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diff --git a/191/CH4/EX4.13/Example4_13.sce b/191/CH4/EX4.13/Example4_13.sce
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+//Orthogonal decomposition - QR method
+//reduce A to tridiagonal form
+clc;
+clear;
+close();
+format('v',7);
+A1 = [1 4 2;-1 2 0;1 3 -1];
+disp(A1, 'A = ');
+// zero is created in lower triangle
+//by taking the rotation matrix X1=[c s 0;-s c 0;0 0 1]; where c=cos and s=sin
+//O is theta
+
+Q = eye(3,3);
+for i=2:3
+    for j=1:i-1
+        p=i;q=j;
+        O = -atan(A1(p,q)/(A1(q,q)));
+        c = cos(O);
+        s = sin(O);
+        X = eye(3,3);
+        X(p,p)=c;
+        X(q,q)=c;
+        X(p,q)=-s;
+        X(q,p)=s;
+        A1 = X'*A1;  
+        Q = Q*X;
+        disp(A1,X,'The X and A matrix : ');
+    end
+end
+R = A1;
+disp(R,Q,'Hence the original matrix can be decomposed as : ')
+\ No newline at end of file