# Concatenate two trajectories

**URL:** <https://gromacs.bioexcel.eu/t/concatenate-two-trajectories/3723>\
**Category:** User discussions\
**Tags:** mdrun\
**Created:** [February 22, 2022, 8:03am UTC](https://gromacs.bioexcel.eu/t/concatenate-two-trajectories/3723 "2022-02-22T08:03:50Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![shivanigupta](https://avatars.discourse-cdn.com/v4/letter/s/c2a13f/32.png) [@shivanigupta](https://gromacs.bioexcel.eu/u/shivanigupta)\
**Post date:** [February 22, 2022, 8:03am UTC](https://gromacs.bioexcel.eu/t/concatenate-two-trajectories/3723/1 "2022-02-22T08:03:50Z")

</div>

GROMACS version:  
GROMACS modification: Yes/No  
Here post your question I have concatenated two trajectories but teh output file is terminating at 81 ns. But the log file clearly explains that teh simulation is completed till 500ns.

commmand used- gmx\_mpi trjcat -f md\_0\_1.trr traj.trr -o fixed.trr

```
      md_0_1.trr 0.000 ps 10.000 ps
              old.trr 24980.000 ps 10.000 ps

```

Error got - Continue writing frames from md\_0\_1.trr t=0 ps, frame=0  
 → frame 2490 time 24900.000 ps → frame 2000 time 20000.000 ps  
Reading frame 0 time 24980.000  
lasttime 24970

Continue writing frames from old.trr t=24980 ps, frame=2498  
 → frame 8100 time 81000.000 ps → frame 7500 time 75000.000 ps

Last frame written was 8101, time 81010.000000 ps

gcq#424: “Consistently separating words by spaces became a general custom about the tenth century A.D., and lasted until about 1957, when FORTRAN abandoned the practice.” (Sun FORTRAN Reference Manual)

Kindly help and thanks in advance .