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This paper presents a method of analyzing the stability of linear time-invariant interconnected systems with uncertainties: each subsystem is single-input single-output and its vector locus lies inside a polygon at each frequency. It is shown that the convex closure of the image of the Cartesian product of these polygons under the mapping agrees with the convex closure of the image of the vertices of these polygons under the mapping φ. From this result the image can be estimated by a finite Dumber of calculations. A sufficient stability condition is obtained by applying this result to the multivariable Nyquist stability criterion.