%%*********************************************************
%% Atyfun: compute sum_{k=1}^m yk*Ak.
%%
%%  Q = Atyfun(blk,At,permA,isspAy,y);
%%
%% Note: permA and isspAy may be set to [].
%%
%% SDPT3: version 3.1
%% Copyright (c) 1997 by
%% K.C. Toh, M.J. Todd, R.H. Tutuncu
%% Last Modified: 16 Sep 2004
%%**********************************************************

function Q = Atyfun(blk,At,permA,isspAy,y)

if isempty(permA); ismtpermA = 1; else ismtpermA = 0; end

Q = cell(size(blk,1),1);
if isempty(isspAy); isspAy = ones(size(blk,1),1); end
for p = 1:size(blk,1)
    pblk = blk(p,:);
    if strcmp(pblk{1},'s')
        n = sum(pblk{2});
        m1 = size(At{p,1},2);
        if (~isempty(At{p,1}))
            if (ismtpermA)
                tmp = At{p,1}*y(1:m1);
            else
                tmp = At{p,1}*y(permA(p,1:m1),1);
            end
            Q{p} = smat(pblk,tmp,isspAy(p));
        else
            Q{p} = sparse(n,n);
        end
        if (length(pblk) > 2) %% for low rank constraints
            len = sum(pblk{3});
            m2 = length(pblk{3});
            y2 = y(m1+1:m1+m2);
            dd = At{p,3};
            idxD = [0; find(diff(dd(:,1))); size(dd,1)];
            yy2 = mexexpand(diff(idxD),y2);
            DD = spconvert([dd(:,2:3),dd(:,4).*yy2; len,len,0]);
            Q{p} = Q{p} + At{p,2}*DD*At{p,2}';
        end
    else
        Q{p} = At{p,1}*y;
    end
end
%%*********************************************************

