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| LanceMD@gmail.com 2007-02-27, 6:57 pm |
| I have a Matrix M. Let's say it's shape is 8 8
I want all elements in a particular row combined with all elements
from a particular column. Lets say V{<--}2 5. That is the third row
and sixth column (quadIO is 0)
So my code looks like
M[V[0] ; ],M[ ; V[1]]
Is there a way of doing this referring to M only once?
For example:
,M[code]
I'm using APL+Win 2.0
Thanks,
Lance
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| Ted Edwards 2007-02-27, 6:57 pm |
| LanceMD@gmail.com wrote:
> I have a Matrix M. Let's say it's shape is 8 8
> I want all elements in a particular row combined with all elements
> from a particular column. Lets say V{<--}2 5. That is the third row
> and sixth column (quadIO is 0)
>
> So my code looks like
>
> M[V[0] ; ],M[ ; V[1]]
>
> Is there a way of doing this referring to M only once?
Why do you care? I'm using APL2 on a ThinkPad T23
and
'TIMER' 'ToASCII' need 'tutil' 'charset'
{quad}IO{is}0
M{is}r{rho}{iota}{times}/r{is}10 20
1000 TIMER'{rho}M[V[0];],M[;V[1]]'
0.000036
M{is}r{rho}{iota}{times}/r{is}1000 2000
1000 TIMER'{rho}M[V[0];],M[;V[1]]'
0.000475
M{is}0.1{times}?(r{is}10 20){rho}1000
1000 TIMER'{rho}M[V[0];],M[;V[1]]'
0.000037
M{is}0.1{times}?(r{is}1000 2000){rho}1000
1000 TIMER'{rho}M[V[0];],M[;V[1]]'
0.000566
That last is half a millisecond for a random two million element
floating point array. (TIMER did it 1000 times and divided the result by
1000.)
Ted
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| Ibeam2000 2007-02-27, 6:57 pm |
| It depends on what you really mean by "referring to". You need to get
the shape of M in order to construct the indices to make (,M)[code]
work.
Something like
(,M)[ (rho M) encode (V[0],[-0.5] iota 1 drop rho M),(iota 1 take rho
M),[-0.5] V[1] ]
[]io must be zero.
This code fragment should work on nearly all APL versions known to
man.
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| graham 2007-02-27, 6:57 pm |
|
<LanceMD@gmail.com> wrote in message
news:1172594281.164464.102030@t69g2000cwt.googlegroups.com...
>I have a Matrix M. Let's say it's shape is 8 8
> I want all elements in a particular row combined with all elements
> from a particular column. Lets say V{<--}2 5. That is the third row
> and sixth column (quadIO is 0)
> Is there a way of doing this referring to M only once?
> For example:
>
> ,M[code]
> Lance
I agree with the other responses you have had about why would you want to do
it and what you mean by referring to M only once. If you already know the
shape of M and it is fixed then yes the code in index origin 1 is simply:
(,M)[(({iota}8)+8×R-1),C+8×0,{iota}7]
where R is the row you want and C the column.
Graham.
| |
| Seth Breidbart 2007-03-28, 7:58 am |
| In article <Fo_Eh.648$Xi2.491@edtnps89>,
Ted Edwards <Ted_Espamless@telus.net> wrote:
>LanceMD@gmail.com wrote:
>
>Why do you care?
Maybe M is computed and he doesn't want to store it.
Seth
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| yashchi 2007-04-29, 1:41 pm |
| quote:
Originally posted by graham
<LanceMD@gmail.com> wrote in message
news:1172594281.164464.102030@t69g2000cwt.googlegroups.com...
>I have a Matrix M. Let's say it's shape is 8 8
> I want all elements in a particular row combined with all elements
> from a particular column. Lets say V{<--}2 5. That is the third row
> and sixth column (quadIO is 0)
> Is there a way of doing this referring to M only once?
> For example:
>
> ,M[code]
> Lance
I agree with the other responses you have had about why would you want to do
it and what you mean by referring to M only once. If you already know the
shape of M and it is fixed then yes the code in index origin 1 is simply:
(,M)[(({iota}8)+8×R-1),C+8×0,{iota}7]
where R is the row you want and C the column.
Graham.
There is another way to achieve this goal (scatter indexing) for APL2:
(R ({iota}8))(({iota}8) C){Index} {Each} {Enclose} M
see Brown, Pakin and Polivka "APL2 at a glance", p.396. |
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