Asked by Lalit Patil
on 26 Nov 2012

I have a Three parameters Xi,Yi,Zi.. and I am finding a SVD of them..

A=[Xi,Yi,Zi,ones(length(Xi),1)];

[U,S,V]=svd(A);

ss=diag(S);

i=find(ss==min(ss));

coeff=V(:,min(i));

coeff=coeff/norm(coeff(1:3),2);

and i am getting four parameters for plane.. the code is ok.. but,

is there any method to do SVD without using SVD function..?

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Answer by Walter Roberson
on 26 Nov 2012

Source code is at http://www.netlib.org/lapack/double/dgesvd.f

Lalit Patil
on 27 Nov 2012

But , I can't understand what the sequence is of mathematical equations.?

I want That equations or code which can be applied insted of SVD functions..

Walter Roberson
on 27 Nov 2012

**is** the code that is used by MATLAB (though it is not impossible that Mathworks has tweaked the code.) Everything that is documented about **exactly** how MATLAB's SVD function operates is in that source code (when you include the related files for the routines it calls.)

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## 6 Comments

## Walter Roberson (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113410

can be replaced with

and you will not need to take min(i) on the next line, just i.

## Walter Roberson (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113411

Is there a particular reason for wanting to do SVD without using the SVD function? Knowing your reason might help people select the best alternative for you.

## Lalit Patil (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113413

SVD is almost used at many application, and one of its feature is it gives a best fit..

So, i want to know actually what real procedure happens inside SVD function so that it gives best fit..

I want to know this for my best plane fitting a*X + b*Y + c*Z + d = 0 from so many plane equations..

## Walter Roberson (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113415

http://www.mathworks.com/company/newsletters/articles/professor-svd.html

## Lalit Patil (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113417

This is not that thing which i want..

I want to know that what procedure happened inside SVD matlab function so that U,S,V get generated..?

Actually i want to write code for that..

## Walter Roberson (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/54780#comment_113419

The blog has a bunch of links.