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Why is ParallelDo slower than Do?
The 2019 Stack Overflow Developer Survey Results Are InInternal`Bag inside CompileWhy won't Parallelize speed up my code?ParallelTable 70 times slower on 16 cores than Table on single coreWhy is ParallelMap way slower than MapParallelTable slower than Table in the presence of an Association?How to make the ProgressIndicator for ParallelDo more efficientParallel calculation is 5 times slower than the non-parallel oneParallelTable much slower than Table on RandomReal with arbitrary precisionParallelDo with doubly-indexed iteratorsClearAttributes in ParallelDoWriting to file with ParallelDoParallelDo gives different solution to Eigensystem
$begingroup$
I have problems to write parallel code in mathematica.
Why is
candidates = {};
SetSharedVariable[candidates];
Do[
ParallelDo[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
slower than the non parallel version
candidates = {};
Do[
Do[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
?
parallelization
edited 14 hours ago
corey979
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I have problems to write parallel code in mathematica.
Why is
candidates = {};
SetSharedVariable[candidates];
Do[
ParallelDo[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
slower than the non parallel version
candidates = {};
Do[
Do[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
?
parallelization
edited 14 hours ago
corey979
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
1
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago
add a comment |
$begingroup$
I have problems to write parallel code in mathematica.
Why is
candidates = {};
SetSharedVariable[candidates];
Do[
ParallelDo[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
slower than the non parallel version
candidates = {};
Do[
Do[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
?
parallelization
edited 14 hours ago
corey979
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I have problems to write parallel code in mathematica.
Why is
candidates = {};
SetSharedVariable[candidates];
Do[
ParallelDo[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
slower than the non parallel version
candidates = {};
Do[
Do[
eq = RandomReal[] + RandomReal[];
AppendTo[candidates, eq]
, {j, 1, 1000}]
, {i, 1, 10}]
?
parallelization
parallelization
edited 14 hours ago
corey979
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 14 hours ago
corey979
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 14 hours ago
corey979
20.9k64282
edited 14 hours ago
corey979
20.9k64282
edited 14 hours ago
corey979
20.9k64282
20.9k64282
asked 15 hours ago
Matthias HellerMatthias Heller
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 15 hours ago
Matthias HellerMatthias Heller
283
asked 15 hours ago
Matthias HellerMatthias Heller
283
283
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Matthias Heller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
1
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago
add a comment |
$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
1
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago
$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
1
1
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
Because managing write access to shared memory is expensive: Subprocesses have to wait until they are granted write access (because another process uses that ressource).
Moreover, it is in general more efficient to use Parallel only upon the most outer loop construct.
By the way: Using Append and AppendTo are the worst methods to build a list, because they involve a copy of the full list each time another element is appended. Instead of complexity $O(n)$ for a list of $n$ elements, you get an implementation of complexity $O(n^2)$. Better use Table or, if you don't know how long the list is about to get, use Sow and Reap. Internal`Bag is a further option, and it is even compilable.
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
$endgroup$
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not useParallelat all, but ratherCompiled code.
$endgroup$
– Henrik Schumacher
14 hours ago
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Because managing write access to shared memory is expensive: Subprocesses have to wait until they are granted write access (because another process uses that ressource).
Moreover, it is in general more efficient to use Parallel only upon the most outer loop construct.
By the way: Using Append and AppendTo are the worst methods to build a list, because they involve a copy of the full list each time another element is appended. Instead of complexity $O(n)$ for a list of $n$ elements, you get an implementation of complexity $O(n^2)$. Better use Table or, if you don't know how long the list is about to get, use Sow and Reap. Internal`Bag is a further option, and it is even compilable.
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
$endgroup$
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not useParallelat all, but ratherCompiled code.
$endgroup$
– Henrik Schumacher
14 hours ago
add a comment |
$begingroup$
Because managing write access to shared memory is expensive: Subprocesses have to wait until they are granted write access (because another process uses that ressource).
Moreover, it is in general more efficient to use Parallel only upon the most outer loop construct.
