Here is a simpler question. Is there a tacit version of ff below?
u =: 2 3 0
v =: i. 3 3
ff =: 4 : 'x ({. x)} y'
u ff v
0 1 2
3 4 5
2 3 0
--Kip Murray
Sent from my iPad
> On Jan 12, 2014, at 10:41 PM, Raul Miller <[email protected]> wrote:
>
> Sometimes it helps to inspect intermediate results. With recursion,
> though, it can be a bit tricky for a casual observer to see the
> intermediate results. With that in mind, here's what I am seeing for
> your example:
>
> a1=: (calcU calcL) saveAA
> a2=: (calcU calcL) a1
> a3=: (calcU calcL) a2
>
> A4=: ((({.@[ ,: ]) ,&.:(|."1) a3"_) calcL) a2
> A5=: ((({.@[ ,: ]) ,&.:(|."1) A4"_) calcL) a1
> A6=: ((({.@[ ,: ]) ,&.:(|."1) A5"_) calcL) saveAA
>
> a1, a2 and a3 are progressively smaller square matrices (2x2, 1x1, 0x0)
>
> A4, A5 and A6 are progressively larger matrices which are twice as
> tall as wide. If you could compute them in reverse order it might have
> made sense to make it twice as wide as tall (with intermediate lu side
> by side instead of interleave stacked)?
>
> A6 is the same as lumain saveAA
>
> I should go back and re-read km's implementation. But I will note that
> you can cut code size slightly using some cross hooks:
>
> lumain =: (((,:~ {.)~ ,&.:(|."1) $:@calcU) calcL)^:(*@#)
> lu =: [: (,:~ |:)/ 1 0 2 |: _2 ]\ lumain
>
> Anyways, I think your O(n^3) space is largely because all intermediate
> values from what I have characterized as a (calcU calcL) hook are
> "pre"-computed and placed on the stack before proceeding with further
> computations.
>
> Thanks,
>
> --
> Raul
>
>> On Sun, Jan 12, 2014 at 10:10 PM, Henry Rich <[email protected]> wrote:
>> calcL =: (% {.)@:({."1)
>> calcU =: (}.@[ - {.@[ *"1 0 ])&:(}."1)
>> lumain =: ((({.@[ ,: ]) ,&.:(|."1) $:@calcU) calcL)^:(*@#)
>> lu =: [: (|:@] ,: [)/ 1 0 2 |: _2 ]\ lumain
>> NB. Half this code is handling joining ragged lists.
>> NB. Is there a better way?
>>
>> saveAA =: 3 3 $ 2 1 4 _4 _1 _11 2 4 _2
>> lu saveAA
>>
>> 1 0 0
>> _2 1 0
>> 1 3 1
>>
>> 2 1 4
>> 0 1 _3
>> 0 0 3
>>
>> I suspect that a vectorized explicit version is a better way to go. This
>> version has memory requirements of O(n^3).
>>
>> Henry Rich
>>
>>
>>> On 1/12/2014 9:00 PM, km wrote:
>>>
>>> Verb LU below produces the matrices L and U of the LU decomposition of a
>>> square matrix A. L is lower triangular, U is upper triangular, and A is L
>>> +/ . * U .
>>>
>>> Should one attempt a tacit version?
>>>
>>> eye =: =@i.@] NB. eye 3 is a 3 by 3 identity matrix
>>>
>>> rop =: 3 : 0 NB. row op: subtract c times row i0 from row i1
>>> :
>>> 'i1 c i0' =. x
>>> ( (i1 { y) - c * i0 { y ) i1 } y
>>> )
>>>
>>> LU =: 3 : 0 NB. square matrices L and U for y -: L +/ . * U
>>> m =. # y
>>> L =. eye(m)
>>> U =. y
>>> for_j. i. <: m do.
>>> p =. (< j , j) { U
>>> for_i. j + >: i. <: m - j do.
>>> c =. p %~ (< i , j) { U
>>> L =. c (< i , j) } L
>>> U =. (i, c, j) rop U
>>> end.
>>> end.
>>> L ,: U
>>> )
>>>
>>> saveAA
>>> 2 1 4
>>> _4 _1 _11
>>> 2 4 _2
>>>
>>> LU saveAA
>>> 1 0 0
>>> _2 1 0
>>> 1 3 1
>>>
>>> 2 1 4
>>> 0 1 _3
>>> 0 0 3
>>>
>>> saveAA -: +/ . */ LU saveAA
>>> 1
>>>
>>> --Kip Murray
>>>
>>> Sent from my iPad
>>> ----------------------------------------------------------------------
>>> For information about J forums see http://www.jsoftware.com/forums.htm
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
