diff --git a/gtsam/linear/SubgraphPreconditioner.cpp b/gtsam/linear/SubgraphPreconditioner.cpp
index 80adfc098..657846f95 100644
--- a/gtsam/linear/SubgraphPreconditioner.cpp
+++ b/gtsam/linear/SubgraphPreconditioner.cpp
@@ -587,25 +587,22 @@ void SubgraphPreconditioner::print(const std::string& s) const {
 
 /*****************************************************************************/
 void SubgraphPreconditioner::solve(const Vector &y, Vector &x) const {
-  /* copy first */
   assert(x.size() == y.size());
-  std::copy(y.data(), y.data() + y.rows(), x.data());
 
-  /* in place back substitute */
+  /* back substitute */
   for (const auto &cg : boost::adaptors::reverse(*Rc1_)) {
     /* collect a subvector of x that consists of the parents of cg (S) */
-    const Vector xParent = getSubvector(
-        x, keyInfo_, KeyVector(cg->beginParents(), cg->endParents()));
-    const Vector rhsFrontal = getSubvector(
-        x, keyInfo_, KeyVector(cg->beginFrontals(), cg->endFrontals()));
+    const KeyVector parentKeys(cg->beginParents(), cg->endParents());
+    const KeyVector frontalKeys(cg->beginFrontals(), cg->endFrontals());
+    const Vector xParent = getSubvector(x, keyInfo_, parentKeys);
+    const Vector rhsFrontal = getSubvector(y, keyInfo_, frontalKeys);
 
     /* compute the solution for the current pivot */
     const Vector solFrontal = cg->get_R().triangularView<Eigen::Upper>().solve(
         rhsFrontal - cg->get_S() * xParent);
 
     /* assign subvector of sol to the frontal variables */
-    setSubvector(solFrontal, keyInfo_,
-                 KeyVector(cg->beginFrontals(), cg->endFrontals()), x);
+    setSubvector(solFrontal, keyInfo_, frontalKeys, x);
   }
 }
 
@@ -657,25 +654,24 @@ void SubgraphPreconditioner::build(const GaussianFactorGraph &gfg, const KeyInfo
 }
 
 /*****************************************************************************/
-Vector getSubvector(const Vector &src, const KeyInfo &keyInfo, const KeyVector &keys) {
-
+Vector getSubvector(const Vector &src, const KeyInfo &keyInfo,
+                    const KeyVector &keys) {
   /* a cache of starting index and dim */
-  typedef vector<std::pair<size_t, size_t> > Cache;
-  Cache cache;
+  vector<std::pair<size_t, size_t> > cache;
 
   /* figure out dimension by traversing the keys */
-  size_t d = 0;
-  for ( const Key &key: keys ) {
+  size_t dim = 0;
+  for (const Key &key : keys) {
     const KeyInfoEntry &entry = keyInfo.find(key)->second;
     cache.emplace_back(entry.colstart(), entry.dim());
-    d += entry.dim();
+    dim += entry.dim();
   }
 
   /* use the cache to fill the result */
-  Vector result = Vector::Zero(d, 1);
+  Vector result = Vector::Zero(dim);
   size_t idx = 0;
-  for ( const Cache::value_type &p: cache ) {
-    result.segment(idx, p.second) = src.segment(p.first, p.second) ;
+  for (const auto &p : cache) {
+    result.segment(idx, p.second) = src.segment(p.first, p.second);
     idx += p.second;
   }
 
@@ -684,7 +680,6 @@ Vector getSubvector(const Vector &src, const KeyInfo &keyInfo, const KeyVector &
 
 /*****************************************************************************/
 void setSubvector(const Vector &src, const KeyInfo &keyInfo, const KeyVector &keys, Vector &dst) {
-  /* use the cache  */
   size_t idx = 0;
   for ( const Key &key: keys ) {
     const KeyInfoEntry &entry = keyInfo.find(key)->second;
diff --git a/gtsam/linear/SubgraphPreconditioner.h b/gtsam/linear/SubgraphPreconditioner.h
index 6bba3dd1c..a9746d104 100644
--- a/gtsam/linear/SubgraphPreconditioner.h
+++ b/gtsam/linear/SubgraphPreconditioner.h
@@ -249,8 +249,8 @@ namespace gtsam {
 
     /* A zero VectorValues with the structure of xbar */
     VectorValues zero() const {
-      VectorValues V(VectorValues::Zero(*xbar_));
-      return V ;
+      assert(xbar_);
+      return VectorValues::Zero(*xbar_);
     }
 
     /**