From 1eb6fc22854af71f70744e31265eaf2e1bbb2c59 Mon Sep 17 00:00:00 2001
From: Alessio Quaglino <quaglino@google.com>
Date: Wed, 25 Sep 2024 02:55:05 -0700
Subject: [PATCH] Disallow using elasticity and edge constraints at the same
 time.

Fixes #2084.

PiperOrigin-RevId: 678614880
Change-Id: I44eead3dc4edf82d725a3063b927a421c660721a
---
 src/user/user_mesh.cc        | 3 +++
 src/xml/xml_native_reader.cc | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/src/user/user_mesh.cc b/src/user/user_mesh.cc
index cb1d5c0a..d03fc42b 100644
--- a/src/user/user_mesh.cc
+++ b/src/user/user_mesh.cc
@@ -2896,6 +2896,9 @@ void mjCFlex::Compile(const mjVFS* vfs) {
 
   // compute elasticity
   if (young > 0) {
+    if (poisson < 0 || poisson >= 0.5) {
+      throw mjCError(this, "Poisson ratio must be in [0, 0.5)");
+    }
     stiffness.assign(21*nelem, 0);
     for (unsigned int t = 0; t < nelem; t++) {
       if (dim==2) {
diff --git a/src/xml/xml_native_reader.cc b/src/xml/xml_native_reader.cc
index d5813799..5fcaf155 100644
--- a/src/xml/xml_native_reader.cc
+++ b/src/xml/xml_native_reader.cc
@@ -2694,6 +2694,11 @@ void mjXReader::OneFlexcomp(XMLElement* elem, mjsBody* body, const mjVFS* vfs) {
     ReadAttr(elasticity, "thickness", 1, &dflex.thickness, text);
   }
 
+  // check errors
+  if (elasticity && fcomp.equality) {
+    throw mjXError(elem, "elasticity and edge constraints cannot both be present");
+  }
+
   // contact
   XMLElement* cont = FirstChildElement(elem, "contact");
   if (cont) {