From 3e3325ad28c12a43c5fcd61f5d53eaf2e7e75ffd Mon Sep 17 00:00:00 2001
From: Marc Pfetsch <pfetsch@mathematik.tu-darmstadt.de>
Date: Mon, 18 Dec 2023 11:49:23 +0100
Subject: [PATCH] allow to skip '*' between number and variable when parsing
 expr

- handle the no-asterisk case as if there was one if number if followed
  by '<'
---
 CHANGELOG            |  3 +++
 src/scip/scip_expr.c | 21 +++++++++++++++------
 src/scip/scip_expr.h |  2 +-
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 1bcfe521cb..05ab1e084c 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -38,6 +38,9 @@ Features
 - added a new separator sepa_lagromory to generate Lagromory cuts in a relax-and-cut framework, i.e., GMI cuts generated
   at different bases that are explored in the process of solving the Lagrangian dual problem at a node. This separator
   is OFF by default.
+- when parsing nonlinear constraints from CIP files, the * after the number in a term is now optional if followed by a variable,
+  i.e., instead of 3*<x>*<y>, now also 3<x>*<y> can be read, but 3<x><y> is not supported;
+  this allows to read some CIP files that were written with SCIP < 8
 
 Performance improvements
 ------------------------
diff --git a/src/scip/scip_expr.c b/src/scip/scip_expr.c
index 1f3a8aa824..461dd214ec 100644
--- a/src/scip/scip_expr.c
+++ b/src/scip/scip_expr.c
@@ -574,19 +574,28 @@ SCIP_RETCODE parseExpr(
          {
             SCIP_CALL( SCIPskipSpace((char**)newpos) );
 
-            if( **newpos != '*' )
+            if( **newpos == '<' )
             {
-               /* no '*', so fall back to parsing term after sign */
-               coef = (*expr == '+') ? 1.0 : -1.0;
-               ++expr;
+               /* found variable name ('*' is considered optional);
+                * keep coefficient in coef and continue parsing term after coefficient
+                */
+               expr = *newpos;
+
+               SCIP_CALL( SCIPskipSpace((char**)&expr) );
             }
-            else
+            else if( **newpos == '*' )
             {
                /* keep coefficient in coef and continue parsing term after coefficient */
                expr = (*newpos)+1;
 
                SCIP_CALL( SCIPskipSpace((char**)&expr) );
             }
+            else
+            {
+               /* term consists of single value; let parseTerm() below parse it */
+               coef = (*expr == '+') ? 1.0 : -1.0;
+               ++expr;
+            }
          }
          else
          {
@@ -1358,7 +1367,7 @@ SCIP_RETCODE SCIPcopyExpr(
  *
  * The actual definition:
  * <pre>
- * Expression -> ["+" | "-"] Term { ("+" | "-" | "number *") ] Term }
+ * Expression -> ["+" | "-"] Term { [ ("+" | "-" | "number *") Term | ("number" <varname>) ] }
  * Term       -> Factor { ("*" | "/" ) Factor }
  * Factor     -> Base [ "^" "number" | "^(" "number" ")" ]
  * Base       -> "number" | "<varname>" | "(" Expression ")" | Op "(" OpExpression ")
diff --git a/src/scip/scip_expr.h b/src/scip/scip_expr.h
index 43bef970ca..93fdc0ed86 100644
--- a/src/scip/scip_expr.h
+++ b/src/scip/scip_expr.h
@@ -277,7 +277,7 @@ SCIP_RETCODE SCIPcopyExpr(
  *
  * The actual definition:
  * <pre>
- * Expression -> ["+" | "-"] Term { ("+" | "-" | "number *") ] Term }
+ * Expression -> ["+" | "-"] Term { [ ("+" | "-" | "number *") Term | ("number" <varname>) ] }
  * Term       -> Factor { ("*" | "/" ) Factor }
  * Factor     -> Base [ "^" "number" | "^(" "number" ")" ]
  * Base       -> "number" | "<varname>" | "(" Expression ")" | Op "(" OpExpression ")