diff --git a/stim/biomodels/cellset.h b/stim/biomodels/cellset.h
index b09935d..e922a0d 100644
--- a/stim/biomodels/cellset.h
+++ b/stim/biomodels/cellset.h
@@ -20,6 +20,22 @@ protected:
 	void init(){
 
 	}
+
+	/// Initialize fields for a standard cell set containing three points and a radius
+	void init_p3(){
+		fields.insert(std::pair<std::string, size_t>("x", 0));
+		ip[0] = 0;
+		fields.insert(std::pair<std::string, size_t>("y", 1));
+		ip[1] = 1;
+		fields.insert(std::pair<std::string, size_t>("z", 2));
+		ip[2] = 2;
+	}
+
+	void init_p3r(){
+		init_p3();
+		fields.insert(std::pair<std::string, size_t>("radius", 3));
+		ip[0] = 3;
+	}
 public:
 	/// Constructor - create an empty cell set
 	cellset(){
@@ -126,6 +142,31 @@ public:
 		return minval;
 	}
 
+	/// adds a cell to the cell set
+	void add(double x, double y, double z, double r = 0){
+
+		if(cells.size() == 0){							//if the cell set is empty
+			if(r == 0)									//if the radius is zero
+				init_p3();								//initialize without a radius
+			else
+				init_p3r();								//otherwise initialize with a radius
+		}
+
+		size_t nf = fields.size();						//get the number of fields
+		size_t bytes = sizeof(double) * nf;				//get the size of a cell field
+		double* newcell = (double*) malloc(bytes);		//allocate memory for the new cell
+		memset(newcell, 0, bytes);						//initialize all fields to zero
+		newcell[ip[0]] = x;
+		newcell[ip[1]] = y;
+		newcell[ip[2]] = z;
+
+		if(r != 0){										//if the user specifies a radius
+			size_t ir = fields["radius"];				//get the index for the radius field
+			newcell[ir] = r;							//add the radius to the field
+		}
+		cells.push_back(newcell);						//push the new memory entry into the cell array
+	}
+
 
 };		//end class cellset
 };		//end namespace stim
--
libgit2 0.21.4