MATLAB Central Newsreader - Divide, operate and reassemble matrix

Divide, operate and reassemble matrix

Diego Lass — Thu, 18 Jun 2009 21:23:01 -0400

Hi
I have a problem with a large matrix, what I want to do is to divide the matrix into 4 submatrices, do some operation then reassemble the submatrix together. A toy example

A = [1 2 3 ; 3 4 5 ; 2 3 4; 5 1 2 ]
A =

     1 2 3
     3 4 5
     2 3 4
     5 1 2
I want to divide A into ANY 4 approximately equal sized partitions, for example
1 2
3 4

3
5

2 3
5 1

4
2

then do some operation, say add 2 to each element. Then reassemble them together, to get

     3 4 5
     5 6 7
     4 5 6
     7 3 4
What is the most efficient way of doing this?
Thanks
Diego

Re: Divide, operate and reassemble matrix

Nathan — Thu, 18 Jun 2009 21:30:10 -0400

On Jun 18, 2:23 pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> Hi
> I have a problem with a large matrix, what I want to do is to divide the matrix into 4 submatrices, do some operation then reassemble the submatrix together. A toy example
>
> A = [1 2 3 ; 3 4 5 ; 2 3 4; 5 1 2 ]
> A =
>
> 1 2 3
> 3 4 5
> 2 3 4
> 5 1 2
> I want to divide A into ANY 4 approximately equal sized partitions, for example
> 1 2
> 3 4
>
> 3
> 5
>
> 2 3
> 5 1
>
> 4
> 2
>
> then do some operation, say add 2 to each element. Then reassemble them together, to get
>
> 3 4 5
> 5 6 7
> 4 5 6
> 7 3 4
> What is the most efficient way of doing this?
> Thanks
> Diego

You just posted this not an hour ago with a different title... Why?

Why disassemble and do operations when you can just do that operation
to each element in one instruction?

Re: Divide, operate and reassemble matrix

Diego Lass — Thu, 18 Jun 2009 21:41:01 -0400

Oh, because when I run whatever I wrote, I got the following error

??? Error using ==> minus
Maximum variable size allowed by the program is exceeded.

Error in ==> [some program] at 18
[equation involves matrix .*, ./ and (1 - some matrix .^)]

However, when I tested on a smaller matrix, the code works
So I was thinking maybe if I divide the matrix into submatrices, do the thing and reassemble them, the code might work.

Thanks
Diego

Nathan <ngreco32@gmail.com> wrote in message <728fb21e-1182-4780-b27d-44a4d369d85f@o21g2000prn.googlegroups.com>...
> On Jun 18, 2:23?pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> > Hi
> > I have a problem with a large matrix, what I want to do is to divide the matrix into 4 submatrices, do some operation then reassemble the submatrix together. A toy example
> >
> > A = [1 2 3 ; 3 4 5 ; 2 3 4; 5 1 2 ]
> > A =
> >
> > ? ? ?1 2 3
> > ? ? ?3 4 5
> > ? ? ?2 3 4
> > ? ? ?5 1 2
> > ?I want to divide A into ANY 4 approximately equal sized partitions, for example
> > 1 2
> > 3 4
> >
> > 3
> > 5
> >
> > 2 3
> > 5 1
> >
> > 4
> > 2
> >
> > then do some operation, say add 2 to each element. Then reassemble them together, to get
> >
> > ? ? ?3 4 5
> > ? ? ?5 6 7
> > ? ? ?4 5 6
> > ? ? ?7 3 4
> > What is the most efficient way of doing this?
> > Thanks
> > Diego
>
> You just posted this not an hour ago with a different title... Why?
>
> Why disassemble and do operations when you can just do that operation
> to each element in one instruction?

