new option noopac, don't do op simulation before ac if circuit is linear

May simplify ac simulation of passive RLC networks
(No need to add series resistors in Ls, allows to C inseries)

src/frontend/inp.c

@@ -10,6 +10,7 @@ Author: 1985 Wayne A. Christopher
 
 #include "ngspice/ngspice.h"
 
+#include "ngspice/cktdefs.h"
 #include "ngspice/cpdefs.h"
 #include "ngspice/inpdefs.h"
 #include "ngspice/ftedefs.h"
@@ -49,6 +50,7 @@ static char *upper(register char *string);
 static bool doedit(char *filename);
 static struct line *com_options = NULL;
 static void consaves(wordlist *wl);
+static void cktislinear(CKTcircuit *ckt, struct line *deck);
 
 void line_free_x(struct line *deck, bool recurse);
 
@@ -796,6 +798,7 @@ inp_dodeck(
         ckt = NULL;
     }
 
+    cktislinear(ckt, deck);
     out_init();
 
     ft_curckt->FTEstats->FTESTATdeckNumLines = 0;
@@ -1138,3 +1141,40 @@ consaves(wordlist *wl_control)
 
     com_save(wl);
 }
+
+
+/* check the input deck (after inpcom and numparam extensions)
+   for linear elements. If only linear elements are found,
+   ckt->CKTisLinear is set to 1. Return immediately if a first
+   non-linear element is found. */
+static void
+cktislinear(CKTcircuit *ckt, struct line *deck)
+{
+    struct line *dd;
+    char firstchar;
+
+    if (deck->li_next)
+        for (dd = deck->li_next; dd; dd = dd->li_next) {
+            firstchar = *dd->li_line;
+            switch (firstchar) {
+                case 'r':
+                case 'l':
+                case 'c':
+                case 'i':
+                case 'v':
+                case '*':
+                case '.':
+                case 'e':
+                case 'g':
+                case 'f':
+                case 'h':
+                    continue;
+                    break;
+                default:
+                    ckt->CKTisLinear = 0;
+                    return;
+            }
+        }
+
+    ckt->CKTisLinear = 1;
+}

src/include/ngspice/cktdefs.h

@@ -275,7 +275,10 @@ struct CKTcircuit {
     int CKTsc_iter;
 /* SP: 100609 */
 #endif
-
+    unsigned int CKTisLinear:1; /* flag to indicate that the circuit
+                                   contains only linear elements */
+    unsigned int CKTnoopac:1; /* flag to indicate that OP will not be evaluated
+                                 during AC simulation */
 };
 
 

src/include/ngspice/optdefs.h

@@ -124,6 +124,8 @@ typedef struct {
 #define OPT_ABSDV        66  /* Original: 51 (Node_Damping) */ 
 #define OPT_RELDV        67  /* Original: 52 (Node_Damping) */
 
+#define OPT_NOOPAC       68
+
 #ifdef XSPICE
 /* gtri - begin - wbk - add new options */
 #define OPT_ENH_NOOPALTER           100

src/include/ngspice/tskdefs.h

@@ -65,6 +65,7 @@ struct TSKtask {
     unsigned int TSKnodeDamping:1;  /* flag for node damping */
     double TSKabsDv;                 /* abs limit for iter-iter voltage change */
     double TSKrelDv;                 /* rel limit for iter-iter voltage change */
+    unsigned int TSKnoopac:1; /* flag for no OP calculation before AC */
 };
 
 #endif /*TSK*/

src/spicelib/analysis/acan.c

@@ -123,17 +123,21 @@ ACan(CKTcircuit *ckt, int restart)
     }
     else 
 #endif 
-/* If no event-driven instances, do what SPICE normally does */
-    error = CKTop(ckt,
-        (ckt->CKTmode & MODEUIC) | MODEDCOP | MODEINITJCT,
-        (ckt->CKTmode & MODEUIC) | MODEDCOP | MODEINITFLOAT,
-        ckt->CKTdcMaxIter);
-
-    if(error){
-        fprintf(stdout,"\nAC operating point failed -\n");
-        CKTncDump(ckt);
-        return(error);
-    } 
+    /* If no event-driven instances, do what SPICE normally does */
+    if (!ckt->CKTnoopac) { /* skip OP if option NOOPAC is set and circuit is linear */
+        error = CKTop(ckt,
+            (ckt->CKTmode & MODEUIC) | MODEDCOP | MODEINITJCT,
+            (ckt->CKTmode & MODEUIC) | MODEDCOP | MODEINITFLOAT,
+            ckt->CKTdcMaxIter);
+
+        if(error){
+            fprintf(stdout,"\nAC operating point failed -\n");
+            CKTncDump(ckt);
+            return(error);
+        }
+    }
+    else
+        fprintf(stdout,"\n Linear circuit, option noopac given: no OP analysis\n");
 		
 #ifdef XSPICE
 /* gtri - add - wbk - 12/19/90 - Add IPC stuff */

src/spicelib/analysis/cktdojob.c

@@ -103,6 +103,7 @@ CKTdoJob(CKTcircuit *ckt, int reset, TSKtask *task)
     ckt->CKTrelDv = task->TSKrelDv;
     ckt->CKTtroubleNode  = 0;
     ckt->CKTtroubleElt  = NULL;
+    ckt->CKTnoopac = task->TSKnoopac && ckt->CKTisLinear;
 #ifdef NEWTRUNC
     ckt->CKTlteReltol = task->TSKlteReltol;
     ckt->CKTlteAbstol = task->TSKlteAbstol;

src/spicelib/analysis/cktntask.c

@@ -70,6 +70,7 @@ CKTnewTask(CKTcircuit *ckt, TSKtask **taskPtr, IFuid taskName, TSKtask **defPtr)
         tsk->TSKnodeDamping     = def->TSKnodeDamping;
         tsk->TSKabsDv           = def->TSKabsDv;
         tsk->TSKrelDv           = def->TSKrelDv;
+        tsk->TSKnoopac          = def->TSKnoopac;
 #ifdef NEWTRUNC
         tsk->TSKlteReltol       = def->TSKlteReltol;
         tsk->TSKlteAbstol       = def->TSKlteAbstol;

src/spicelib/analysis/cktsopt.c

@@ -158,6 +158,9 @@ CKTsetOpt(CKTcircuit *ckt, JOB *anal, int opt, IFvalue *val)
     case OPT_RELDV:
         task->TSKrelDv = val->rValue;
         break;
+    case OPT_NOOPAC:
+        task->TSKnoopac = (val->iValue != 0);
+        break;
 /* gtri - begin - wbk - add new options */
 #ifdef XSPICE
     case OPT_EVT_MAX_OP_ALTER:
@@ -311,7 +314,9 @@ static IFparm OPTtbl[] = {
  { "absdv", OPT_ABSDV, IF_SET|IF_REAL,
         "Maximum absolute iter-iter node voltage change" },
  { "reldv", OPT_RELDV, IF_SET|IF_REAL,
-        "Maximum relative iter-iter node voltage change" }
+        "Maximum relative iter-iter node voltage change" },
+ { "noopac", OPT_NOOPAC, IF_SET|IF_FLAG,
+        "No op calculation in ac if circuit is linear" }
 };
 
 int OPTcount = NUMELEMS(OPTtbl);