[ncl-talk] Segmentation fault: Read variables with different time units using addfiles

[David Brown]

Hi Hoffman,
I am looking into this issue now. Thank you for providing scripts that
illustrate the problem perfectly without the need for any data files.
My apologies for taking so long to respond.
 -dave

On Tue, Jul 5, 2016 at 1:56 PM, Hoffman Cheung <hoffmancheung at gmail.com> wrote:
> Hello,
>
> For some CMIP5 models, they use different time units for different files of
> the same parameter (say "days since 1950-1-1" for the first file; "days
> since 1960-1-1" for the second file, and so on). For data analysis, it is
> convenient to use addfiles to read the parameter at different files (say,
> read all summer months using one simple line).
>
> The function addfiles works perfectly for the datasets when their files have
> the same time unit. However, when I apply the same method for reading the
> files have different time units, segmentation fault always occurs when the
> program neither (i) read all files nor (ii) read one file.
>
> I checked the program, and I think the following is main points:
>
> First, when addfiles is used for reading all files, it works perfectly even
> if the files have different time units. The time unit of these files would
> be the same as the first file.
>
> Example:
> if the positions 10 and 11 are from two separate files, and
> time(10) = 10  ; unit: days since 1950-1-1
> time(11) = 0    ; unit: days since 1951-1-1
>
> f = addfiles(filesIN,"r")
> t = f[:]->time
>
> Then, if the program prints time(10:11), then the output is
> [0] 10
> [1] 365
>
> Second, when addfiles is used for reading more than one file but not all
> files, the time unit would not be changed:
>
> Same as the above example, but I use the following line to read time
>
> t = f[:]->time(10:11)
>
> Then, if the program prints time, then the output is:
> [0] 10
> [1] 0
>
> Segmentation fault occurs when the program reads more time
>
> I have attached two programs for simply checking how it works for reading
> files with different time units. For the first program
> ("d01_create_file.nc"), it generates 20 files with different time units. For
> the second program, it reads the files generated from the first program. I
> have commented the part that leads to segmentation fault.
>
> Definitely, I can solve this problem by first changing the time units of
> these files. Or I can use alternative methods to carry out my analyses (I
> think I encountered the same problem several years ago, but I did not report
> the problem). However, it will be great if this issue can be solved.
>
> Thank you for the reply!
>
> Best Regards,
> Hoffman
>
>
>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>