From d4b924cc637855953df16ea8d6bc79f9329f11d6 Mon Sep 17 00:00:00 2001
From: Dominik Kamp <dominik.kamp@uni-bayreuth.de>
Date: Tue, 2 Apr 2024 15:29:18 +0200
Subject: [PATCH] Resolve "Assertion triggered by !3354"

---
 CHANGELOG                |  2 ++
 src/scip/cons_logicor.c  |  2 +-
 src/scip/cons_setppc.c   |  2 +-
 src/scip/cons_varbound.c |  2 +-
 src/scip/matrix.c        | 39 +++++++++++++++++++++++++++++++++++----
 5 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 32be2eb8c7..d89e59b983 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,8 @@ Fixed bugs
 - declare contradicting infinities in getMinActivity() and getMaxActivity() as non-tight
 - reject farkas solution with large values to bound magnification of errors in SCIPgetFarkasProof()
 - if all variables are fixed, apply relative feasibility tolerance to avoid invalid infeasibility in applyFixings() of cons_linear.c
+- delete empty redundant knapsack and linear constraints after cleanup in SCIPmatrixCreate()
+- cleanup first constraints in SCIPcleanupConssVarbound(), SCIPcleanupConssSetppc(), and SCIPcleanupConssLogicor()
 
 Miscellaneous
 -------------
diff --git a/src/scip/cons_logicor.c b/src/scip/cons_logicor.c
index ebaed51f43..3cc0e3c1d1 100644
--- a/src/scip/cons_logicor.c
+++ b/src/scip/cons_logicor.c
@@ -5684,7 +5684,7 @@ SCIP_RETCODE SCIPcleanupConssLogicor(
    SCIP_CALL( SCIPallocBufferArray(scip, &entries, nentries) );
 
    /* loop backwards since then deleted constraints do not interfere with the loop */
-   for( i = nconss - 1; i > 0; --i )
+   for( i = nconss - 1; i >= 0; --i )
    {
       SCIP_CONS* cons;
       SCIP_Bool redundant;
diff --git a/src/scip/cons_setppc.c b/src/scip/cons_setppc.c
index c170719a5d..96a087bc20 100644
--- a/src/scip/cons_setppc.c
+++ b/src/scip/cons_setppc.c
@@ -9763,7 +9763,7 @@ SCIP_RETCODE SCIPcleanupConssSetppc(
    conss = onlychecked ? SCIPconshdlrGetCheckConss(conshdlr) : SCIPconshdlrGetConss(conshdlr);
 
    /* loop backwards since then deleted constraints do not interfere with the loop */
-   for( i = nconss - 1; i > 0; --i )
+   for( i = nconss - 1; i >= 0; --i )
    {
       SCIP_CONS* cons = conss[i];
 
diff --git a/src/scip/cons_varbound.c b/src/scip/cons_varbound.c
index ac462bb692..58576af316 100644
--- a/src/scip/cons_varbound.c
+++ b/src/scip/cons_varbound.c
@@ -5702,7 +5702,7 @@ SCIP_RETCODE SCIPcleanupConssVarbound(
    conss = onlychecked ? SCIPconshdlrGetCheckConss(conshdlr) : SCIPconshdlrGetConss(conshdlr);
 
    /* loop backwards since then deleted constraints do not interfere with the loop */
-   for( i = nconss - 1; i > 0; --i )
+   for( i = nconss - 1; i >= 0; --i )
    {
       SCIP_CALL( applyFixings(scip, conss[i], eventhdlr, infeasible, nchgbds, ndelconss, naddconss) );
 
diff --git a/src/scip/matrix.c b/src/scip/matrix.c
index 66d8127290..a9d1080e09 100644
--- a/src/scip/matrix.c
+++ b/src/scip/matrix.c
@@ -467,11 +467,14 @@ SCIP_RETCODE SCIPmatrixCreate(
 {
    SCIP_MATRIX* matrix;
    SCIP_CONSHDLR** conshdlrs;
+   SCIP_CONSHDLR* conshdlr;
    const char* conshdlrname;
    SCIP_Bool stopped;
    SCIP_VAR** vars;
    SCIP_VAR* var;
+   SCIP_CONS** conshdlrconss;
    SCIP_CONS* cons;
+   int nconshdlrconss;
    int nconshdlrs;
    int nconss;
    int nconssall;
@@ -509,8 +512,6 @@ SCIP_RETCODE SCIPmatrixCreate(
 
    for( i = 0; i < nconshdlrs; ++i )
    {
-      int nconshdlrconss;
-
       nconshdlrconss = SCIPconshdlrGetNCheckConss(conshdlrs[i]);
 
       if( nconshdlrconss > 0 )
@@ -586,10 +587,42 @@ SCIP_RETCODE SCIPmatrixCreate(
    if( *infeasible )
       return SCIP_OKAY;
 
+   /* delete empty redundant knapsack constraints */
+   conshdlr = SCIPfindConshdlr(scip, "knapsack");
+   if( conshdlr != NULL )
+   {
+      nconshdlrconss = SCIPconshdlrGetNCheckConss(conshdlr);
+      conshdlrconss = SCIPconshdlrGetCheckConss(conshdlr);
+      for( i = nconshdlrconss - 1; i >= 0; --i )
+      {
+         if( SCIPgetNVarsKnapsack(scip, conshdlrconss[i]) == 0 )
+         {
+            SCIP_CALL( SCIPdelCons(scip, conshdlrconss[i]) );
+            ++(*ndelconss);
+         }
+      }
+   }
+
    SCIP_CALL( SCIPcleanupConssLinear(scip, TRUE, infeasible) );
    if( *infeasible )
       return SCIP_OKAY;
 
+   /* delete empty redundant linear constraints */
+   conshdlr = SCIPfindConshdlr(scip, "linear");
+   if( conshdlr != NULL )
+   {
+      nconshdlrconss = SCIPconshdlrGetNCheckConss(conshdlr);
+      conshdlrconss = SCIPconshdlrGetCheckConss(conshdlr);
+      for( i = nconshdlrconss - 1; i >= 0; --i )
+      {
+         if( SCIPgetNVarsLinear(scip, conshdlrconss[i]) == 0 )
+         {
+            SCIP_CALL( SCIPdelCons(scip, conshdlrconss[i]) );
+            ++(*ndelconss);
+         }
+      }
+   }
+
    vars = SCIPgetVars(scip);
    nvars = SCIPgetNVars(scip);
 
@@ -661,8 +694,6 @@ SCIP_RETCODE SCIPmatrixCreate(
    /* loop a second time over constraints handlers and add supported constraints to the matrix */
    for( i = 0; i < nconshdlrs; ++i )
    {
-      SCIP_CONS** conshdlrconss;
-      int nconshdlrconss;
       SCIP_Bool rowadded;
 
       if( SCIPisStopped(scip) || (onlyifcomplete && !(*complete)) )