Interpreting the results of a qualitative experiment
Part 1: Standard screen output
Hello and welcome to this video,
which follows on from the video about
setting up a qualitative experiment
with the Ariane program.
The objectives of this module
are to learn how to set up
a new qualitative experiment
from an earlier experiment
and how to analyse the results
that appear on the screen during runtime.
To do this, I go back in the directory
where I did my first qualitative experiment,
experiment 0 ('Exp0') here.
I'll create a second directory:
'Exp1', in which I will put
a new experiment.
Here is the description of this experiment 1.
We have two recordings,
'record 1' and 'record 2'.
Each of these corresponds to 180 days.
I remind you that, in the Namelist file,
'tunit' = 86,400, so 1 day * 180
for 180 days per recording.
We will position four particles in this recording.
Particle 1 will start
at the very beginning of record 1.
Particles 2 and 4 will start
midway through record 1
and particle 3
will start midway through record 2.
The position of these particles will be specified
in the file 'initial_positions.txt'.
Then, in Namelist, we will ask to record
six points along the trajectories
of these four particles.
For this we will adjust
the three 'delta_t' variables,
with 'delta_t' = 86,400, so 1 day.
The frequency is 30
so, every 30 days, we ask for
a position along our trajectory.
And we'll ask for six positions.
This is shown here for particle 1
by six recordings (red crosses).
Then, we will integrate
in the forward (or positive) direction of time.
I go back to my directory.
I go into 'Exp1',
in which I have created
a symbolic link to the Ariane executable
as you already know how to do.
I copied the Namelist file from experiment 0,
making some changes to the parameters,
especially during the recording of the trajectory.
In the previous experiment, we asked for
12 records, here there are only six.
I have also copied the file 'initial_positions.txt'
from experiment 0,
and changed the positions of the particles
as I explained earlier.
Here we see the positions in time
(which I highlight here)
for particles 1, 2, 3 and 4.
I will now run Ariane
in the directory.
As this is a fairly simple experiment,
the execution is very fast.
I'll go back and we'll look at
the content displayed on the screen.
Here we find the launch of the Ariane command.
Then, we have a header that respecifies
the version of Ariane we are using.
This is version 2.3.0_02.
A remark about the CeCILL license
for the Ariane program.
We have some information
about the machine you are using.
Then we find all the Namelist parameters
of the Ariane application.
The set of parameters of Ariane
are much more numerous
than just the parameters defined in Namelist.
Here we have all the details:
we find the parameters you set for the Namelist file.
In particular, the location of your data
current 'U', current 'V', etc.
We also have the information on the grid
and the qualitative information.
We are reminded that this is a qualitative experiment.
Otherwise it would be marked 'quantitative' here instead.
Then, Ariane reads the grid of your model
in the directory you specified.
The application displays some statistics:
the maximum and minimum readings in the file.
For example, here, for longitudes,
then for latitudes,
for the depths,
and for the scaling factors that allow us
to pass from currents to transport.
We have information about the mask,
with '1' when we are on the ocean
and '0' when on land.
Then, Ariane tells us
from which recording
it starts to read the currents.
We positioned a particle
at the very beginning of the first recording,
so Ariane will start with this first recording.
But imagine that the particles
started at the tenth recording,
Ariane would only start reading the data
from the tenth recording.
Then Ariane will create a very important file,
which we will see in another video:
'ariane_trajectories_qualitative.nc',
in which information will be stored
on the initial and final positions of the particles,
as well as those along the trajectories,
according to the frequency you set.
Here we asked to track four particles
and we asked for six outputs.
We see here that we have seven,
because Ariane also saves the initial position.
The initial position + six recordings
give us seven pieces of information.
Here we have the details of the different variables
that will be recorded in the NetCDF file.
Let's go into the main part of the program.
This is a loop that runs throughout
the different recordings available
in the data you specified in the Namelist file.
Here we have only two recordings.
Ariane will read the first recording,
for our four particles.
Ariane first reads the current
and gives us simple statistics like
the maximum and minimum currents.
It is interesting to check that the current
is as you expect.
Then, it gives some information
on the transport for this current 'U'.
It does the same for the meridian component of the current 'V'
and for the vertical component of the current,
which is available here.
It will save some information,
then read the second recording
and so on with the currents 'U', 'V' and 'W'.
We only had two recordings
so our four particles have been integrated.
Here we have some information
specific to this particular case:
a particle, particle 4,
has left our geographical domain.
This particle has reached
the boundaries of the domain in the north.
The interpretation of these results
will be the subject of another video.
Ariane then records the information
about the positions of the particles
along this trajectory.
We have some statistical information
on the memory and Ariane finishes.
In general, we recommend
saving the information
displayed on the screen into a file.
I'll go over
the commands available
under linux, depending on your shell environment.
If you are in 'bash' you will have to type
these instructions to save
the information shown onscreen to a file.
The file here will be 'ariane_output.txt',
but you can put whatever file name you want.
If you are in 'csh' or 't/csh',
the command line will be this one.
As I am in 'bash',
I will use the command line here:
'./ariane',
then I direct the standard output '>'
on the screen into a file,
which I will name 'output.txt'.
You can name it anything you like.
These last four characters '2>&1' will send
the errors on the screen into the output file.
Then I run my application.
All information on the screen
gets saved in a file.
This file can then be viewed
and we again see all the information
that we had on the screen.
This will be even more interesting
when you do some realistic experiments
with a large number of recordings.
Ariane has a lot to say!
So, in this file, we find
what was on the screen:
– the parameters of the Namelist file,
– simple statistics describing the grid,
– the creation of the main NetCDF file,
– the main read loop
of the current components,
– and, lastly, the writing of the trajectory.
In this video, we have seen how
to create a new qualitative experience
from a previous experiment
and how to interpret the results
that appear on the screen when
you run the Ariane executable.
Next, we'll see how to
interpret the results in the file
'ariane_trajectories_qualitative.nc',
in which we will find the whole set
of the trajectories of our particles.
Thank you!