diff --git a/nonlinear/NonlinearOptimization-inl.h b/nonlinear/NonlinearOptimization-inl.h
index 7c0c827f9..660dfdbc3 100644
--- a/nonlinear/NonlinearOptimization-inl.h
+++ b/nonlinear/NonlinearOptimization-inl.h
@@ -55,6 +55,14 @@ namespace gtsam {
 		throw runtime_error("optimizeMultiFrontal: not implemented");
 	}
 
+	/**
+	 * The multifrontal solver
+	 */
+	template<class G, class T>
+	T	optimizeSPCG(const G& graph, const T& initialEstimate, const NonlinearOptimizationParameters& parameters) {
+		throw runtime_error("optimizeSPCG: not implemented");
+	}
+
 	/**
 	 * optimization that returns the values
 	 */
@@ -66,7 +74,10 @@ namespace gtsam {
 			return optimizeElimination<G,T>(graph, initialEstimate, parameters);
 		case MULTIFRONTAL:
 			return optimizeMultiFrontal<G,T>(graph, initialEstimate, parameters);
+		case SPCG:
+			return optimizeSPCG<G,T>(graph, initialEstimate, parameters) ;
 		}
+		throw runtime_error("optimizeSPCG: undefined solver");
 	}
 
 } //namespace gtsam
diff --git a/nonlinear/NonlinearOptimization.h b/nonlinear/NonlinearOptimization.h
index 220f14d24..f0cd9ae39 100644
--- a/nonlinear/NonlinearOptimization.h
+++ b/nonlinear/NonlinearOptimization.h
@@ -36,7 +36,8 @@ namespace gtsam {
 	 */
 	enum LinearSolver{
 		ELIMINATION,      // Elimination
-		MULTIFRONTAL      // Multi-frontal
+		MULTIFRONTAL,      // Multi-frontal
+		SPCG,			  // Subgraph Preconditioned Conjugate Gradient
 	};