Singular Manual: AltVarStart

| ##### 7.5.20.0. AltVarStart Procedure from library `nctools.lib` (see nctools_lib). Usage: AltVarStart(); Return: int Purpose: returns the number of the first alternating variable of basering Note: basering should be a super-commutative algebra constructed by the procedure `superCommutative`, emits an error otherwise Example:
    LIB "nctools.lib";
    ring R = 0,(x(1..4)),dp; // global!
    def ER = superCommutative(2); // (b = 2, e = N)
    setring ER; ER;
    ==> // coefficients: QQ considered as a field
    ==> // number of vars : 4
    ==> //        block   1 : ordering dp
    ==> //                  : names    x(1) x(2) x(3) x(4)
    ==> //        block   2 : ordering C
    ==> // noncommutative relations:
    ==> //    x(3)x(2)=-x(2)*x(3)
    ==> //    x(4)x(2)=-x(2)*x(4)
    ==> //    x(4)x(3)=-x(3)*x(4)
    ==> // quotient ring from ideal
    ==> _[1]=x(4)^2
    ==> _[2]=x(3)^2
    ==> _[3]=x(2)^2
    "Alternating variables: [", AltVarStart(), ",", AltVarEnd(), "].";
    ==> Alternating variables: [ 2 , 4 ].
    setring R;
    "Alternating variables: [", AltVarStart(), ",", AltVarEnd(), "].";
    ==>    ? SCA rings are factors by (at least) squares!
    ==>    ? leaving nctools.lib::AltVarStart (1133)
    kill R, ER;
    //////////////////////////////////////////////////////////////////
    ring R = 2,(x(1..4)),dp; // the same in char. = 2!
    def ER = superCommutative(2); // (b = 2, e = N)
    setring ER; ER;
    ==> // coefficients: ZZ/2 considered as a field
    ==> // number of vars : 4
    ==> //        block   1 : ordering dp
    ==> //                  : names    x(1) x(2) x(3) x(4)
    ==> //        block   2 : ordering C
    ==> // quotient ring from ideal
    ==> _[1]=x(4)^2
    ==> _[2]=x(3)^2
    ==> _[3]=x(2)^2
    "Alternating variables: [", AltVarStart(), ",", AltVarEnd(), "].";
    ==> Alternating variables: [ 4 , 4 ].
    setring R;
    "Alternating variables: [", AltVarStart(), ",", AltVarEnd(), "].";
    ==>    ? SCA rings are factors by (at least) squares!
    ==>    ? leaving nctools.lib::AltVarStart (1133)

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