hw2: preparing for submission

hw2/assignment2.m

@@ -31,6 +31,61 @@ end
 
 loglog(h, err)
 
+%% Problem 6
+
+n = 3000;
+A = rand(n,n);
+B = rand(n,n);
+tic
+[C] = matTimesMat_classical(A, B); 
+toc
+norm(C - A * B) / norm(C) 
+tic
+[C] = matTimesMat_column(A, B); 
+toc
+norm(C - A * B) / norm(C)
+tic
+[C] = matTimesMat_outerProd(A, B); 
+toc
+norm(C - A * B) / norm(C)
+
+%% Problem 3 (functions)
+
 function approx = my_diff(f, x, x_0, h)
     approx = (subs(f,x,x_0 + h) - subs(f, x, x_0)) / h;
 end
+
+%% Problem 6 (functions)
+
+function [C] = matTimesMat_classical(A, B)
+s = size(A);
+n = s(1);
+C = zeros(n);
+for i=1:n
+    for j=1:n
+        for k=1:n
+            C(i,j) = C(i,j) + A(i,k) * B(k,j);
+        end
+    end
+end
+end
+
+function [C] = matTimesMat_column(A, B)
+s = size(A);
+n = s(1);
+C = zeros(n);
+for j=1:n
+    for k=1:n
+        C(:,j) = C(:,j) + B(k,j) * A(:,k);
+    end
+end
+end
+
+function [C] = matTimesMat_outerProd(A, B)
+s = size(A);
+n = s(1);
+C = zeros(n);
+for j=1:n
+    C = C + A(:,j) * B(j,:);
+end
+end