t -: (2{.s) $ x /:&; </.i.s
1
On Thu, Jan 31, 2013 at 10:47 AM, Roger Hui <[email protected]>wrote:
> t=: 5 7 2 ?@$ 1e6
> s=: $t
> x=: </.t
>
> t -: (2{.s) $ (;x)/:;</.i.s
> 1
>
>
>
> On Thu, Jan 31, 2013 at 10:28 AM, Raul Miller <[email protected]>wrote:
>
>> Let's start with an arbitrary array:
>>
>> A=: i. 2 3
>>
>> We can box oblique lines from this array:
>>
>> </. A
>> +-+---+---+-+
>> |0|1 3|2 4|5|
>> +-+---+---+-+
>>
>> However, the interpreter does not currently provide us with an inverse
>> for this operation:
>>
>> </.inv </. A
>> |domain error
>>
>> One problem is that you cannot uniquely determine the first two
>> elements of the shape of the original array by inspecting </.'s
>> result:
>>
>> (</. 5 7$0) -: </.7 5$0
>> 1
>>
>> If its shape is provided, how might we reconstruct the original array?
>>
>> [For the sake of simple code, it's ok to focus on numeric, rank 2 arrays.]
>>
>> --
>> Raul
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>>
>
>
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