Error umpfack umfpack_di_numeric status 1

General Discussion
1

I have the following code:

 //---------------------------------------------------Solving for etaf

  varf ahKf(etafK, varphi)
    =  int2d(Th[K])(kappa*grad(etafK)'*grad(varphi));

  varf fhKf(etafK, varphi)
    = int2d(Th[K])(f*varphi); 

  varf bhKf(vf, varphi)
    = int2d(Th[K])(vf*varphi);
 
  // local matrices for etaf
  matrix Akf = ahKf(VhK,VhK);
  matrix Bkf = bhKf(V0,VhK);
  real[int] Fkf(ndofVhK);
  Fkf = fhKf(0, VhK);

  // block matrix LHS
  matrix AAkf = [ [ Akf, Bkf ],
                  [ Bkf', 0  ] ];

  real[int] rhsetaf(ndofVhK+nDoFu0), soletafk(ndofVhK+nDoFu0);
  real[int] blmf(nDoFu0), lmf(nDoFu0);

  //second equation to hybrid form equal 0
  blmf = 0;

  // block vector RHS
  rhsetaf = [ Fkf, blmf ];

  set(AAkf, solver=sparsesolver);
  soletafk = AAkf^-1*rhsetaf; //solve linear system

  [etafK[], lmf] = soletafk;   //set the value

  cout << "etaF elem " << K << ": " << etafK[] << "\n";

but it keeps giving me the following error:

 Error umpfack umfpack_di_numeric  status  1
 Error umfpack_di_solve  status  1
etaF elem 0: 6	
	-0.3611303349	-0.3611303349	-0.09386227966	-0.09386227966	0.1877245593
	-0.251181056

I already tried to change the solver to

set(AAkf,solver="UMFPACK64")

but the error remains. Does anyone have any ideia what it could be?

2

Remark, in new version (develop) the error stop FreeFEM and the error 1 is

            case 1:
                cout << status<< " UMFPACK WARNING singular matrix " <<endl;
                break;
3

In this code, I used the following code to build a local mesh

 real[int, int] nodes = [[coordX0, coordY0], [coordX1,coordY1],
                          [coordX2, coordY2]];

 //cout << nodes << "\n";

 border f0(t=0,1){P.x=nodes(1,0)*t + nodes(0,0)*(1-t);P.y=nodes(1,1)*t + nodes(0,1)*(1-t); label=1;};
 border f1(t=0,1){P.x=nodes(2,0)*t + nodes(1,0)*(1-t);P.y=nodes(2,1)*t + nodes(1,1)*(1-t); label=2;};
 border f2(t=0,1){P.x=nodes(0,0)*t + nodes(2,0)*(1-t);P.y=nodes(0,1)*t + nodes(2,1)*(1-t); label=3;};
 
 Th[K] = buildmesh(f0(localh) + f1(localh) + f2(localh), fixedborder=true);

I don’t know if its related, but for etaF I should have only one value, instead I’m getting a vector of values as you can see above. Perhaps you could help me with this?