Decode problem

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Decode problem

Postby hbarkhof on Wed Aug 01, 2018 9:33 am

In the book : "Mastering Dyalog APL" , page 461 exercise K-1

The question(s):

What is the result of :
a) 0 ⊥ 12 34 60 77 19
b) 1 ⊥ 12 34 60 77 19

Results in 19 and 202 respectively. No problem here
a) +/(12×0) (34×0) (60×0) (77×0) 19
b) +/ 12 34 60 77 19

But what happens with:

2 ⊥ 12 34 60 77 19 (results in 877 , but how?)

I was thinking that I understood ENCODE and DECODE but apparently.... :-(
hbarkhof
 
Posts: 29
Joined: Mon Apr 09, 2018 8:37 am

Re: Decode problem

Postby Veli-Matti on Wed Aug 01, 2018 9:57 am

Perhaps this will explain it better:
      +/ 12 34 60 77 19 × 2*4 3 2 1 0
877


-Veli-Matti
Veli-Matti
 
Posts: 41
Joined: Sat Nov 28, 2009 3:12 pm

Re: Decode problem

Postby hbarkhof on Wed Aug 01, 2018 12:58 pm

Ah , thus with a 3 the result would be :

+/ 12 34 60 77 19 × 3*4 3 2 1 0

Resulting in 2680

Thanks for explaning , colour me red ! :-)
hbarkhof
 
Posts: 29
Joined: Mon Apr 09, 2018 8:37 am

Re: Decode problem

Postby Veli-Matti on Thu Aug 02, 2018 10:07 am

This might give some kind of insight as well:
      ⎕IO←1
0⊥12 34 60 77 19
19
0{⍺⊥⍵}12 34 60 77 19
19
1{+/⍵×⍺*⌽¯1+⍳≢⍵}12 34 60 77 19
202
2{+/⍵×⍺*(≢⍵)-⍳≢⍵}12 34 60 77 19
877
3{+/⍵×⍺*(⊢-⍳)≢⍵}12 34 60 77 19
2680
⎕IO←0
3{+/⍵×⍺*⌽⍳≢⍵}12 34 60 77 19
2680

-Veli-Matti
Veli-Matti
 
Posts: 41
Joined: Sat Nov 28, 2009 3:12 pm


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