function [MVAbase, bus, gen, branch, success, et] = ...
                runpf(casename, mpopt, fname, solvedcase)
%RUNPF  Runs a power flow.
%
%   Output arguments options:
%
%   results = runpf(...)
%   [results, success] = runpf(...)
%   [baseMVA, bus, gen, branch, success, et] = runpf(...)
%
%   Input arguments options:
%
%   runpf(casename)
%   runpf(casename, mpopt)
%   runpf(casename, mpopt, fname)
%   runpf(casename, mpopt, fname, solvedcase)
%
%   Runs a power flow (full AC Newton's method by default) and optionally
%   returns the solved values in the data matrices, a flag which is true if
%   the algorithm was successful in finding a solution, and the elapsed time
%   in seconds. Alternatively, the solution can be returned as fields in a
%   results struct and an optional success flag.
%
%   All input arguments are optional. If casename is provided it specifies
%   the name of the input data file or struct (see also 'help caseformat' and
%   'help loadcase') containing the power flow data. The default value is
%   'case9'. If the mpopt is provided it overrides the default MATPOWER options
%   vector and can be used to specify the solution algorithm and output options
%   among other things (see 'help mpoption' for details). If the 3rd argument
%   is given the pretty printed output will be appended to the file whose name
%   is given in fname. If solvedcase is specified the solved case will be
%   written to a case file in MATPOWER format with the specified name. If
%   solvedcase ends with '.mat' it saves the case as a MAT-file otherwise it
%   saves it as an M-file.
%
%   If the ENFORCE_Q_LIMS options is set to true (default is false) then if
%   any generator reactive power limit is violated after running the AC power
%   flow, the corresponding bus is converted to a PQ bus, with Qg at the
%   limit, and the case is re-run. The voltage magnitude at the bus will
%   deviate from the specified value in order to satisfy the reactive power
%   limit. If the reference bus is converted to PQ, the first remaining PV
%   bus will be used as the slack bus for the next iteration. This may
%   result in the real power output at this generator being slightly off
%   from the specified values.

%   MATPOWER
%   $Id: runpf.m,v 1.19 2009/12/04 18:58:38 ray Exp $
%   by Ray Zimmerman, PSERC Cornell
%   Enforcing of generator Q limits inspired by contributions
%   from Mu Lin, Lincoln University, New Zealand (1/14/05).
%   Copyright (c) 1996-2005 by Power System Engineering Research Center (PSERC)
%   See http://www.pserc.cornell.edu/matpower/ for more info.

%%-----  initialize  -----
%% define named indices into bus, gen, branch matrices
[PQ, PV, REF, NONE, BUS_I, BUS_TYPE, PD, QD, GS, BS, BUS_AREA, VM, ...
    VA, BASE_KV, ZONE, VMAX, VMIN, LAM_P, LAM_Q, MU_VMAX, MU_VMIN] = idx_bus;
[F_BUS, T_BUS, BR_R, BR_X, BR_B, RATE_A, RATE_B, RATE_C, ...
    TAP, SHIFT, BR_STATUS, PF, QF, PT, QT, MU_SF, MU_ST, ...
    ANGMIN, ANGMAX, MU_ANGMIN, MU_ANGMAX] = idx_brch;
[GEN_BUS, PG, QG, QMAX, QMIN, VG, MBASE, GEN_STATUS, PMAX, PMIN, ...
    MU_PMAX, MU_PMIN, MU_QMAX, MU_QMIN, PC1, PC2, QC1MIN, QC1MAX, ...
    QC2MIN, QC2MAX, RAMP_AGC, RAMP_10, RAMP_30, RAMP_Q, APF] = idx_gen;

%% default arguments
if nargin < 4
    solvedcase = '';                %% don't save solved case
    if nargin < 3
        fname = '';                 %% don't print results to a file
        if nargin < 2
            mpopt = mpoption;       %% use default options
            if nargin < 1
                casename = 'case9'; %% default data file is 'case9.m'
            end
        end
    end
end

%% options
verbose = mpopt(31);
qlim = mpopt(6);                    %% enforce Q limits on gens?
dc = mpopt(10);                     %% use DC formulation?

