Added a comment in NIiter

src/maths/ni/niiter.c

@@ -146,6 +146,13 @@ NIiter(CKTcircuit *ckt, int maxIter)
 
 #ifdef KLU
                 if (error == E_SINGULAR) {
+
+                    /* Francesco Lannutti - 25 Aug 2020
+                     * If the matrix is numerically singular during ReFactorization, take the same matrix and factor it from scratch in the same iteration.
+                     * This is my mod with KLU. It saves run-time, but also the system at the next iteration may be different.
+                     * How do we guarantee that the system is the same at the next iteration? So, the original SPARSE version below sounds like a bug.
+                     */
+
                     fprintf (stderr, "Warning: KLU ReFactor failed. Factoring again...\n") ;
                     ckt->CKTniState |= NISHOULDREORDER;
                     error = SMPreorder(ckt->CKTmatrix, ckt->CKTpivotAbsTol, ckt->CKTpivotRelTol, ckt->CKTdiagGmin);
@@ -168,6 +175,12 @@ NIiter(CKTcircuit *ckt, int maxIter)
 #else
                 if (error) {
                     if (error == E_SINGULAR) {
+
+                        /* Francesco Lannutti - 25 Aug 2020
+                         * If the matrix is numerically singular during ReFactorization, factor it from scratch at the next iteration.
+                         * This is the original SPICE3F5 code and uses SPARSE.
+                         */
+
                         ckt->CKTniState |= NISHOULDREORDER;
                         DEBUGMSG(" forced reordering....\n");
                         continue;