| LIB "homolog.lib";
int p = printlevel;
printlevel = 1;
ring r = 0,(x,y),dp;
ideal i = x2,y;
ideal j = x;
list E = Tor(0..2,i,j); // Tor_k(r/i,r/j) for k=0,1,2 over r
→ // dimension of Tor_0: 0
→ // vdim of Tor_0: 1
→
→ // Computing Tor_1 (help Tor; gives an explanation):
→ // Let 0 <- coker(M) <- G0 <-M- G1 be the present. of coker(M),
→ // and 0 <- coker(N) <- F0 <-N- F1 <- F2 <- ... a resolution of
→ // coker(N), then Tensor(G0,F1)-->Tensor(G0,F0) is given by:
→ x
→ // and Tensor(G0,F2) + Tensor(G1,F1)-->Tensor(G0,F1) is given by:
→ 0,x2,y
→
→ // dimension of Tor_1: 0
→ // vdim of Tor_1: 1
→
→ // Computing Tor_2 (help Tor; gives an explanation):
→ // Let 0 <- coker(M) <- G0 <-M- G1 be the present. of coker(M),
→ // and 0 <- coker(N) <- F0 <-N- F1 <- F2 <- ... a resolution of
→ // coker(N), then Tensor(G0,F2)-->Tensor(G0,F1) is given by:
→ 0
→ // and Tensor(G0,F3) + Tensor(G1,F2)-->Tensor(G0,F2) is given by:
→ 1,x2,y
→
→ // dimension of Tor_2: -1
→
qring R = std(i);
ideal j = fetch(r,j);
module M = [x,0],[0,x];
printlevel = 2;
module E1 = Tor(1,M,j); // Tor_1(R^2/M,R/j) over R=r/i
→ // Computing Tor_1 (help Tor; gives an explanation):
→ // Let 0 <- coker(M) <- G0 <-M- G1 be the present. of coker(M),
→ // and 0 <- coker(N) <- F0 <-N- F1 <- F2 <- ... a resolution of
→ // coker(N), then Tensor(G0,F1)-->Tensor(G0,F0) is given by:
→ x,0,
→ 0,x
→ // and Tensor(G0,F2) + Tensor(G1,F1)-->Tensor(G0,F1) is given by:
→ x,0,x,0,
→ 0,x,0,x
→
→ // dimension of Tor_1: 0
→ // vdim of Tor_1: 2
→
list l = Tor(3,M,M,1); // Tor_3(R^2/M,R^2/M) over R=r/i
→ // Computing Tor_3 (help Tor; gives an explanation):
→ // Let 0 <- coker(M) <- G0 <-M- G1 be the present. of coker(M),
→ // and 0 <- coker(N) <- F0 <-N- F1 <- F2 <- ... a resolution of
→ // coker(N), then Tensor(G0,F3)-->Tensor(G0,F2) is given by:
→ x,0,0,0,
→ 0,x,0,0,
→ 0,0,x,0,
→ 0,0,0,x
→ // and Tensor(G0,F4) + Tensor(G1,F3)-->Tensor(G0,F3) is given by:
→ x,0,0,0,x,0,0,0,
→ 0,x,0,0,0,x,0,0,
→ 0,0,x,0,0,0,x,0,
→ 0,0,0,x,0,0,0,x
→
→ // dimension of Tor_3: 0
→ // vdim of Tor_3: 4
→
→ // columns of matrix are kbase of Tor_3 in Tensor(G0,F3)
→ 1,0,0,0,
→ 0,1,0,0,
→ 0,0,1,0,
→ 0,0,0,1
→
printlevel = p;
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