"permute" command for sdpvar

[reza mehrabadi]

Hi All. Due to time problems with "for" loops, i wanted to restate the following code (located inside 4 "for" loops):

pij=sdpvar(B,B,T,H);
.
.
.
constr=[constr,pij(i,j,t,h)+pij(j,i,t,h)==0];

changed to (without need for any loop):

constr=[constr,pij+permute(pij,[2 1 3 4])==0];

Error in sdpvar/permute (line 8)

X.dim = X.dim(p);

[Johan Löfberg]

What dimensions do you have. Works here, and the error message signals that you don't have an nd-array (called ndsdpvar internally) but a standard 2d array (sdpvar) due to singleton trailing dimensions

>> X = sdpvar(2,3,4,5);

>> permute(X,[4 3 1 2])

Multi-dimensional SDPVAR object 5x4x2x3

>> X = sdpvar(2,3,1,1);

>> permute(X,[4 3 1 2])

Index exceeds array bounds.

[reza mehrabadi]

Well. Thanks. Yes the size has single dimensions like: 

pij=sdpvar(39,39,1,1,'full');
permute(X,[2 1 3 4]);

I can change the size but anyway to work with singles?

[Johan Löfberg]

it's simply not supported at the moment, you will have to do some clever combination of standard 2d matrix + permute  + reshape or something

>> x = sdpvar(2);reshape(permute(x,[2 1]),1,1,2,2)

Multi-dimensional SDPVAR object 1x1x2x2

or somehing like that, perhaps

[Johan Löfberg]

add to top of sdpvar/permute

if length(X.dim) < length(p)

    X = ndsdpvar(X);        

    X = permute(X,p);

    return

end

and this to top of ndsdpvar/permute

if length(X.dim) < length(p)
    X.dim = [X.dim ones(1,length(p)-length(X.dim))];
end

after that, it should work

>> X = sdpvar(2,3);

>> Y = randn(2,3);assign(X,Y);

>> d = permute(X,[4 3 2 1])-permute(Y,[4 3 2 1]);norm(value(d(:)))

ans =

     0

[reza mehrabadi]

Thank you very much. I've changed single dimensions into something else and problem solved (in addition to significant yalmiptime reduction). Maybe you can apply this to the next version!

[Johan Löfberg]

Yes this is of course added to the code as it is expected MATLAB syntax