Page 231 - MATLAB an introduction with applications

216 ——— MATLAB: An Introduction with Applications

Run_pr_E4.2.m

A = [2 1 1 –1;1 5 –5 6; –7 3 –7 –5; 1 –5 2 7];
b = [10;25;5;11];
[x, det] = gauss(A,b)
x = A\b
gauss.m
function [x,det] = gauss(A,b)
% Solves A*x = b
if size(b,2) > 1; b = b’; end
n = length(b);
for k = 1:n–1
for i= k+1:n
if A(i,k) ~ = 0
lambda = A(i,k)/A(k,k);
A(i,k+1:n) = A(i,k+1:n) – lambda*A(k,k+1:n);
b(i)= b(i) – lambda*b(k);
end
end
end
if nargout == 2; det = prod(diag(A)); end
for k = n:–1:1
b(k) = (b(k) – A(k,k+1:n)*b(k+1:n))/A(k,k);
end
x = b;

MATLAB Solution [Using built-in function]:

>> A = [2 1 1 –1;1 5 –5 6;–7 3 –7 –5;1 –5 2 7];
>> B = [10;25;5;11];
>> x = A\B
x =
25.3587
–19.6143
–28.9058
–7.8027
>> x = inv(A) * B
x =
25.3587