SOCP, problem 'Cone object cannot be negated'

[Scapa]

Hi

I tried the following minimal example of a second order cone program:

I use a rotated cone as constraint and two inequalities.

%%%%%%%%%%%%%%%%%%%%%%%%%

clear all

x = sdpvar(3,1);

Constraints = [rcone( x(3), 3 - x(1), 2 - x(2) ),    x(1) >= 0.6,  x(2) >= 0.6]

Objective = [0;0;-1]'*x;

options = sdpsettings('verbose',2,'showprogress',1,'solver','sedumi');%

sol = solvesdp(Constraints,Objective,options);

%%%%%%%%%%%%%%%%%%%%%%%%%

The solution should be: x = [0.6, 0.6, 2.5923]'

However, always the following error appears:

Error using sdpvar/uminus (line 25)

Cone object cannot be negated

Error in sdpvar/minus (line 255)

        y = addfactors(y,X,-Y);

Error in lmi/convertlorentz (line 17)

        F.clauses{i}.data = [(x+y)/sqrt(2);(x-y)/sqrt(2);z];

Error in compileinterfacedata (line 732)

    [F,changed] = convertlorentz(F);

Error in solvesdp (line 260)

[interfacedata,recoverdata,solver,diagnostic,F,Fremoved,ForiginalQuadratics] =

compileinterfacedata(F,[],logdetStruct,h,options,0,solving_parametric);

Error in temp (line 12)

sol = solvesdp(Constraints,Objective,options);

Where is the error in the formulation?

[Johan Löfberg]

There is no error in your code directly. However command rcone is supposed to be obsolete, I've forgotten to delete it.

Implement the condition z^z <= 2*x*y using norms

norm([sqrt(2)*x(3); (3 - x(1))-(2 - x(2))]) <=  (3 - x(1)) +  (2 - x(2))

which can be written using the low-level cone operator

cone([(3 - x(1)) +  (2 - x(2);2*x(3); (3 - x(1))-(2 - x(2))])

BTW, your objective is simply -x(3), no reason to introduce a vector to extract that element