## Decode problem

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### Decode problem

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: 44
Joined: Mon Apr 09, 2018 8:37 am

### Re: Decode problem

Perhaps this will explain it better:
`      +/ 12 34 60 77 19 × 2*4 3 2 1 0877`

-Veli-Matti
Veli-Matti

Posts: 56
Joined: Sat Nov 28, 2009 3:12 pm

### Re: Decode problem

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: 44
Joined: Mon Apr 09, 2018 8:37 am

### Re: Decode problem

This might give some kind of insight as well:
`      ⎕IO←1      0⊥12 34 60 77 1919      0{⍺⊥⍵}12 34 60 77 1919      1{+/⍵×⍺*⌽¯1+⍳≢⍵}12 34 60 77 19202      2{+/⍵×⍺*(≢⍵)-⍳≢⍵}12 34 60 77 19877      3{+/⍵×⍺*(⊢-⍳)≢⍵}12 34 60 77 192680      ⎕IO←0      3{+/⍵×⍺*⌽⍳≢⍵}12 34 60 77 192680`

-Veli-Matti
Veli-Matti

Posts: 56
Joined: Sat Nov 28, 2009 3:12 pm

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