Re: Issue with ParallelTable and AstronomicalData
- To: mathgroup at smc.vnet.net
- Subject: [mg116226] Re: Issue with ParallelTable and AstronomicalData
- From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
- Date: Mon, 7 Feb 2011 06:06:39 -0500 (EST)
Hi,
gives the same results here (Linux-x86-64) but this anyway a very bad
idea:
Say you move from New York to Germany and you send all your stuff on a
big ship to reassemble it after two weeks journey in your new flat in
Germany. Pretty long time you think, but you come up with a brilliant
idea: Lets to all this work in parallel!
So you send not only one ship, but say 4 ships and distribute you stuff
on them and you reassemble not alone but with 3 other workers..
Do you see where the bottleneck is and why this won't be really faster?
I'm pretty sure that AstronomicalData[..] accesses your hard-drive to
fetch the data and if so, you shouldn't expect a speedup by a parallel
execution.
Cheers
Patrick
On Sat, 2011-02-05 at 05:44 -0500, Thomas Melehan wrote:
> Group:
>
> The the only difference in the following two modules is the use of
> ParallelTable in one and Table in the other. For some strange reason
> they give different results. I tried to DistributeDefinitions
> [AstronomicalData], with no impact. Any ideas?
>
>
> I am using Mathematica 8 on Mac OSX 10.6.6
>
>
>
>
> Module[{date, month, day, =CE=B1, =CE=B3Sun, testData},
>
> ParallelTable[
>
> date = DateList[{2010, ToExpression[month], ToExpression[day],
> ToExpression[hour]}, TimeZone -> -5];
> =CE=B1 = Max[AstronomicalData["Sun", {"Altitude", date}, TimeZone -> -5] ,
> 0] Degree ;
> =CE=B3Sun = AstronomicalData["Sun", {"Azimuth", date}, TimeZone -> -5] Degree;
> testData =
> AstronomicalData["Sun", {#, date}] Degree & /@ {"Azimuth", "Altitude"};
>
> {date, =CE=B3Sun, =CE=B1, testData, month, day, hour}
>
> , {month, {"01"}}, {day, {"15"}}, {hour, {"08", "09"}}]
>
> ]
>
>
> Module[{date, month, day, =CE=B1, =CE=B3Sun, testData},
>
> Table[
>
> date = DateList[{2010, ToExpression[month], ToExpression[day],
> ToExpression[hour]}, TimeZone -> -5];
> =CE=B1 = Max[AstronomicalData["Sun", {"Altitude", date}, TimeZone -> -5] ,
> 0] Degree ;
> =CE=B3Sun = AstronomicalData["Sun", {"Azimuth", date}, TimeZone -> -5] Degree;
> testData =
> AstronomicalData["Sun", {#, date}] Degree & /@ {"Azimuth", "Altitude"};
>
> {date, =CE=B3Sun, =CE=B1, testData, month, day, hour}
>
> , {month, {"01"}}, {day, {"15"}}, {hour, {"08", "09"}}]
>
> ]
>