Gauss Seidel Method problem

I have to write two codes one for Jacobi and one for Gauss Schiedel

For the Gauss Schiedel one I coded

clc

clear

a=[1.2528,-1.4031,-2.45;0,3.3659,-0.2;1.6094,-3.8357,-5];

b=[-0.56,1.18,-6.37]';

x=[0,0,0]';

err=9000;

tol=0.01;

n=length(x);

while err>tol

x_1=x;

for i=1:n

sum=0;

for j=1:i-1

sum_1=sum+a(i,j)*x(j);

end

for j=i:n

sum_2=sum+a(i,j)*x_1(j);

end

x(i)=1/a(i,i)*(b(i)-(sum_1)-sum_2);

end

end

and in the error it says Unrecognized function or variable 'sum_1' for x(i)=1/a(i,i)*(b(i)-(sum_1)-sum_2); despite the fact that it is clearly stated before that there is a sum_1. Why is matlab not recognising the variable?

Answer 1

[David Hill]

sum_1 is not assigned before it is needed (for loop does not execute immediately). Recommend assigning sum_1 = 0 outside the while loop.