Constraint Handling in MPC, Vector plot using 'plot' command

I have written following program for MPC controller:

% A quadruple tank system consisting of four interconnected tanks** % No disturbance is considered, No model mismatch % MPC Control Action - Step by step Simulation

A1=28; A3=28; A2=32; A4=32; a1=0.071; a3=0.071; % Cross-section of outlet level a2=0.057; a4=0.057; % Cross-section of outlet level kc=0.5; g=981; k1=3.33; k2=3.35; r1=0.70; r2=0.60; h1= 12.4; % Level of water in tank1 h2=12.7; % Level of water in tank2 h3=1.8; % Level of water in tank3 h4=1.4; % Level of water in tank4

T1=(A1/a1)*(2*h1/g)^(1/2) % Time Constant T2=(A2/a2)*(2*h2/g)^(1/2) % Time Constant T3=(A3/a3)*(2*h3/g)^(1/2) % Time Constant T4=(A4/a4)*(2*h4/g)^(1/2) % Time Constant

A=[(-1/T1) 0 (A3/A1*T3) 0; 0 (-1/T2) 0 (A4/A2*A4); 0 0 (-1/T3) 0; 0 0 0 (-1/T4)] B=[(r1*k1/A1) 0; 0 (r2*k2/A2); 0 ((1-r2)*k2/A3); ((1-r1)*k1/A4) 0] C=[kc 0 0 0;0 kc 0 0] D=zeros(2,2)

sys=ss(A,B,C,D) % Continuous Time State Space Model

Ts=5; % Sampling Time model=c2d(sys,Ts) % Discrete time State Space Model [Ad,Bd,Cd,Dd] = c2dm(A,B,C,D,Ts)

%% Assign names to I/O variables (note: the model has no physical meaning)

model.InputName={'Voltage_Pump1';'Voltage_Pump2'}; model.OutputName={'Level_Tank1';'Level_Tank2'}; %model.InputUnit = {'V';'V'}; %model.OutputUnit = {'cm';'cm'};

%% Define I/O constraints and units

clear InputSpecs OutputSpecs InputSpecs(1)=struct('Min',-1,'Max',1,'RateMin',-0.1,'Ratemax',0.1); % Constraint on Voltage_Pump1 InputSpecs(2)=struct('Min',-1,'Max',1,'RateMin',-0.1,'Ratemax',0.1); % Constraint on Voltage_Pump2 OutputSpecs(1)=struct('Min',-5,'Max',5); % Constraint on Level_Tank1 OutputSpecs(2)=struct('Min',-5,'Max',5); % Constraint on Level_Tank2

%% Define weights on manipulated and controlled variables

Weights=struct('ManipulatedVariables',[1 1],... 'ManipulatedVariablesRate',[.1 .1],... 'OutputVariables',[1 1]);

%% Define prediction and control horizons, and set up the MPC object

ts=1; m=2; p=5;

MPCobj=mpc(model,ts,p,m,Weights,InputSpecs,OutputSpecs)

%% Closed-loop MPC Simulation Using the Command SIM

Tstop=30; % simulation time x=[0 0 0 0]'; % Initial state of the plant xmpc=mpcstate(MPCobj); % Initial State of the MPC controller r=[1 1]; % Output reference trajectory u=[0 0]';

%% Storage of closed loop MPC trajectories in arrays YY,UU,XX

YY=[]; UU=[]; XX=[];

%% Main Simulation Loop

for t=0:round(Tstop/ts)-1, XX=[XX,x];

    % Plant Equations: Output Update
    y=Cd*x;
    YY=[YY,y]

    % Compute MPC law
    u=mpcmove(MPCobj,xmpc,y,r)

    % Plant Equations: State Update
    x=Ad*x+Bd*u;
    UU=[UU,u];
end

%% Plot Results

close all

subplot(221) plot(0:ts:Tstop-Ts,YY(1)) grid title('Output_1')

subplot(222) plot(0:ts:Tstop-Ts,YY(2)) grid title('Output_2')

subplot(223) plot(0:ts:Tstop-Ts,UU(1)) grid title('Input_1')

subplot(224) plot(0:ts:Tstop-Ts,UU(2)) grid title('Input_2')

Problem is that it is not handling constraint on 'y'. Only constraints on 'u' are handled by the software. And how to plot two outputs in plot command or how to plot vector using plot command?