How do I properly format the initial values passed to the parameter `start`

in the function `pymc.smc.sample_smc`

for Sequential Monte Carlo (SMC)?

To give a concrete example, let me consider the following code for Bayesian linear regression:

```
import pymc as pm
import numpy as np
def basic_model(observed_data):
array_sizes = np.array([size for (size, _) in observed_data])
array_costs = np.array([cost for (_, cost) in observed_data])
coefficient_sigma = 5
with pm.Model() as model:
coefficient0 = pm.HalfNormal(
"coefficient0", sigma=coefficient_sigma)
coefficient1 = pm.HalfNormal(
"coefficient1", sigma=coefficient_sigma)
predicted_bounds = coefficient0 + coefficient1 * array_sizes
observed_costs = pm.Normal("observed_costs", mu=predicted_bounds,
sigma=10, observed=array_costs)
return model
observed_data = [[1, 1], [2, 2], [4, 3], [8, 4], [
16, 7], [32, 10], [64, 13], [128, 17], [256, 18]]
init_nuts = {"coefficient0": 10,
"coefficient1": 10}
num_draws = 1000
num_chains = 4
init_smc = {"coefficient0_log__": np.full((num_draws, num_chains), 10),
"coefficient1_log__": np.full((num_draws, num_chains), 10)}
with basic_model(observed_data):
idata = pm.sample_smc(num_draws, start=init_smc,
chains=num_chains, random_seed=42)
```

When I run this code with PyMC v5.13.1, I get a warning `UserWarning: More chains (4) than draws (1). Passed array should have shape (chains, draws, *shape)`

. I believe the warning stems from the improper shape/format of the initial values `init_smc`

I pass to the function `pm.sample_smc`

. Here, `init_smc`

is a dictionary mapping variable names (i.e., `coefficient0_log__`

and `coefficient1_log__`

) to numpy arrays of shape `(num_draws, num_chains)`

.

I couldnâ€™t find documentation on what the initial valuesâ€™ format should be. Does anyone know by any chance how to resolve this issue? Thanks a lot in advance!