The function 'exponential' in the 'hana_ml.algorithms.pal.random' module draws samples from an exponential distribution, with parameters for database connection, rate, number of random data, seed for random number generator, and thread ratio.
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Here is a Python code template for the `exponential` function in the `hana_ml.algorithms.pal.random` module:

```python
from hana_ml import ConnectionContext
from hana_ml.algorithms.pal.random import exponential

# Create a connection
cc = ConnectionContext(address='<address>', port='<port>', user='<user>', password='<password>')

# Set parameters
lamb = 1
num_random = 100
seed = None
thread_ratio = None

# Draw samples from an exponential distribution
res = exponential(conn_context=cc, lamb=lamb, num_random=num_random, seed=seed, thread_ratio=thread_ratio)

# Print the result
print(res.collect())
```

Please replace `<address>`, `<port>`, `<user>`, and `<password>` with your actual database connection details. You can also adjust the parameters `lamb`, `num_random`, `seed`, and `thread_ratio` as per your requirements.