strpad('MDFLW3 in component instantaneous_angiotensin_formation (L_per_minute)');
    LEGEND_STATES(:,1) = strpad('ANX1 in component time_delayed_angiotensin_formation (dimensionless)');
    LEGEND_CONSTANTS(:,2) = strpad('ANXM in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,3) = strpad('ANV in component parameter_values (minute)');
    LEGEND_CONSTANTS(:,17) = strpad('ANX in component time_delayed_angiotensin_formation (dimensionless)');
    LEGEND_ALGEBRAIC(:,3) = strpad('ANPR in component total_angiotensin_formation (dimensionless)');
    LEGEND_CONSTANTS(:,4) = strpad('REK in component parameter_values (dimensionless)');
    LEGEND_ALGEBRAIC(:,1) = strpad('ANPRT in component total_angiotensin_formation (dimensionless)');
    LEGEND_ALGEBRAIC(:,5) = strpad('ANPR1 in component artificial_angiotensin_formation (dimensionless)');
    LEGEND_CONSTANTS(:,5) = strpad('ANGKNS in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,6) = strpad('ANGINF in component parameter_values (dimensionless)');
    LEGEND_STATES(:,2) = strpad('ANC in component angiotensin_concentration (dimensionless)');
    LEGEND_CONSTANTS(:,7) = strpad('ANT in component parameter_values (minute)');
    LEGEND_ALGEBRAIC(:,2) = strpad('ANM in component general_angiotensin_multiplier (dimensionless)');
    LEGEND_CONSTANTS(:,8) = strpad('ANMUL in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,9) = strpad('ANMLL in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,10) = strpad('ANCSNS in component parameter_values (dimensionless)');
    LEGEND_ALGEBRAIC(:,6) = strpad('ANU in component angiotensin_effect_on_circulation (dimensionless)');
    LEGEND_CONSTANTS(:,11) = strpad('ANUM in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,12) = strpad('ANULL in component parameter_values (dimensionless)');
    LEGEND_ALGEBRAIC(:,4) = strpad('ANU1 in component angiotensin_effect_on_circulation (dimensionless)');
    LEGEND_ALGEBRAIC(:,7) = strpad('ANUVN in component angiotensin_effect_on_venous_constriction (dimensionless)');
    LEGEND_CONSTANTS(:,13) = strpad('ANUVM in component parameter_values (dimensionless)');
    LEGEND_CONSTANTS(:,14) = strpad('Z12 in component parameter_values (dimensionless)');
    LEGEND_RATES(:,1) = strpad('d/dt ANX1 in component time_delayed_angiotensin_formation (dimensionless)');
    LEGEND_RATES(:,2) = strpad('d/dt ANC in component angiotensin_concentration (dimensionless)');
    LEGEND_STATES  = LEGEND_STATES';
    LEGEND_ALGEBRAIC = LEGEND_ALGEBRAIC';
    LEGEND_RATES = LEGEND_RATES';
    LEGEND_CONSTANTS = LEGEND_CONSTANTS';
end

function [STATES, CONSTANTS] = initConsts()
    VOI = 0; CONSTANTS = []; STATES = []; ALGEBRAIC = [];
    CONSTANTS(:,1) = 1.00051;
    STATES(:,1) = 0.0;
    CONSTANTS(:,2) = 0;
    CONSTANTS(:,3) = 5000;
    CONSTANTS(:,4) = 1;
    CONSTANTS(:,5) = 0;
    CONSTANTS(:,6) = 0;
    STATES(:,2) = 0.859476;
    CONSTANTS(:,7) = 12;
    CONSTANTS(:,8) = 1.8;
    CONSTANTS(:,9) = 0.7;
    CONSTANTS(:,10) = 0.4;
    CONSTANTS(:,11) = 6;
    CONSTANTS(:,12) = 0.8;
    CONSTANTS(:,13) = 0;
    CONSTANTS(:,14) = 5;
    CONSTANTS(:,15) = CONSTANTS(:,1);
    CONSTANTS(:,16) = piecewise({CONSTANTS(:,15)>1.00000, 1.00000./(1.00000+ (CONSTANTS(:,15) - 1.00000).*72.0000) }, 10.0000 - 9.00000./(1.00000+ (1.00000 - CONSTANTS(:,15)).*8.00000));
    CONSTANTS(:,17) =  (CONSTANTS(:,16) - 1.00000).*CONSTANTS(:,2);
    if (isempty(STATES)), warning('Initial values for states not set');, end
end

