Free fall

Example 2: Velocity due to gravtity in free fall¶

The second example calculates the velocity of an object falling from the sky (without air resistance).

The standard gravity on earth is 9.81 m*s^(-2). Multiplicated by the fall time, we will get the velocity of the object after that time.

If you like equations more, you might recognize these from your physics class: $$ v = g \cdot t $$

In regular python code that you run locally it would look like this:

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standard_gravity = 9.81
time = 200.

velocity = standard_gravity * time
print(f"Velocity after {time} seconds is {velocity} m/s.")

Now we want to be able to share that functionality via the lmrtfy web API. All we have to do is decide which variables are considered to be an input and a result of the computation:

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from lmrtfy import variable, result

standard_gravity = 9.81
time = variable(200., name="time", min=0, max=1000, unit="s")

velocity = result(standard_gravity*time, name="velocity", min=0, max=9810, unit="m/s")
print(f"Velocity after {time} seconds is {velocity} m/s.")

Now run $ python examples/velocity_from_gravity/calc_velocity.py to generate the required profile. This way you can also check if your code is actually working the way you expect it.

Deploying the script¶

To deploy, you simply run $ lmrtfy deploy examples/velocity_from_gravity/calc_velocity.py --local. Do not stop that process, because than you will not be able to submit a job.

Calling from code¶

Calling free_fall_lmrtfy by code as easy as it was for the first example.

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import time
from lmrtfy.functions import catalog

job = catalog.<your_namespace>.free_fall_lmrtfy(time=100.0) # (1)!

if job:
    while not job.ready:
        time.sleep(1)

    print(job.results)

1. <your_namespace> is your private namespace on LMRTFY, which is typically your nickname. Available namespaces are shown when importing catalog or when calling catalog.update().

Calling from CLI¶

Open a new terminal in the same directory and run $ lmrtfy submit <profile_id>. The profile_id has been printed in the lmrtfy deploy step. This does not work right out of the box, because you need to specify a JSON file that contains the input parameters for your job. A template for that JSON should have been printed in the CLI.

Create such a JSON file and name it input.json and put values of the correct type into the values (no type conversion is happening in the API, so if float is required, you cannot input an int). Alternatively, use the provided input.json in examples/free_fall/input.json:

{
  "argument_values": {
    "time": 6.0
  },
  "argument_units" : {
    "time": "s"
  }
}

Now run $ lmrtfy submit <profile_id> examples/free_fall/input.json. You will receive a job_id which we will shortly need to fetch the results after they are computed.

After your job has run, you can get the results by running $ lmrtfy fetch <job_id> <path to store results>.

The results are downloaded and stored inside the specified path within a directory that has the job_id as its name.