4 ms·

What language is that? AWK??

paulddraper 3y ago
It's got funny symbols, so I assume APL. [1] [1] https://en.wikipedia.org/wiki/APL_(programming_language) https://en.wikipedia.org/wiki/APL_(programming_language)
jodrellblank 3y ago
It's an APL sieve, for an input of 15 (primes up to 15) it does these steps: First 15 integers: ⍳ 15 ┌→──────────────────────────────────┐ │1 2 3 4 5 6 7 8 9 10 11 12 13 14 15│ └~──────────────────────────────────┘ 1 element dropped from the front of that: 1↓⍳15 ┌→────────────────────────────────┐ │2 3 4 5 6 7 8 9 10 11 12 13 14 15│ └~────────────────────────────────┘ That array stored in variable T: T←1↓⍳15 A table of outer-product multiplication, T by T: T∘.×T ┌→─────────────────────────────────────────────────┐ ↓ 4 6 8 10 12 14 16 18 20 22 24 26 28 30│ │ 6 9 12 15 18 21 24 27 30 33 36 39 42 45│ │ 8 12 16 20 24 28 32 36 40 44 48 52 56 60│ │10 15 20 25 30 35 40 45 50 55 60 65 70 75│ │12 18 24 30 36 42 48 54 60 66 72 78 84 90│ │14 21 28 35 42 49 56 63 70 77 84 91 98 105│ │16 24 32 40 48 56 64 72 80 88 96 104 112 120│ │18 27 36 45 54 63 72 81 90 99 108 117 126 135│ │20 30 40 50 60 70 80 90 100 110 120 130 140 150│ │22 33 44 55 66 77 88 99 110 121 132 143 154 165│ │24 36 48 60 72 84 96 108 120 132 144 156 168 180│ │26 39 52 65 78 91 104 117 130 143 156 169 182 195│ │28 42 56 70 84 98 112 126 140 154 168 182 196 210│ │30 45 60 75 90 105 120 135 150 165 180 195 210 225│ └~─────────────────────────────────────────────────┘ The elements of T which exist (are found) in the multiplication table, boolean result: T∊T∘.×T ┌→──────────────────────────┐ │0 0 1 0 1 0 1 1 1 0 1 0 1 1│ └~──────────────────────────┘ Showing that together with the input, 4 6 8 are found, 2 3 5 are not: T,[0.5]T∊T∘.×T ┌→────────────────────────────────┐ ↓2 3 4 5 6 7 8 9 10 11 12 13 14 15│ │0 0 1 0 1 0 1 1 1 0 1 0 1 1│ └~────────────────────────────────┘ Numbers not found in the multiplication table are prime, so invert the test result so primes get 1 and composites get 0: ~T∊T∘.×T ┌→──────────────────────────┐ │1 1 0 1 0 1 0 0 0 1 0 1 0 0│ └~──────────────────────────┘ Use that to 'compress' the input to keep things where the 1 positions are and drop things where the 0s are: (~T∊T∘.×T)/T ┌→────────────┐ │2 3 5 7 11 13│ └~────────────┘ You can play with it at https://tryapl.org/ https://tryapl.org/ using the bar at the top to enter the symbols.

It's got funny symbols, so I assume APL. [1] [1] https://en.wikipedia.org/wiki/APL_(programming_language) https://en.wikipedia.org/wiki/APL_(programming_language)

jodrellblank 3y ago

It's an APL sieve, for an input of 15 (primes up to 15) it does these steps: First 15 integers: ⍳ 15 ┌→──────────────────────────────────┐ │1 2 3 4 5 6 7 8 9 10 11 12 13 14 15│ └~──────────────────────────────────┘ 1 element dropped from the front of that: 1↓⍳15 ┌→────────────────────────────────┐ │2 3 4 5 6 7 8 9 10 11 12 13 14 15│ └~────────────────────────────────┘ That array stored in variable T: T←1↓⍳15 A table of outer-product multiplication, T by T: T∘.×T ┌→─────────────────────────────────────────────────┐ ↓ 4 6 8 10 12 14 16 18 20 22 24 26 28 30│ │ 6 9 12 15 18 21 24 27 30 33 36 39 42 45│ │ 8 12 16 20 24 28 32 36 40 44 48 52 56 60│ │10 15 20 25 30 35 40 45 50 55 60 65 70 75│ │12 18 24 30 36 42 48 54 60 66 72 78 84 90│ │14 21 28 35 42 49 56 63 70 77 84 91 98 105│ │16 24 32 40 48 56 64 72 80 88 96 104 112 120│ │18 27 36 45 54 63 72 81 90 99 108 117 126 135│ │20 30 40 50 60 70 80 90 100 110 120 130 140 150│ │22 33 44 55 66 77 88 99 110 121 132 143 154 165│ │24 36 48 60 72 84 96 108 120 132 144 156 168 180│ │26 39 52 65 78 91 104 117 130 143 156 169 182 195│ │28 42 56 70 84 98 112 126 140 154 168 182 196 210│ │30 45 60 75 90 105 120 135 150 165 180 195 210 225│ └~─────────────────────────────────────────────────┘ The elements of T which exist (are found) in the multiplication table, boolean result: T∊T∘.×T ┌→──────────────────────────┐ │0 0 1 0 1 0 1 1 1 0 1 0 1 1│ └~──────────────────────────┘ Showing that together with the input, 4 6 8 are found, 2 3 5 are not: T,[0.5]T∊T∘.×T ┌→────────────────────────────────┐ ↓2 3 4 5 6 7 8 9 10 11 12 13 14 15│ │0 0 1 0 1 0 1 1 1 0 1 0 1 1│ └~────────────────────────────────┘ Numbers not found in the multiplication table are prime, so invert the test result so primes get 1 and composites get 0: ~T∊T∘.×T ┌→──────────────────────────┐ │1 1 0 1 0 1 0 0 0 1 0 1 0 0│ └~──────────────────────────┘ Use that to 'compress' the input to keep things where the 1 positions are and drop things where the 0s are: (~T∊T∘.×T)/T ┌→────────────┐ │2 3 5 7 11 13│ └~────────────┘ You can play with it at https://tryapl.org/ https://tryapl.org/ using the bar at the top to enter the symbols.