function [RATES, ALGEBRAIC] = computeRates(VOI, STATES, CONSTANTS)
    global algebraicVariableCount;
    statesSize = size(STATES);
    statesColumnCount = statesSize(2);
    if ( statesColumnCount == 1)
        STATES = STATES';
        ALGEBRAIC = zeros(1, algebraicVariableCount);
        utilOnes = 1;
    else
        statesRowCount = statesSize(1);
        ALGEBRAIC = zeros(statesRowCount, algebraicVariableCount);
        RATES = zeros(statesRowCount, statesColumnCount);
        utilOnes = ones(statesRowCount, 1);
    end
    RATES(:,1) = (CONSTANTS(:,17) - STATES(:,1))./CONSTANTS(:,3);
    ALGEBRAIC(:,1) =  (CONSTANTS(:,16)+STATES(:,1)).*CONSTANTS(:,4);
    ALGEBRAIC(:,3) = piecewise({ALGEBRAIC(:,1)<1.00000e-05, 1.00000e-05 }, ALGEBRAIC(:,1));
    ALGEBRAIC(:,5) = piecewise({CONSTANTS(:,5)>0.00000, CONSTANTS(:,5) }, ALGEBRAIC(:,3)+CONSTANTS(:,6));
    RATES(:,2) = (ALGEBRAIC(:,5) - STATES(:,2))./CONSTANTS(:,7);
   RATES = RATES';
end

% Calculate algebraic variables
function ALGEBRAIC = computeAlgebraic(ALGEBRAIC, CONSTANTS, STATES, VOI)
    statesSize = size(STATES);
    statesColumnCount = statesSize(2);
    if ( statesColumnCount == 1)
        STATES = STATES';
        utilOnes = 1;
    else
        statesRowCount = statesSize(1);
        utilOnes = ones(statesRowCount, 1);
    end
    ALGEBRAIC(:,1) =  (CONSTANTS(:,16)+STATES(:,1)).*CONSTANTS(:,4);
    ALGEBRAIC(:,3) = piecewise({ALGEBRAIC(:,1)<1.00000e-05, 1.00000e-05 }, ALGEBRAIC(:,1));
    ALGEBRAIC(:,5) = piecewise({CONSTANTS(:,5)>0.00000, CONSTANTS(:,5) }, ALGEBRAIC(:,3)+CONSTANTS(:,6));
    ALGEBRAIC(:,2) = CONSTANTS(:,8) - (CONSTANTS(:,8) - 1.00000)./( ((CONSTANTS(:,9) - 1.00000)./(CONSTANTS(:,9) - CONSTANTS(:,8))).*(STATES(:,2) - 1.00000).*CONSTANTS(:,10)+1.00000);
    ALGEBRAIC(:,4) =  (ALGEBRAIC(:,2) - 1.00000).*CONSTANTS(:,11)+1.00000;
    ALGEBRAIC(:,6) = piecewise({ALGEBRAIC(:,4)<CONSTANTS(:,12), CONSTANTS(:,12) }, ALGEBRAIC(:,4));
    ALGEBRAIC(:,7) =  (ALGEBRAIC(:,6) - 1.00000).*CONSTANTS(:,13)+1.00000;
end

% Compute result of a piecewise function
function x = piecewise(cases, default)
    set = [0];
    for i = 1:2:length(cases)
        if (length(cases{i+1}) == 1)
            x(cases{i} & ~set,:) = cases{i+1};
        else
            x(cases{i} & ~set,:) = cases{i+1}(cases{i} & ~set);
        end
        set = set | cases{i};
        if(set), break, end
    end
    if (length(default) == 1)
        x(~set,:) = default;
    else
        x(~set,:) = default(~set);
    end
end

% Pad out or shorten strings to a set length
function strout = strpad(strin)
    req_length = 160;
    insize = size(strin,2);
    if insize > req_length
        strout = strin(1:req_length);
    else
        strout = [strin, blanks(req_length - insize)];
    end
end