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 3 entries in each of the rate and state variable arrays.
% There are a total of 14 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 (millisecond)');
    LEGEND_STATES(:,1) = strpad('V in component V (millivolt)');
    LEGEND_CONSTANTS(:,1) = strpad('C in component V (microF_per_cm2)');
    LEGEND_CONSTANTS(:,2) = strpad('i_app in component V (microA_per_cm2)');
    LEGEND_ALGEBRAIC(:,1) = strpad('i_L in component i_L (microA_per_cm2)');
    LEGEND_ALGEBRAIC(:,4) = strpad('i_Ca in component i_Ca (microA_per_cm2)');
    LEGEND_ALGEBRAIC(:,7) = strpad('i_K in component i_K (microA_per_cm2)');
    LEGEND_CONSTANTS(:,3) = strpad('g_L in component i_L (milliS_per_cm2)');
    LEGEND_CONSTANTS(:,4) = strpad('E_L in component i_L (millivolt)');
    LEGEND_CONSTANTS(:,5) = strpad('E_Ca in component i_Ca (millivolt)');
    LEGEND_CONSTANTS(:,6) = strpad('g_Ca in component i_Ca (milliS_per_cm2)');
    LEGEND_STATES(:,2) = strpad('m in component i_Ca_m_gate (dimensionless)');
    LEGEND_ALGEBRAIC(:,2) = strpad('m_infinity in component i_Ca_m_gate (dimensionless)');
    LEGEND_ALGEBRAIC(:,5) = strpad('lambda_m in component i_Ca_m_gate (per_millisecond)');
    LEGEND_CONSTANTS(:,7) = strpad('lambda_m_bar in component i_Ca_m_gate (per_millisecond)');
    LEGEND_CONSTANTS(:,8) = strpad('V1 in component i_Ca_m_gate (millivolt)');
    LEGEND_CONSTANTS(:,9) = strpad('V2 in component i_Ca_m_gate (millivolt)');
    LEGEND_CONSTANTS(:,10) = strpad('E_K in component i_K (millivolt)');
    LEGEND_CONSTANTS(:,11) = strpad('g_K in component i_K (milliS_per_cm2)');
    LEGEND_STATES(:,3) = strpad('n in component i_K_n_gate (dimensionless)');
    LEGEND_ALGEBRAIC(:,3) = strpad('n_infinity in component i_K_n_gate (dimensionless)');
    LEGEND_ALGEBRAIC(:,6) = strpad('lambda_n in component i_K_n_gate (per_millisecond)');
    LEGEND_CONSTANTS(:,12) = strpad('lambda_n_bar in component i_K_n_gate (per_millisecond)');
    LEGEND_CONSTANTS(:,13) = strpad('V3 in component i_K_n_gate (millivolt)');
    LEGEND_CONSTANTS(:,14) = strpad('V4 in component i_K_n_gate (millivolt)');
    LEGEND_RATES(:,1) = strpad('d/dt V in component V (millivolt)');
    LEGEND_RATES(:,2) = strpad('d/dt m in component i_Ca_m_gate (dimensionless)');
    LEGEND_RATES(:,3) = strpad('d/dt n in component i_K_n_gate (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 = [];
    STATES(:,1) = -50;
    CONSTANTS(:,1) = 20.0;
    CONSTANTS(:,2) = 540.0;
    CONSTANTS(:,3) = 2.0;
    CONSTANTS(:,4) = -50.00;
    CONSTANTS(:,5) = 100.0;
    CONSTANTS(:,6) = 4.0;
    STATES(:,2) = 0.1;
    CONSTANTS(:,7) = 1.0;
    CONSTANTS(:,8) = 0.0;
    CONSTANTS(:,9) = 15.0;
    CONSTANTS(:,10) = -70.0;
    CONSTANTS(:,11) = 8.0;
    STATES(:,3) = 0.1;
    CONSTANTS(:,12) = 0.1;
    CONSTANTS(:,13) = 10.0;
    CONSTANTS(:,14) = 10.0;
    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
    ALGEBRAIC(:,2) =  0.500000.*(1.00000+ tanh((STATES(:,1) - CONSTANTS(:,8))./CONSTANTS(:,9)));
    ALGEBRAIC(:,5) =  CONSTANTS(:,7).*cosh((STATES(:,1) - CONSTANTS(:,8))./( 2.00000.*CONSTANTS(:,9)));
    RATES(:,2) =  ALGEBRAIC(:,5).*(ALGEBRAIC(:,2) - STATES(:,2));
    ALGEBRAIC(:,3) =  0.500000.*(1.00000+ tanh((STATES(:,1) - CONSTANTS(:,13))./CONSTANTS(:,14)));
    ALGEBRAIC(:,6) =  CONSTANTS(:,12).*cosh((STATES(:,1) - CONSTANTS(:,13))./( 2.00000.*CONSTANTS(:,14)));
    RATES(:,3) =  ALGEBRAIC(:,6).*(ALGEBRAIC(:,3) - STATES(:,3));
    ALGEBRAIC(:,1) =  CONSTANTS(:,3).*(STATES(:,1) - CONSTANTS(:,4));
    ALGEBRAIC(:,4) =  CONSTANTS(:,6).*STATES(:,2).*(STATES(:,1) - CONSTANTS(:,5));
    ALGEBRAIC(:,7) =  CONSTANTS(:,11).*STATES(:,3).*(STATES(:,1) - CONSTANTS(:,10));
    RATES(:,1) = (CONSTANTS(:,2) - (ALGEBRAIC(:,1)+ALGEBRAIC(:,4)+ALGEBRAIC(:,7)))./CONSTANTS(:,1);
   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(:,2) =  0.500000.*(1.00000+ tanh((STATES(:,1) - CONSTANTS(:,8))./CONSTANTS(:,9)));
    ALGEBRAIC(:,5) =  CONSTANTS(:,7).*cosh((STATES(:,1) - CONSTANTS(:,8))./( 2.00000.*CONSTANTS(:,9)));
    ALGEBRAIC(:,3) =  0.500000.*(1.00000+ tanh((STATES(:,1) - CONSTANTS(:,13))./CONSTANTS(:,14)));
    ALGEBRAIC(:,6) =  CONSTANTS(:,12).*cosh((STATES(:,1) - CONSTANTS(:,13))./( 2.00000.*CONSTANTS(:,14)));
    ALGEBRAIC(:,1) =  CONSTANTS(:,3).*(STATES(:,1) - CONSTANTS(:,4));
    ALGEBRAIC(:,4) =  CONSTANTS(:,6).*STATES(:,2).*(STATES(:,1) - CONSTANTS(:,5));
    ALGEBRAIC(:,7) =  CONSTANTS(:,11).*STATES(:,3).*(STATES(:,1) - CONSTANTS(:,10));
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