# Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 2.202823e-18.

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Rui Mauaie 2018년 11월 13일
댓글: Tugcan 2024년 1월 6일
hi guys I need a help I'm using LDA but when I run I got the message aforementioned
S1=cov(d1');
S2=cov(d2');
S3=cov(d3');
%% within-class scatter matrix
Sw=S1+S2+S3;
%% between -class scatter matrix
SB1=n1.* (mu1-mu)*(mu1-mu)';
SB2=n2.* (mu2-mu)*(mu2-mu)';
SB3=n3.* (mu3-mu)*(mu3-mu)';
SB=SB1+SB2+SB3;
%% Computing the LDA projection
W=inv(Sw)*SB;
%% getting the projection vectors
[V,D]=eig(W);

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### 채택된 답변

Jan 2018년 11월 13일
The error message is clear. I guess it occurs for this line:
W=inv(Sw)*SB;
This means, that Sw is ill-conditioned, such that there is no inverse of it. This is equivalent to dividing by zero. There is no "help" for this case, but the inputs do not allow this operation.
By the way, use
W=Sw \ SB
instead of the explicit inversion for numerical reasons. See doc inv .
##### 댓글 수: 3이전 댓글 1개 표시이전 댓글 1개 숨기기
Torsten 2018년 11월 13일
Sw\SB, not Sw/SB !
Bruno Luong 2018년 11월 13일
편집: Bruno Luong 2018년 11월 13일
Sw\SB
is based on QR with column permutation, so if you system is ill-conditions, it let some of the components of the unknown W to be 0.
pinv(Sw)*SB
is based on SVD, so it forces the projection of the unknown W to the span of the degenerated singular vectors to be 0.
Generally SVD solution is "better", in the sense that is the smallest vector (in l2 norm) that meets the solution (or minimizes the residual l2 norm), therefore more stable with respect to noise.

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### 추가 답변 (3개)

Tony Castillo 2020년 1월 16일
Hello Guys,
Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 2.051867e-16.
Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 2.051867e-16.
May you help me to solve it ?
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Marcel Johannesmann 2020년 7월 25일
편집: Marcel Johannesmann 2020년 7월 26일
I have encountered a similar warning. I could narrow it down to the Load flow settings of the power gui block. The warning most likely occurs because your Base Power is too high so that your rated values (in pu) in the admittance matrix are getting too small. Adjusting the base power fixed this issue for me. Hope this helps.
Mojtaba Raheli 2020년 9월 27일
편집: Mojtaba Raheli 2020년 9월 27일
How did you do it? I cannot adjust base power. please write the direction of base power setting.

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이 답변에 John D'Errico 님이 플래그를 지정함
clc;
clear;
close all;
A = [2 1 -5; 0 1 -2; 0 0 2];
[P, D] = eig(A);
disp('P Matrix');
P Matrix
disp(P);
1.0000 -0.7071 1.0000 0 0.7071 -0.0000 0 0 0.0000
disp('Diagonal form of A is');
Diagonal form of A is
disp(P\D*P);
Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 6.344132e-17.
2.0000 -0.7071 0.0000 0 1.0000 0.0000 0 0 2.0000
##### 댓글 수: 9이전 댓글 7개 표시이전 댓글 7개 숨기기
John D'Errico 2021년 10월 22일
편집: John D'Errico 2021년 10월 22일
@Shaunak Bagade - what did you not get? I will not answer your question, not UNTIL you bother to post this as a question. Nor should anyone else. So while your question is of technical interest, posting it as an answer to a different question is a problem, because that means nobody else will ever be able to find your question, and nobody else will be able to learn from the answer. Effectively, if you are interested in learning the answer to this problem, then you should be interested enough to learn to use the site properly.
Note that as quasi-moderators, we should have the capability to move this into a question by the OP. But that is beyond our abilities.
John D'Errico 2021년 10월 22일
@Shaunak Bagade - Since you seem not to want to follow my guidance, see my question, AND answer, here:
From now on, please learn to post a question as a question, rather than hijacking a separate only vaguely related question.

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Tugcan 2024년 1월 5일
Hello guys i had a same error with different matlabs code. I tried this \ method but still i have this error. I get this error at values 80 120 and 320 for N. Best Regards.
Enter T:
1
Enter N:
80
Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 5.765040e-19. > In question4s (line 18)
error =
1.8689e+13
function mixedboundary()
T=input("Enter T: ");
N=input("Enter N: ");
h=T/N;
A=zeros(N+1,N+1);
F=zeros(N+1,1);
A(1,1)=1;
A(N+1,1:3)=[-3, 4, -1];
F(1,1)=1;
F(N+1,1)=6*h;
for i=2:N
t(i)=(i-1)*h;
A(i,i-1)=1/(h^2)-5/(h);
A(i,i)=-2/(h^2)-3/(2*h);
A(i,i+1)=1/(h^2)-5/(h);
F(i,1)=14*exp(2*t(i))-3*exp(4*t(i));
end
Y=inv(A)*F;
exact=zeros(N+1,1);
for i=1:N+1
t(i)=(i-1)*h;
exact(i,1)=exp(2*t(i));
end
error=max(abs(exact-Y))
end
##### 댓글 수: 4이전 댓글 2개 표시이전 댓글 2개 숨기기
Torsten 2024년 1월 5일
편집: Torsten 2024년 1월 5일
The code has nothing to do with your assignment.
The method used in the code is suited for boundary value problems - thus problems where conditions on the solution are imposed at both ends of the interval of integration (in your case: t = 0 and t = T). In the assignment, both conditions are imposed at t = 0.
Further, you are told to first reduce the 2nd order differential equation to a system of two first order differential equations and then solve the system by a Runge-Kutta-method. Both does not happen in the code.
Tugcan 2024년 1월 6일
I see. I have reduced formst but i dont know how to evolve it to Runge-Kutta-Method but thank you for attention

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