Anonymous user
Talk:Sieve of Eratosthenes: Difference between revisions
→Problem found in first Erlang example.
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Line 287:
Problem found by user Poetaster . I just moved the report here. --[[User:Paddy3118|Paddy3118]] ([[User talk:Paddy3118|talk]]) 06:53, 19 September 2015 (UTC)
corrected version:
<lang Erlang>
-module( sieve_of_eratoshenes ).
-export( [primes_upto/1] ).
primes_upto( N ) ->
Ns = lists:seq( 2, N ),
Dict = dict:from_list( [{X, potential_prime} || X <- Ns] ),
{Upto_sqrt_ns, _T} = lists:split( erlang:round(math:sqrt(N)), Ns ),
{N, Prime_dict} = lists:foldl( fun find_prime/2, {N, Dict}, Upto_sqrt_ns ),
lists:sort( dict:fetch_keys(Prime_dict) ).
find_prime( N, {Max, Dict} ) -> find_prime( dict:find(N, Dict), N, {Max, Dict} ).
find_prime( error, _N, Acc ) -> Acc;
find_prime( {ok, _Value}, N, {Max, Dict} ) when Max > N*N ->
{Max, lists:foldl( fun dict:erase/2, Dict, lists:seq(N*N, Max, N))};
find_prime( {ok, _Value}, _, R) -> R.
</lang>
== R code error ==
Line 324 ⟶ 346:
return(list[A[-1]]) #remove 1
}
:Corrected. Some oddities in your own program: once you have computed i^2, no need to compute sqrt(n), just compare i^2 and n. Also, no need for 'list', use the 'which' function. You may replace 'break' with 'return' and 'repeat' with a 'for' loop since you are incrementing the index 'i' at the end of each loop. Last, but not
== Pari/GP script ==
The first script uses "forprime(p=2,sqrt(lim)" which seems contrary to the task assignment.[[User:Billymacc|Billymacc]] ([[User talk:Billymacc|talk]]) 03:01, 4 May 2021 (UTC)
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