+/ M e."_ 0 V
does the job
Am 26.12.20 um 00:55 schrieb Thomas Bulka:
> Hello forum,
>
> currently I try to make use of the Fold family of primitives to achieve
> a rather simple (I think) task. However, I have not been able to reach
> the desired goal. This is, what I want to do:
>
> Suppose, I have some matrix M and some vector V:
>
> M =: 3 4 $ 12?12
> V =: 1 2 3
>
> I now want to apply each element of V to the whole of M (an operation
> which is supposed to give a result with the same size of M). I want to
> give a short exemplary demonstration of the data flow I imagine:
>
> M => Start
> 7 4 11 3
> 0 1 6 10
> 9 2 5 8
>
> M1 => (M e. 0 { V)
> 0 0 0 0
> 0 1 0 0
> 0 0 0 0
>
> M2 => (M e. 1 { V)
> 0 0 0 0
> 0 0 0 0
> 0 1 0 0
>
> M3 => (M e. 2 { V)
> 0 0 0 1
> 0 0 0 0
> 0 0 0 0
>
> Result => M1 + M2 + M3
> 0 0 0 1
> 0 1 0 0
> 0 1 0 0
>
> To me it seems, that this would be a task for the Fold family of
> primitives, but I don’t seem to be able to get my head around this. I’d
> very much appreciate any hints on how to implement this with Fold - and
> of course I’d like to know, whether my intuition, that the Fold family
> would be the right tool for the job, is right or if there are better
> options.
>
> Happy holidays to everyone and kind regards,
>
> Thomas
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