Re: Divide, operate and reassemble matrix

Nathan — Thu, 18 Jun 2009 21:54:43 -0400

On Jun 18, 2:41 pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> Oh, because when I run whatever I wrote, I got the following error
>
> ??? Error using ==> minus
> Maximum variable size allowed by the program is exceeded.
>
> Error in ==> [some program] at 18
> [equation involves matrix .*, ./ and (1 - some matrix .^)]
>
> However, when I tested on a smaller matrix, the code works
> So I was thinking maybe if I divide the matrix into submatrices, do the thing and reassemble them, the code might work.
>
> Thanks
> Diego
>
> Nathan <ngrec...@gmail.com> wrote in message <728fb21e-1182-4780-b27d-44a4d369d...@o21g2000prn.googlegroups.com>...
> > On Jun 18, 2:23?pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> > > Hi
> > > I have a problem with a large matrix, what I want to do is to divide the matrix into 4 submatrices, do some operation then reassemble the submatrix together. A toy example
>
> > > A = [1 2 3 ; 3 4 5 ; 2 3 4; 5 1 2 ]
> > > A =
>
> > > ? ? ?1 2 3
> > > ? ? ?3 4 5
> > > ? ? ?2 3 4
> > > ? ? ?5 1 2
> > > ?I want to divide A into ANY 4 approximately equal sized partitions, for example
> > > 1 2
> > > 3 4
>
> > > 3
> > > 5
>
> > > 2 3
> > > 5 1
>
> > > 4
> > > 2
>
> > > then do some operation, say add 2 to each element. Then reassemble them together, to get
>
> > > ? ? ?3 4 5
> > > ? ? ?5 6 7
> > > ? ? ?4 5 6
> > > ? ? ?7 3 4
> > > What is the most efficient way of doing this?
> > > Thanks
> > > Diego
>
> > You just posted this not an hour ago with a different title... Why?
>
> > Why disassemble and do operations when you can just do that operation
> > to each element in one instruction?

Are you using bsxfun?
If not, check that out. It might be what you're looking for.

Re: Divide, operate and reassemble matrix

Diego Lass — Thu, 18 Jun 2009 22:03:01 -0400

Well, I want to calculate the t-stat of a correlation matrix, i.e.

Tstat = correlation .* sqrt((nv-2) ./ (1 - correlation.^2));

nv is the degree of freedom. I am not sure how to do that with bsxfun.

Diego

Nathan <ngreco32@gmail.com> wrote in message <092599c9-0913-410c-8f88-cc3911772334@x31g2000prc.googlegroups.com>...
> On Jun 18, 2:41?pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> > Oh, because when I run whatever I wrote, I got the following error
> >
> > ??? Error using ==> minus
> > Maximum variable size allowed by the program is exceeded.
> >
> > Error in ==> [some program] at 18
> > ? ?[equation involves matrix .*, ./ and (1 - some matrix .^)]
> >
> > However, when I tested on a smaller matrix, the code works
> > So I was thinking maybe if I divide the matrix into submatrices, do the thing and reassemble them, the code might work.
> >
> > Thanks
> > Diego ?
> >
> > Nathan <ngrec...@gmail.com> wrote in message <728fb21e-1182-4780-b27d-44a4d369d...@o21g2000prn.googlegroups.com>...
> > > On Jun 18, 2:23?pm, "Diego Lass" <dlISC...@gmail.com> wrote:
> > > > Hi
> > > > I have a problem with a large matrix, what I want to do is to divide the matrix into 4 submatrices, do some operation then reassemble the submatrix together. A toy example
> >
> > > > A = [1 2 3 ; 3 4 5 ; 2 3 4; 5 1 2 ]
> > > > A =
> >
> > > > ? ? ?1 2 3
> > > > ? ? ?3 4 5
> > > > ? ? ?2 3 4
> > > > ? ? ?5 1 2
> > > > ?I want to divide A into ANY 4 approximately equal sized partitions, for example
> > > > 1 2
> > > > 3 4
> >
> > > > 3
> > > > 5
> >
> > > > 2 3
> > > > 5 1
> >
> > > > 4
> > > > 2
> >
> > > > then do some operation, say add 2 to each element. Then reassemble them together, to get
> >
> > > > ? ? ?3 4 5
> > > > ? ? ?5 6 7
> > > > ? ? ?4 5 6
> > > > ? ? ?7 3 4
> > > > What is the most efficient way of doing this?
> > > > Thanks
> > > > Diego
> >
> > > You just posted this not an hour ago with a different title... Why?
> >
> > > Why disassemble and do operations when you can just do that operation
> > > to each element in one instruction?
>
> Are you using bsxfun?
> If not, check that out. It might be what you're looking for.