diff --git a/src/sheet07.cpp b/src/sheet07.cpp
index 82db29c..f8b3885 100644
--- a/src/sheet07.cpp
+++ b/src/sheet07.cpp
@@ -1,40 +1,55 @@
 #include <exception>
-#include<iostream>
+#include <iostream>
 #include <ostream>
 #include <system_error>
-#include<vector>
-#include<initializer_list>
-#include<stdexcept>
+#include <vector>
+#include <initializer_list>
+#include <stdexcept>
+#include <type_traits>
+#include <chrono>
 
 template<typename T>
+typename std::enable_if<std::is_arithmetic<T>::value, &operator*>
 class matrix
 {
 	public:
 		matrix(size_t rows, size_t columns) : rows(rows), columns(columns)
 		{
-			data();
+			data = std::vector<T>(rows*columns);
 		}
+
 		matrix(size_t rows, size_t columns, const T &ival) : rows(rows), columns(columns)
 		{
 			data = std::vector<T>(rows*columns, ival);
 		}
+
 		matrix(std::initializer_list<std::initializer_list<T>> imat)
 		{
+			size_t column_num = 0;
+			size_t row_num = 0;
 			size_t prev_length;
+			bool isNotFirst = false;
 			for(std::initializer_list<T> row : imat)
 			{
-				if(prev_length!=row.size())
+				if(isNotFirst&&prev_length!=row.size())
 				{
-					throw std::domain_error("provided initializer list with empty spots.");
+					throw std::domain_error("provided initializer list with empty elements.");
 				}
 
+				++row_num;
 				prev_length = row.size();
 
+
 				for(T t : row)
 				{
+					if(!isNotFirst) { ++column_num; }
 					data.push_back(t);
 				}
+				isNotFirst = true;
 			}
+
+			this->rows = row_num;
+			this->columns = column_num;
 		}
 		T& operator() (size_t row, size_t column)
 		{
@@ -67,8 +82,51 @@ class matrix
 		size_t num_rows() const noexcept { return rows; }
 		size_t num_columns() const noexcept { return columns; }
 
+		std::vector<T> column_to_vec(size_t column) const
+		{
+			std::vector<T> out(this->num_rows());
+
+			for(size_t i=0; i<this->num_rows();++i)
+			{
+				out.push_back((*this)(i,column));
+			}
+			return out;
+		}
+
+		std::vector<T> row_to_vec(size_t row) const
+		{
+			std::vector<T> out(this->num_columns());
+
+			for(size_t i=0; i<this->num_columns();++i)
+			{
+				out.push_back((*this)(row,i));
+			}
+			return out;
+		}
+
+		static T dot_product(std::vector<T> lhs, std::vector<T> rhs)
+		{
+			if(lhs.size()!=rhs.size())
+			{
+				throw std::domain_error("vectors must be the same size");
+			}
+
+			T sum = 0;
+
+			for(size_t i=0; i<lhs.size(); ++i)
+			{
+				sum += lhs.at(i)*rhs.at(i);
+			}
+			return sum;			
+		}
+
 		friend matrix operator* (const matrix &lhs, const T &scale)
 		{
+			if(!std::is_arithmetic<T>())
+			{
+				throw std::domain_error("type must be arithmetic.");
+			}
+
 			matrix out(lhs.num_rows(), lhs.num_columns(), 0);
 			for(size_t x=0; x<lhs.num_columns(); ++x)
 			{
@@ -80,10 +138,25 @@ class matrix
 			return out;
 		}
 
+		typename std::enable_if<std::is_arithmetic<T>::value>
+		friend matrix operator* (const matrix &lhs, const matrix &rhs) = delete;
+
 		friend matrix operator* (const matrix &lhs, const matrix &rhs)
 		{
-			//TODO
-			throw std::logic_error("unimplemented");
+			if(!std::is_arithmetic<T>())
+			{
+				throw std::domain_error("type must be arithmetic.");
+			}
+
+			if(lhs.num_columns()!=rhs.num_rws(rows), columns(columns)
+		{
+				for(size_t y=0; y<out.num_rows(); ++y)
+				{
+					out(y,x)=dot_product(lhs.row_to_vec(y), rhs.column_to_vec(x));
+				}
+			}
+			
+			return out;
 		}
 
 		friend bool operator== (const matrix &lhs, const matrix &rhs)
@@ -113,9 +186,9 @@ class matrix
 
 		friend std::ostream& operator<< (std::ostream &os, const matrix &m)
 		{
-			for(size_t x=0; x<m.num_columns(); ++x)
+			for(size_t y=0; y<m.num_rows(); ++y)
 			{
-				for(size_t y=0; y<m.num_rows(); ++y)
+				for(size_t x=0; x<m.num_columns(); ++x)
 				{
 					os << m(y,x) << '\t';
 				}
@@ -132,8 +205,36 @@ class matrix
 
 int main()
 {
-	matrix<int> m(5,5,5);
-	std::cout << m;
-	std::cout << m*5;
-	std::cout << m*m;
+  // // TODO comment-in the following code as needed to test your implementation
+  // // above.
+  matrix<double> a(3, 3, 3);
+  a = a * 2;
+  matrix<double> b(3, 3, 4);
+  auto start = std::chrono::steady_clock::now();
+  matrix<double> c = a * b;
+  auto end = std::chrono::steady_clock::now();
+  auto duration =
+      std::chrono::duration_cast<std::chrono::nanoseconds>(end - start).count();
+  std::cout << "multiplied a:\n";
+  std::cout << a << '\n';
+  std::cout << "with b:\n";
+  std::cout << b << '\n';
+  std::cout << "in " << duration << "ns\n";
+  std::cout << "result is:\n";
+  std::cout << c << '\n';
+
+  matrix<double> d = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
+  matrix<double> e = {{9, 8, 7}, {6, 5, 4}, {3, 2, 1}};
+  start = std::chrono::steady_clock::now();
+  matrix<double> f = d * e;
+  end = std::chrono::steady_clock::now();
+  duration =
+      std::chrono::duration_cast<std::chrono::nanoseconds>(end - start).count();
+  std::cout << "multiplied d:\n";
+  std::cout << d << '\n';
+  std::cout << "with e:\n";
+  std::cout << e << '\n';
+  std::cout << "in " << duration << "ns\n";
+  std::cout << "result is:\n";
+  std::cout << f << '\n';
 }
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