%% read data
mpc = loadcase(casename);

%% add zero columns to branch for flows if needed
if size(mpc.branch,2) < QT
  mpc.branch = [ mpc.branch zeros(size(mpc.branch, 1), QT-size(mpc.branch,2)) ];
end

%% convert to internal indexing
mpc = ext2int(mpc);
[baseMVA, bus, gen, branch] = deal(mpc.baseMVA, mpc.bus, mpc.gen, mpc.branch);

%% get bus index lists of each type of bus
[ref, pv, pq] = bustypes(bus, gen);

%% generator info
on = find(gen(:, GEN_STATUS) > 0);      %% which generators are on?
gbus = gen(on, GEN_BUS);                %% what buses are they at?

%%-----  run the power flow  -----
t0 = clock;
if dc                               %% DC formulation
    %% initial state
    Va0 = bus(:, VA) * (pi/180);
    
    %% build B matrices and phase shift injections
    [B, Bf, Pbusinj, Pfinj] = makeBdc(baseMVA, bus, branch);
    
    %% compute complex bus power injections (generation - load)
    %% adjusted for phase shifters and real shunts
    Pbus = real(makeSbus(baseMVA, bus, gen)) - Pbusinj - bus(:, GS) / baseMVA;
    
    %% "run" the power flow
    Va = dcpf(B, Pbus, Va0, ref, pv, pq);
    
    %% update data matrices with solution
    branch(:, [QF, QT]) = zeros(size(branch, 1), 2);
    branch(:, PF) = (Bf * Va + Pfinj) * baseMVA;
    branch(:, PT) = -branch(:, PF);
    bus(:, VM) = ones(size(bus, 1), 1);
    bus(:, VA) = Va * (180/pi);
    %% update Pg for swing generator (note: other gens at ref bus are accounted for in Pbus)
    %%      Pg = Pinj + Pload + Gs
    %%      newPg = oldPg + newPinj - oldPinj
    refgen = find(gbus == ref);             %% which is(are) the reference gen(s)?
    gen(on(refgen(1)), PG) = gen(on(refgen(1)), PG) + (B(ref, :) * Va - Pbus(ref)) * baseMVA;
    
    success = 1;
else                                %% AC formulation
    %% initial state
    % V0    = ones(size(bus, 1), 1);            %% flat start
    V0  = bus(:, VM) .* exp(sqrt(-1) * pi/180 * bus(:, VA));
    V0(gbus) = gen(on, VG) ./ abs(V0(gbus)).* V0(gbus);
    
    if qlim
        ref0 = ref;                         %% save index and angle of
        Varef0 = bus(ref0, VA);             %%   original reference bus
        limited = [];                       %% list of indices of gens @ Q lims
        fixedQg = zeros(size(gen, 1), 1);   %% Qg of gens at Q limits
    end
    repeat = 1;
    while (repeat)
        %% build admittance matrices
        [Ybus, Yf, Yt] = makeYbus(baseMVA, bus, branch);
        
        %% compute complex bus power injections (generation - load)
        Sbus = makeSbus(baseMVA, bus, gen);
        
        %% run the power flow
        alg = mpopt(1);
        if alg == 1
            [V, success, iterations] = newtonpf(Ybus, Sbus, V0, ref, pv, pq, mpopt);
        elseif alg == 2 || alg == 3
            [Bp, Bpp] = makeB(baseMVA, bus, branch, alg);
            [V, success, iterations] = fdpf(Ybus, Sbus, V0, Bp, Bpp, ref, pv, pq, mpopt);
        elseif alg == 4
            [V, success, iterations] = gausspf(Ybus, Sbus, V0, ref, pv, pq, mpopt);
        else
            error('Only Newton''s method, fast-decoupled, and Gauss-Seidel power flow algorithms currently implemented.');
        end
        
        %% update data matrices with solution
        [bus, gen, branch] = pfsoln(baseMVA, bus, gen, branch, Ybus, Yf, Yt, V, ref, pv, pq);
        
        if qlim             %% enforce generator Q limits
            %% find gens with violated Q constraints
            mx = find( gen(:, GEN_STATUS) > 0 & gen(:, QG) > gen(:, QMAX) );
            mn = find( gen(:, GEN_STATUS) > 0 & gen(:, QG) < gen(:, QMIN) );
            
            if ~isempty(mx) || ~isempty(mn)  %% we have some Q limit violations
                if isempty(pv)
                    if verbose
                        if ~isempty(mx) 
                            fprintf('Gen %d (only one left) exceeds upper Q limit : INFEASIBLE PROBLEM\n', mx);
                        else
                            fprintf('Gen %d (only one left) exceeds lower Q limit : INFEASIBLE PROBLEM\n', mn);
                        end
                    end
                    success = 0;
                    break;
                end

