Sparse 1.3 is the matrix solver if no option (sparse or klu) is given.

KLU is selected by 'option klu'
If both 'option klu' and 'option sparse' are given,
the last one executed determines the solver.
'option sparse=0' de-selects spares, i.e. selects klu.
'option klu=0' de-selects klu, selects sparse.
'option klu=1' has the same meaning as 'option klu'.
'option sparse=1' has the same meaning as 'option sparse'.

src/include/ngspice/optdefs.h

@@ -124,6 +124,7 @@ enum {
 
 #ifdef KLU
     OPT_SPARSE,
+    OPT_KLU,
     OPT_KLU_MEMGROW_FACTOR,
 #endif
 

src/spicelib/analysis/cktntask.c

@@ -141,7 +141,7 @@ CKTnewTask(CKTcircuit *ckt, TSKtask **taskPtr, IFuid taskName, TSKtask **defPtr)
         tsk->TSKepsmin          = 1e-28;
 
 #ifdef KLU
-        tsk->TSKkluMODE         = CKTkluON;
+        tsk->TSKkluMODE         = CKTkluOFF;
         tsk->TSKkluMemGrowFactor = 1.2 ;
 #endif
 

src/spicelib/analysis/cktsopt.c

@@ -180,7 +180,9 @@ CKTsetOpt(CKTcircuit *ckt, JOB *anal, int opt, IFvalue *val)
     case OPT_SPARSE:
         task->TSKkluMODE = (val->iValue == 0);
         break;
-
+    case OPT_KLU:
+        task->TSKkluMODE = (val->iValue != 0);
+        break;
     case OPT_KLU_MEMGROW_FACTOR:
         task->TSKkluMemGrowFactor = (val->rValue == 1.2);
         break;
@@ -348,6 +350,8 @@ static IFparm OPTtbl[] = {
 #ifdef KLU
  { "sparse", OPT_SPARSE, IF_SET|IF_FLAG,
         "Set SPARSE 1.3 as Direct Linear Solver" },
+ { "klu", OPT_KLU, IF_SET|IF_FLAG,
+        "Set KLU as Direct Linear Solver" },
  { "klu_memgrow_factor", OPT_KLU_MEMGROW_FACTOR, IF_SET|IF_REAL,
         "KLU Memory Grow Factor (default is 1.2)" }
 #endif