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84  Quadratic constraint problem

Paper: LINEAR-QUADRATIC OPTIMAL CONTROL WITH INTEGRAL QUADRATIC CONSTRAINTS. OPTIMAL CONTROL APPLICATIONS AND METHODS Optim. Control Appl. Meth., 20, 79-92 (1999)

E. B. LIM(1), Y. Q. LIU(2), K. L. TEO(2) AND J. B. MOORE(1)

(1) Department of Systems Engineering, Research School of Information Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia

(2) School of Mathematics and Statistics, Curtin University of Technology, Perth, WA 6845, Australia

84.1  Problem Formulation

Find u(t) over t in [0; 1 ] to minimize

J = 0.5*x1(1)2 + 0.5*

∫

1 0

(x12 + u12 + u22) dt

subject to:

dx1 dt

= 3*x1+x2 + u1

dx2 dt

= −x1+2*x2 + u2

x1(0) = 4

x2(0) = −4

0.5*x2(1)2 + 0.5*

∫

1 0

(x12 + u12 + u22) <= 80

Introduce a new variable to remove integral in constraint:

dx3 dt

= 0.5 * (x1.2 + u1.2 + u2.2)

resulting in event constraint:

0.5*x2(1)2 + x3(1) <= 8

Reference: [23]

84.2  Problem setup

toms t
p = tomPhase('p', t, 0, 1, 50);
setPhase(p);

tomStates x1 x2 x3
tomControls u1 u2

% Initial guess
x0 = {icollocate({
    x1 == 4-5*t
    x2 == -4-1*t
    x3 == 50*t
    })
    collocate({
    u1 == -10+10*t
    u2 == 14-12*t})};

% Boundary constraints
cbnd = {
    initial({
    x1 == 4
    x2 == -4
    x3 == 0
    })
    final(x2)^2/2+final(x3) <= 80};

% ODEs and path constraints
ceq = collocate({
    dot(x1) == 3*x1+x2 + u1
    dot(x2) == -x1+2*x2 + u2
    dot(x3) == 1/2 * (x2.^2 + u1.^2 + u2.^2)
    });

% Objective
objective = final(x1)^2/2 + final(x3);

84.3  Solve the problem

options = struct;
options.name = 'Quadratic Constraint';
solution = ezsolve(objective, {cbnd, ceq}, x0, options);
t  = subs(collocate(t),solution);
x1 = subs(collocate(x1),solution);
x2 = subs(collocate(x2),solution);
x3 = subs(collocate(x3),solution);
u1 = subs(collocate(u1),solution);
u2 = subs(collocate(u2),solution);

Problem type appears to be: qpcon
Starting numeric solver
===== * * * =================================================================== * * *
TOMLAB - Tomlab Optimization Inc. Development license  999001. Valid to 2010-02-05
=====================================================================================
Problem: ---  1: Quadratic Constraint           f_k      67.888740121887395000
                                       sum(|constr|)      0.000000192425266868
                              f(x_k) + sum(|constr|)     67.888740314312656000
                                              f(x_0)     50.499999999999943000

Solver: snopt.  EXIT=0.  INFORM=1.
SNOPT 7.2-5 NLP code
Optimality conditions satisfied

FuncEv    1 ConstrEv   32 ConJacEv   32 Iter   31 MinorIter  280
CPU time: 0.546875 sec. Elapsed time: 0.547000 sec.

84.4  Plot result

subplot(2,1,1)
plot(t,x1,'*-',t,x2,'*-',t,x3/10,'*-');
legend('x1','x2','x3/10');
title('Quadratic Constraint state variables');

subplot(2,1,2)
plot(t,u1,'+-',t,u2,'+-');
legend('u1','u2');
title('Quadratic Constraint control');

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