# Index exceeds the number of array elements (1)

조회 수: 6(최근 30일)
Jonas Freiheit 9 Sep 2020
댓글: Jonas Freiheit 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

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### 채택된 답변

Kojiro Saito 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)

#### 댓글 수: 9

표시 이전 댓글 수: 6
Jonas Freiheit 10 Sep 2020
Yeah, including this code with only changing from the bold text code.
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 %Here
[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 %End
Thanks, Kojiro
Kojiro Saito 10 Sep 2020
It's not possible only changing the bold text code because the funtion pivoting requires three inputs, so you need to modify input variables so that it allows two inputs.
Jonas Freiheit 10 Sep 2020
Alright that makes sense,
Thanks for the help Kojiro!

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R2020a

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