Singular Manual: coneViaPoints

| #### D.13.2.7 coneViaPoints Procedure from library `gfan.lib` (see gfan_lib). Usage: coneViaPoints(HL); intmat HL coneViaPoints(HL,L); intmat HL, intmat L coneViaPoints(HL,L,flags); intmat HL, intmat L, int flags Return: cone Purpose: cone generated by half lines generated by the row vectors of HL and (if stated) by lines generated by the row vectors of L; flags may range between 0,..,3 defining an upper and lower bit (0=0*2+0, 1=0*2+1, 2=1*2+0, 3=1*2+1), if upper bit is 1, then program assumes that each row vector in HL generates a ray of the cone, if lower bit is 1, then program assumes that the span of the row vectors of L is the lineality space of the cone, if either bit is 0, then program computes the information itself. Example:
    LIB "gfan.lib";
    // Let's define a cone in R^3 generated by the following half lines:
    intmat HL[5][3]=
    1,0, 0,
    -1,0, 0,
    0,1, 1,
    0,1,-1,
    0,0, 1;
    cone c=coneViaPoints(HL);
    c;
    ==> AMBIENT_DIM
    ==> 3
    ==> FACETS
    ==> 0,1,0,
    ==> 0,1,1
    ==> LINEAR_SPAN
    ==>
    ==>
    kill HL,c;
    // Note that (1,0,0) and (-1,0,0) form a line, hence also possible:
    intmat HL[3][3]=
    0,1, 1,
    0,1,-1,
    0,0, 1;
    intmat L[1][3]=
    1,0,0;
    cone c=coneViaPoints(HL,L);
    c;
    ==> AMBIENT_DIM
    ==> 3
    ==> FACETS
    ==> 0,1,0,
    ==> 0,1,1
    ==> LINEAR_SPAN
    ==>
    ==>
    kill HL,L,c;
    // lineality space is exactly Lin(1,0,0)
    intmat HL[3][3]=
    0,1, 1,
    0,1,-1,
    0,0, 1;
    intmat L[1][3]=
    1,0,0;
    cone c=coneViaPoints(HL,L,1);
    c;
    ==> AMBIENT_DIM
    ==> 3
    ==> FACETS
    ==> 0,1,0,
    ==> 0,1,1
    ==> LINEAR_SPAN
    ==>
    ==>
    kill HL,L,c;
    // and that (0,1,-1), (0,1,1) generate rays
    intmat HL[3][3]=
    0,1, 1,
    0,1,-1;
    intmat L[1][3]=
    1,0,0;
    cone c=coneViaPoints(HL,L,1);
    c;
    ==> AMBIENT_DIM
    ==> 3
    ==> FACETS
    ==> 0,1,-1,
    ==> 0,1, 1
    ==> LINEAR_SPAN
    ==>
    ==>
    kill HL,L,c;
    // and that (0,1,-1), (0,1,1) generate rays
    intmat HL[3][3]=
    0,1, 1,
    0,1,-1;
    intmat L[1][3]=
    1,0,0;
    cone c=coneViaPoints(HL,L,3);
    c;
    ==> AMBIENT_DIM
    ==> 3
    ==> FACETS
    ==> 0,1,-1,
    ==> 0,1, 1
    ==> LINEAR_SPAN
    ==>
    ==>

User manual for Singular version 4.4.1, 2025, generated by texi2html.