Reformat and add some adjoint gradient

src/sphSmooth.hpp

@@ -79,14 +79,30 @@ namespace CosmoTool {
       return internal.currentCenter;
     }
 
+    /** This is the pure SPH smoothing function. It does not reweight by the
+     * value computed at each grid site.
+     */
     template <typename FuncT>
     ComputePrecision computeSmoothedValue(
         const typename SPHTree::coords &c, FuncT fun, SPHState *state = 0);
 
+    /** This is the weighted SPH smoothing function. It does reweight by the
+     * value computed at each grid site. This ensures the total sum of the interpolated
+     * quantity is preserved by interpolating to the target mesh.
+     */
     template <typename FuncT>
     ComputePrecision computeInterpolatedValue(
         const typename SPHTree::coords &c, FuncT fun, SPHState *state = 0);
 
+    /** This is the adjoint gradient of computeInterpolatedValue w.r.t. to the value
+     * array. FuncT is expected to have the following prototype:
+     *    void((CellValue defined by the user), ComputePrecision weighted_ag_value)
+     */
+    template <typename FuncT>
+    void computeAdjointGradientSmoothedValue(
+        const typename SPHTree::coords &c, ComputePrecision ag_value, FuncT fun,
+        SPHState *state = 0);
+
     ComputePrecision
     getMaxDistance(const typename SPHTree::coords &c, SPHNode *node) const;