Fix segfault of notmpterms option with block decomposition

By the way, ensure that temporary terms associated to external functions are
not removed, since they are not optional.

src/ModelTree.cc

@@ -986,7 +986,7 @@ ModelTree::computeTemporaryTerms(bool is_matlab, bool no_tmp_terms)
 }
 
 void
-ModelTree::computeBlockTemporaryTerms()
+ModelTree::computeBlockTemporaryTerms(bool no_tmp_terms)
 {
   int nb_blocks = blocks.size();
   blocks_temporary_terms.resize(nb_blocks);
@@ -1017,6 +1017,14 @@ ModelTree::computeBlockTemporaryTerms()
       additionalBlockTemporaryTerms(blk, blocks_temporary_terms, reference_count);
     }
 
+  /* If the user has specified the notmpterms option, clear all temporary
+     terms, except those that correspond to external functions (since they are
+     not optional) */
+  if (no_tmp_terms)
+    for (auto &it : blocks_temporary_terms)
+      for (auto &it2 : it)
+        erase_if(it2, [](expr_t e) { return !dynamic_cast<AbstractExternalFunctionNode *>(e); });
+
   // Compute indices in the temporary terms vector
   blocks_temporary_terms_idxs.clear();
   for (int idx{0};
@@ -1977,8 +1985,7 @@ ModelTree::computingPassBlock(const eval_context_t &eval_context, bool no_tmp_te
   printBlockDecomposition();
   computeChainRuleJacobian();
   determineLinearBlocks();
-  if (!no_tmp_terms)
-    computeBlockTemporaryTerms();
+  computeBlockTemporaryTerms(no_tmp_terms);
   block_decomposed = true;
 }
 

src/ModelTree.hh

@@ -247,7 +247,7 @@ protected:
   //! Computes temporary terms (for all equations and derivatives)
   void computeTemporaryTerms(bool is_matlab, bool no_tmp_terms);
   //! Computes temporary terms per block
-  void computeBlockTemporaryTerms();
+  void computeBlockTemporaryTerms(bool no_tmp_terms);
 
 private:
   /* Add additional temporary terms for a given block. This method is called by