Singular Manual: isHomogeneous

| #### D.15.13.37 isHomogeneous Procedure from library `multigrading.lib` (see multigrading_lib). Usage: isHomogeneous(a[, f]); a polynomial/vector/ideal/module Return: boolean, TRUE if a is (multi)homogeneous, and FALSE otherwise Example:
    LIB "multigrading.lib";
    ring r = 0,(x,y,z),dp;
    //Grading and Torsion matrices:
    intmat M[3][3] =
    1,0,0,
    0,1,0,
    0,0,1;
    intmat T[3][1] =
    1,2,3;
    setBaseMultigrading(M,T);
    attrib(r);
    ==> attr:cf_class, type int
    ==> attr:cf_class_Zp, type int
    ==> attr:cf_class_QQ, type int
    ==> attr:global, type int
    ==> attr:maxExp, type int
    ==> attr:ring_cf, type int
    ==> attr:isLetterplaceRing, type int
    ==> attr:gradingGroup, type list
    ==> attr:mgrad, type intmat
    poly f = x-yz;
    multiDegPartition(f);
    ==> _[1]=-yz
    ==> _[2]=x
    print(multiDeg(_));
    ==>      0     1
    ==>      1     0
    ==>      1     0
    isHomogeneous(f);   // f: is not homogeneous
    ==> 0
    poly g = 1-xy2z3;
    isHomogeneous(g); // g: is homogeneous
    ==> 1
    multiDegPartition(g);
    ==> _[1]=-xy2z3+1
    kill T;
    /////////////////////////////////////////////////////////
    // new Torsion matrix:
    intmat T[3][4] =
    3,3,3,3,
    2,1,3,0,
    1,2,0,3;
    setBaseMultigrading(M,T);
    f;
    ==> -yz+x
    isHomogeneous(f);
    ==> 0
    multiDegPartition(f);
    ==> _[1]=-yz
    ==> _[2]=x
    // ---------------------
    g;
    ==> -xy2z3+1
    isHomogeneous(g);
    ==> 0
    multiDegPartition(g);
    ==> _[1]=-xy2z3
    ==> _[2]=1
    kill r, T, M;
    ring R = 0, (x,y,z), dp;
    intmat A[2][3] =
    0,0,1,
    3,2,1;
    intmat T[2][1] =
    -1,
    4;
    setBaseMultigrading(A, T);
    isHomogeneous(ideal(x2 - y3 -xy +z, x*y-z, x^3 - y^2*z + x^2 -y^3)); // 1
    ==> 1
    isHomogeneous(ideal(x2 - y3 -xy +z, x*y-z, x^3 - y^2*z + x^2 -y^3), "checkGens");
    ==> 0
    isHomogeneous(ideal(x+y, x2 - y2)); // 0
    ==> 0
    // Degree partition:
    multiDegPartition(x2 - y3 -xy +z);
    ==> _[1]=-y3+x2
    ==> _[2]=-xy+z
    multiDegPartition(x3 -y2z + x2 -y3 + z + 1);
    ==> _[1]=x3-y2z
    ==> _[2]=-y3+x2
    ==> _[3]=z
    ==> _[4]=1
    module N = gen(1) + (x+y) * gen(2), z*gen(3);
    intmat V[2][3] = 0; // 1, 2, 3,  4, 5, 6; //  column-wise weights of components!!??
    vector v1, v2;
    v1 = setModuleGrading(N[1], V); v1;
    ==> x*gen(2)+y*gen(2)+gen(1)
    multiDegPartition(v1);
    ==> _[1]=x*gen(2)
    ==> _[2]=y*gen(2)
    ==> _[3]=gen(1)
    print( multiDeg(_) );
    ==>      0     0     0
    ==>      3     2     0
    v2 = setModuleGrading(N[2], V); v2;
    ==> z*gen(3)
    multiDegPartition(v2);
    ==> _[1]=z*gen(3)
    print( multiDeg(_) );
    ==>      1
    ==>      1
    N = setModuleGrading(N, V);
    isHomogeneous(N);
    ==> 0
    print( multiDeg(N) );
    ==>      0     1
    ==>      3     1
    ///////////////////////////////////////
    V =
    1, 2, 3,
    4, 5, 6;
    v1 = setModuleGrading(N[1], V); v1;
    ==> x*gen(2)+y*gen(2)+gen(1)
    multiDegPartition(v1);
    ==> _[1]=x*gen(2)
    ==> _[2]=y*gen(2)
    ==> _[3]=gen(1)
    print( multiDeg(_) );
    ==>      2     2     1
    ==>      8     7     4
    v2 = setModuleGrading(N[2], V); v2;
    ==> z*gen(3)
    multiDegPartition(v2);
    ==> _[1]=z*gen(3)
    print( multiDeg(_) );
    ==>      4
    ==>      7
    N = setModuleGrading(N, V);
    isHomogeneous(N);
    ==> 0
    print( multiDeg(N) );
    ==>      2     4
    ==>      8     7
    ///////////////////////////////////////
    V =
    0, 0, 0,
    4, 1, 0;
    N = gen(1) + x * gen(2), z*gen(3);
    N = setModuleGrading(N, V); print(N);
    ==> 1,0,
    ==> x,0,
    ==> 0,z
    isHomogeneous(N);
    ==> 1
    print( multiDeg(N) );
    ==>      0     1
    ==>      4     1
    v1 = getGradedGenerator(N,1); print(v1);
    ==> [1,x]
    multiDegPartition(v1);
    ==> _[1]=x*gen(2)+gen(1)
    print( multiDeg(_) );
    ==>      0
    ==>      4
    N = setModuleGrading(N, V); print(N);
    ==> 1,0,
    ==> x,0,
    ==> 0,z
    isHomogeneous(N);
    ==> 1
    print( multiDeg(N) );
    ==>      0     1
    ==>      4     1

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