DASHREPLACE_WITH_DASH_DASH- MC loop

       % sample a (blend of new & old) design matrix
       A = (1-newA)*A0 + newA*(randn(m,n));  % Gaussian update
       %A = (1-newA)*A0 + newA*(rand(m,n));  % Uniform update

       % sample a new x0
       x0 = randn(n,1);         % Gaussian x
       %x0 = 3*(2*rand(n,1)-1);  % Uniform x
       %x0 = sign(randn(n,1));   % Binary x

       % true x0 is k0-sparse  (recovered x will be k-sparse)
       idx = randperm(n);
       x0(idx(1:n-k0)) = 0;
      