| Re: 3d matrices and LUSOL [message #28986 is a reply to message #28982] |
Fri, 25 January 2002 08:13   |
Manish
Messages: 20
Registered: April 2001
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Junior Member |
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Cheers guys, that should sort it - it was exactly what I needed!
I'll give it a go with INVERT first with the looped arrays, maybe try and
refine it to LUSOL later on if I get I working!
Both of you, thanks for your help again
Manish.
"trouble" <the_cacc@hotmail.com> wrote in message
news:5f9f0a23.0201241522.7f538c34@posting.google.com...
> "M" <mrmanish@bigfoot.com> wrote in message
news:<a2pj2t$jv8$1@yarrow.open.ac.uk>...
>> Hi all,
>>
>> I am in desperate need of help!!
>>
>> I have a set of linear equations represented as matrix arrays which need
to
>> be solved using the LU decomposition technique. The two arrays consist
of a
>> 14 x 14 array, and a 14 x 1 array, but each element in the matrices
itself
>> is an array of 221 elements ( ie the matrices are 3dimensional...?)
>>
>> So i need to solve the system using LUDC and LUSOL, but i have to do it
221
>> times (ie a solution for each 'layer' of the matrices)
>>
>> The first question is, is there a way to declare the two input arrays as
>> 3-d? I tried defining the matrix using matrix=[[a,b,..],[...,...,...]
etc]
>> where a,b,... = arrays, but this isn't recognised as a 14 x14 square
matrix
>> which is 221 elements 'deep'. Instead, it expands each array across the
>> row, making it a 3094 x 14 matrix. (it needs to be square to run LUDC)
>>
>> Is there a way i can force IDL to see it as a 'layered' 3-d matrix?
>>
>> What i need to achieve is a 3 dimensional 14 x 1 solution array, again
221
>> elements 'deep'. To get this, could i simply run LUDC and LUSOL as
normal
>> provided the inputs are 3d matrices, or do i need to somehow loop the
>> procedures so it produces solutions one 'layer' at a time and builds
them
>> into the 3 d solution matrix ?
>>
>> I don't know if anyone has any idea of what i'm talking about, but i
only
>> just understand it myself!!
>> Apologies if it makes no sense whatsoever, suffice to say i'm a little
>> confused right now!
>>
>>
>> Any insight into the above would be great,
>>
>> thanks,
>>
>> Manish.
>
> Hi,
>
> From what you say, it sounds like you want to be solving the 14x14
> problem 221 times, ie.
>
> For the first 14x14 matrix (A1) and 14x1 vector (b1), solve for x1:
> x1 = INVERT(A1) ## b1
>
> Then for the second case: x2 = INVERT(A2) ## b2
>
> and so on 221 times. You'll then have 221 14x1 vectors x1,x2,... which
> together give a 2D matrix (221x14).
>
> Is this what you were expecting as your answer ? If so, then yay! If
> not, I haven't understood the problem :(
>
> Of course, you can define the individual matrices in larger matrices,
> ie. A = FLTARR(14,14,221), b = FLTARR(14,221) and x = FLTARR(14,221)
> then loop as follows:
>
> FOR i = 0, 220 DO x[*,i] = INVERT(A[*,*,i]) ## b[*,i]
>
>
> NOTE: using LUDC and LUSOL directly is slightly faster than using
> INVERT, but you may prefer INVERT initially since it makes the code
> simpler.
>
> Ciao.
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