                %% one at a time?
                if qlim == 2    %% fix largest violation, ignore the rest
                    [junk, k] = max([gen(mx, QG) - gen(mx, QMAX);
                                     gen(mn, QMIN) - gen(mn, QG)]);
                    if k > length(mx)
                        mn = mn(k-length(mx));
                        mx = [];
                    else
                        mx = mx(k);
                        mn = [];
                    end
                end

                if verbose && ~isempty(mx)
                    fprintf('Gen %d at upper Q limit, converting to PQ bus\n', mx);
                end
                if verbose && ~isempty(mn)
                    fprintf('Gen %d at lower Q limit, converting to PQ bus\n', mn);
                end
                
                %% save corresponding limit values
                fixedQg(mx) = gen(mx, QMAX);
                fixedQg(mn) = gen(mn, QMIN);
                mx = [mx;mn];
                
                %% convert to PQ bus
                gen(mx, QG) = fixedQg(mx);      %% set Qg to binding limit
                gen(mx, GEN_STATUS) = 0;        %% temporarily turn off gen,
                for i = 1:length(mx)            %% (one at a time, since
                    bi = gen(mx(i), GEN_BUS);   %%  they may be at same bus)
                    bus(bi, [PD,QD]) = ...      %% adjust load accordingly,
                        bus(bi, [PD,QD]) - gen(mx(i), [PG,QG]);
                end
                bus(gen(mx, GEN_BUS), BUS_TYPE) = PQ;   %% & set bus type to PQ
                
                %% update bus index lists of each type of bus
                ref_temp = ref;
                [ref, pv, pq] = bustypes(bus, gen);
                if verbose && ref ~= ref_temp
                    fprintf('Bus %d is new slack bus\n', ref);
                end
                limited = [limited; mx];
            else
                repeat = 0; %% no more generator Q limits violated
            end
        else
            repeat = 0;     %% don't enforce generator Q limits, once is enough
        end
    end
    if qlim && ~isempty(limited)
        %% restore injections from limited gens (those at Q limits)
        gen(limited, QG) = fixedQg(limited);    %% restore Qg value,
        for i = 1:length(limited)               %% (one at a time, since
            bi = gen(limited(i), GEN_BUS);      %%  they may be at same bus)
            bus(bi, [PD,QD]) = ...              %% re-adjust load,
                bus(bi, [PD,QD]) + gen(limited(i), [PG,QG]);
        end
        gen(limited, GEN_STATUS) = 1;               %% and turn gen back on
        if ref ~= ref0
            %% adjust voltage angles to make original ref bus correct
            bus(:, VA) = bus(:, VA) - bus(ref0, VA) + Varef0;
        end
    end
end
mpc.et = etime(clock, t0);
mpc.success = success;

%%-----  output results  -----
%% convert back to original bus numbering & print results
[mpc.bus, mpc.gen, mpc.branch] = deal(bus, gen, branch);
results = int2ext(mpc);

%% zero out result fields of out-of-service gens & branches
if ~isempty(results.order.gen.status.off)
  results.gen(results.order.gen.status.off, [PG QG]) = 0;
end
if ~isempty(results.order.branch.status.off)
  results.branch(results.order.branch.status.off, [PF QF PT QT]) = 0;
end

if fname
    [fd, msg] = fopen(fname, 'at');
    if fd == -1
        error(msg);
    else
        printpf(results, fd, mpopt);
        fclose(fd);
    end
end
printpf(results, 1, mpopt);

%% save solved case
if solvedcase
    savecase(solvedcase, results);
end

if nargout == 1 || nargout == 2
    MVAbase = results;
    bus = success;
elseif nargout > 2
    [MVAbase, bus, gen, branch, et] = ...
        deal(results.baseMVA, results.bus, results.gen, results.branch, results.et);
% else  %% don't define MVAbase, so it doesn't print anything
end