By the way: Using Append and AppendTo are the worst methods to build a list, because they involve a copy of the full list each time another element is appended. Instead of complexity $O(n)$ for a list of $n$ elements, you get an implementation of complexity $O(n^2)$. Better use Table or, if you don't know how long the list is about to get, use Sow and Reap. Internal`Bag is a further option, and it is even compilable.
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
$endgroup$
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not useParallelat all, but ratherCompiled code.
$endgroup$
– Henrik Schumacher
14 hours ago
add a comment |
$begingroup$
Because managing write access to shared memory is expensive: Subprocesses have to wait until they are granted write access (because another process uses that ressource).
Moreover, it is in general more efficient to use Parallel only upon the most outer loop construct.
By the way: Using Append and AppendTo are the worst methods to build a list, because they involve a copy of the full list each time another element is appended. Instead of complexity $O(n)$ for a list of $n$ elements, you get an implementation of complexity $O(n^2)$. Better use Table or, if you don't know how long the list is about to get, use Sow and Reap. Internal`Bag is a further option, and it is even compilable.
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
$endgroup$
Because managing write access to shared memory is expensive: Subprocesses have to wait until they are granted write access (because another process uses that ressource).
Moreover, it is in general more efficient to use Parallel only upon the most outer loop construct.
By the way: Using Append and AppendTo are the worst methods to build a list, because they involve a copy of the full list each time another element is appended. Instead of complexity $O(n)$ for a list of $n$ elements, you get an implementation of complexity $O(n^2)$. Better use Table or, if you don't know how long the list is about to get, use Sow and Reap. Internal`Bag is a further option, and it is even compilable.
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
edited 14 hours ago
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
answered 15 hours ago
Henrik SchumacherHenrik Schumacher
59.9k582167
59.9k582167
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not useParallelat all, but ratherCompiled code.
$endgroup$
– Henrik Schumacher
14 hours ago
add a comment |
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not useParallelat all, but ratherCompiled code.
$endgroup$
– Henrik Schumacher
14 hours ago
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
$begingroup$
Thanks, that actually helped a lot. I just dont understand how to use Sow and Reap to avoid Append To be more specific: instead of ParallelDo I use now ParallelTable: eq = ParallelTable[ FNumeric[ SetPrecision[N[monlistnumeric[[i]] + monlistnumeric[[j]], 20], 10]] , {j, jj}]; FNumeric is a function, that returns either 0 or a value I want to store. I then do eq = DeleteCases[eq, 0]; candidates = Join[candidates, eq]; Is there a more efficient way to do this?
$endgroup$
– Matthias Heller
15 hours ago
2
2
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not use
Parallel at all, but rather Compiled code.$endgroup$
– Henrik Schumacher
14 hours ago
$begingroup$
@MatthiasHeller, you're welcome. How is this new code related to your post? You should consider a new post with your real problem and all relevant data. I may have a look. In general, depending on the details, there are various ways to perform the computation efficiently; these way might not use
Parallel at all, but rather Compiled code.$endgroup$
– Henrik Schumacher
14 hours ago
add a comment |
Matthias Heller is a new contributor. Be nice, and check out our Code of Conduct.
Matthias Heller is a new contributor. Be nice, and check out our Code of Conduct.
Matthias Heller is a new contributor. Be nice, and check out our Code of Conduct.
Matthias Heller is a new contributor. Be nice, and check out our Code of Conduct.
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$begingroup$
I reverted your post to before the edit because it looks like a different question (like Henrik said in his comment). Note, however, that if you ask it in precisely such form it will be likely closed due to not enough info: you need to provide the minimal working example, not through some undefined functions into a piece of code that no one will be able to run and test.
$endgroup$
– corey979
14 hours ago
1
$begingroup$
See here mathematica.stackexchange.com/a/48296/12 I suggest you don't use SetSharedVariable until you get quite fluent in using the parallel tools. It effectively "unparallelizes" your code.
$endgroup$
– Szabolcs
13 hours ago