# Lab 7 Solutions

## Topics in this lab

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## Exercise 2

A = [1 -1 3; 3 5 -1; 0 5 -3]; b = [5;1;-22]; x = A\b

x = 10.3846 -6.8462 -4.0769

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## Exercise 3

A = [1 -4 4; -1 1 -2; 1 1 -1]; b = [0; 1; -2]; x = A\b

x = -1.6000 -0.2000 0.2000

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## Exercise 4

x = [1,2,3]; y = [3,5,-1]; A = [x(:).^2 x(:) ones(3,1)]; b = y(:); p = A\b

p = -4.0000 14.0000 -7.0000

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## Exercise 5

z = ones(5,1); A = spdiags([z -2*z z],-1:1,5,5); b = ones(5,1); A full(A) x = A\b

A = (1,1) -2 (2,1) 1 (1,2) 1 (2,2) -2 (3,2) 1 (2,3) 1 (3,3) -2 (4,3) 1 (3,4) 1 (4,4) -2 (5,4) 1 (4,5) 1 (5,5) -2 ans = -2 1 0 0 0 1 -2 1 0 0 0 1 -2 1 0 0 0 1 -2 1 0 0 0 1 -2 x = -2.5000 -4.0000 -4.5000 -4.0000 -2.5000

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## Get the code

Do you want to try the above code fragments on your own? Download the Matlab script that produces this page here. (lab_7_solns.m)

Published with MATLAB® 8.5