Spot operator: opMask Spot Home Page
opMask
 opMask  Selection mask.
 
    opMask(N,IDX) creates a diagonal N-by-N operator that has ones
    only on those locations indicated by IDX.
 
    opMask(IDX) is the same as opMask(numel(IDX),IDX) when parameter
    IDX is logical.
See also