# Index exceeds the number of array elements (1)

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Jonas Freiheit on 9 Sep 2020
Commented: Jonas Freiheit on 10 Sep 2020
%When I try to perform a row interchange for 'b' vector It tells me it exceeds the no of array elements. This is an attempt to perform partial pivoting for matrix A and vector b separately.
Thanks
A = [1 2 3;4 2 -1; 3 2 3];
b = [1; 3; 2];
k = 1;
A = pivoting(A,k)
function [A, b, flag] = pivoting(A, b, k)
n = size(A,1);
flag = 0;
for k=1:n-1
[big, i]=max(abs(A(k:n,k)))
ipr=i+k-1
if ipr~=k
A([k,ipr],:)=A([ipr,k],:)
b([k,ipr])=b([ipr,k])
end
end
end

Kojiro Saito on 9 Sep 2020
It's because you're trying to manipulate b in line,
b([k,ipr])=b([ipr,k])
but, you're inputting as follows.
k = 1;
A = pivoting(A,k)
so, in function pivoting, b (second input variable) is scalar (1).
You just need to input three variables.
% A = pivoting(A,k)
A = pivoting(A,b,k)
Jonas Freiheit on 10 Sep 2020
Alright that makes sense,
Thanks for the help Kojiro!

R2020a

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