function   e=polcheck(A,degA,B,degB,C,degC,D,degD)

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% calculates the relative error of    A-B*C*D            %
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% M. Sebek, November 1990                                %
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[At,degAt]=polmul(B,degB,C,degC);
[At,degAt]=polmul(At,degAt,D,degD);
[Dif,degDif]=poladd(A,degA,-At,degAt);

e=norm(Dif,inf)/norm(A,inf);