Thank you again for your answers and clarifications. Here you can see the benefit that I got in a little example:

Thank you very much for your answers, now it works!!! In this example, I can use 4 processors of the package Grid in order to write into 4 multiple files! And, I must use Fortran Code Generation, otherwise I get an error for the command "cat" for creating the strings... you can see this in the code setting BBB=2.

Now, I also want to check the benefits in reducing the elapsed time, I'll let you know!

I upload the working Maple18 script, if it can be helpful for someone else:

Myworksheet_serialcomput_paralleloutput_GRID[MaplePrimes_Forum].mw

 

@acer Ok, sorry. This is my worksheet, running with option 1B, when rows-1 >1000 (therefore attempting to write into multiple files) 

Myworksheet_serialcomput_parallelotput.mw

@Carl Love Please, could you please explain me what do you mean with multiple disk drives? I'm writing into one folder of  the local hard disk C:\... I've got Windows10 Home, and the hard disk is a Toshiba mq01abd100, driver version=10.0.17763.1

However, this doesn't solve the problem of the errors that I get from Maple when trying to write in parallel?

Noone trying to answer to me?

Thanks

Then, should I look for the thread-safe functions here (https://www.maplesoft.com/support/help/Maple/view.aspx?path=index/threadsafe/version) , and use only functions from that list inside my "new_print_F" function? Will that be enough?

First of all, in Maple18 there aren't so many thread-safe functions. There aren't the functions that I need. Does it mean that it's impossible to write output files in parallel, in Maple18?

Should I move to Maple15? Will my code be portable?

Thanks