in activity selection we sort on finish time of activities and then apply the constraint that no two activities can overlap.i want to know whether can we do it by sorting on start time andthenseeing if activities do not overlap
i was going through http://www.geeksforgeeks.org/dynamic-programming-set-20-maximum-length-chain-of-pairs/
this link has a dynamic programming solution for finding maximum length chain of pairs of numbers .. this according to me is another formulation of activity selection problem but i have searched on net and as also have read cormen but everywhere they ask to sort on finish times ...
i guess it shouldnt matter on what times(start or finish)we sort but just want to confirm the same
In greedy algorithm we always try to maximize our result. Thus, In activity selection we try to accommodate as many processes as we can in a given time interval without overlapping each other.
If you sort on start time then your solution might not be an optimal solution. Let's take an example,
Processes start Time Finish Time
A 1 9
B 3 5
C 6 8
Sorted on start Time:
If you execute process A because it starts at the earliest no other process can be executed because they will overlap. Therefore, for a given time interval you can only execute one process.
Sorted on Finish Time:
If you execute process B because it ends at the earliest you can execute process C after that. Therefore, for a given time interval you can execute two processes.
Related
I am trying to build a test plan in JMeter based on a specific thread time series.
For example, I know that at time x, there are n(x) users, and at time x+t, there are n(x+t) users, and so on. The issue is that the number of users has to be updated for t ~= 500ms, and the thread number is in a range of 20 - 200.
Also, ideally, I would like to add and remove threads for the next time slot from the active threads instead of building new threads every time to save resources.
I was trying different tricks to simulate this scenario:
Using execution of Thread Groups sequentially, you can set the duration lifetime but in seconds, every thread will be killed after the specific time slot and recreated in the following thread group.
Using the ultimate thread group, you can define your series of threads for each time interval but still in seconds, and it goes to generate new threads for each timeslot.
In both cases, if you fill the duration box with a value of 0.5, it seems not to recognize it or not work fine.
Do you have any suggestions on how to implement this scenario?
I'm not aware of any Thread Group which has milliseconds precision, but you can try to extrapolate it, for example if you need to add 100 users in 500 ms you can try kicking off 200 users in 1 second and it should be more or less desired load pattern.
The only implementation of thread pool pattern I'm aware of is Throughput Shaping Timer in combination with the Concurrency Thread Group via Feedback Function
And last but not the least there is a possibility to start new threads and stop running ones from JSR223 Test Elements like:
ctx.getThreadGroup().addNewThread(0, ctx.getEngine()) // starts new thread and returns its instance
ctx.getThreadGroup().stopThread('name of the thread', false) // stops the given thread, 2nd argument is for force stop
Consider you are running simulations and each simulation writes results to a output.txt file. I want to run thousands of simulations using multithreading, while doing that even though if i use locking, unlocking, i was still having errors when multiple threads access to the file at the same time.
To solve this, I am going to add result texts to a query that stores them. That is, each thread will add result to this query instead of writing it to the output.txt file. And in the end, i'll take stored texts from query and write to output.txt
My question here is: whenever multiple threads are adding such items to a query, do you think an error might happen in the end, like, missing simulation ? I've come up to this question because whenever you increase single value by multithreads, that value will not be incremented as much as you want if you don't be careful. (i.e, in a multithreaded for loop, add +1 to previously declared int a for 1000 times; then in the end, a will not be 1000 (ofc this can be prevented by other things))
I'm new with multi-threading in Matlab so I guess that what I need to do will be simple for anyone with a little experience in it.
I have two functions f1 and f2 such that:
f1 - runs about 10 seconds and returns accurate results.
f2 - return estimated results immediately.
Both functions get the same input and return the same output (but in f1 the output is more accurate).
The functions get new inputs all the time and run constantly.
I want to run the functions in two different threads so that the user will never need to wait.
and every time one of them finishes, the other one uses its results.
The goal is to get more accurate results than running f2 all the time. Running f1 all the time is the optimal solution but then the user needs to wait 10 seconds each time. So I want to combine the two functions and to get something in the middle.
What is the best way to implement the above?
I read about batch but I'm not sure it's what I need (at least I didn't find how to do the above with batch).
Can you just lead me with the relevant functions and I'll read about them and learn how to use them?
Thanks
I have a Large-Scale Gradient Descent optimization problem that I am running using Matlab. The code has got two parts:
A Sequential update part that fires every iteration that updates the parameter vector.
A validation error computation part that fires every 10 iterations or so using the parameter value at the end of the corresponding iteration in which its fired.
The way that I am running this now is to do (1) and (2) sequentially. But (2) takes a lot of time and its not the core part of my routine - I made it just to check the progress and plot the error of my model. Is it possible in Matlab to run (2) in a parallel manner to (1) ? Please note that (1) cannot be run in parallel since it performs sequential update. So a simple 'parfor' usage is not a solution, unless there is a really smart way of doing that.
I don't think Matlab has any way of multi-threading outside of the (rather restricted) parallel computing toolbox. There is a work over which may help you though:
Open 2 sessions of Matlab, sessions A and B (or instances, or workspaces, however you call it)
Matlab session A:
Calculate the 10 iterations of your sequential process (1)
Saves the result in a file (adequately and uniquely named)
Goes on to calculate the next 10 iterations (back to the top of this loop basically)
In parralel:
Matlab session B:
Check periodically for the existence of the file written by process A (define a timer that will do that at the time interval which make sense for your process, a few seconds or a few minutes ...)
If the file exist => load it then do the validation computation (your process (2)) and display/report the results.
note: This only works if process (1) doesn't need the result of process (2) to run its iterations, but if it is the case I don't know how you could parallelise anyway.
If you have multiple cores on your machine that should run smoothly, if you have a single core then the 2 sessions will have to share and you will see a performance impact.
I have 3 different jobs set up in crontab (call them jobA, jobB, jobC) that run at different intervals and start at different times during the day. For example, jobA runs once per hour at 5 mins past the hour, jobB runs every 30 mins at 9 and 39 mins past the hour, and jobC runs every 15 mins. They are not dependent on each other, but for various reasons they can NOT be running at the same time.
The problem is that sometimes one of the jobs takes a long time to run and another one starts before the first one is done, causing issues.
Is there some way to queue or spool these jobs so that one will not start until the current running one has finished? I tried using this solution but this does not guarantee that the pending jobs will resume in the same order they were supposed to start. A queue would be best, but I cannot find anything about how to do this.
You can't do that using cron. Cron is used to run a specific command at specific time. You can do it by the solution you proposed, but that adds a lot more complexity.
I suggest, writing/coding the requirement in high level language like java and use a mutil-thread program to achieve what you need.
Control-m is another scheduling software, with a lot of other features as well. You would be able to integrate the above use-case in it.