Hi, I am trying to save and load a trained model for posterior predictions with a model that contains a BART RV. I am running into multiple issues that is making this task seem not possible. If anyone could provide me with some input on what I might be doing wrong I would appreciate it.

```
from pathlib import Path
import arviz as az
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
import pymc as pm
import pymc_bart as pmb
import cloudpickle as cpkl
print(f"Running on PyMC v{pm.__version__}")
print(f"Running on PyMC-BART v{pmb.__version__}")
```

VERSION 5 for both PYMC and PYMC-BART

Using the bikes example for simplicity.

```
try:
bikes = pd.read_csv(Path("..", "data", "bikes.csv"))
except FileNotFoundError:
bikes = pd.read_csv(pm.get_data("bikes.csv"))
features = ["hour", "temperature", "humidity", "workingday"]
X = bikes[features]
Y = bikes["count"]
xt = X[0:10]
yt = Y[0:10]
```

Baseline model

```
with pm.Model() as model_bikes:
xdata = pm.MutableData("xdata", X)
a = pm.Exponential("a", 1)
mu_ = pmb.BART("mu_", xdata, np.log(Y), m=20)
mu = pm.Deterministic("mu", pm.math.exp(mu_))
y = pm.NegativeBinomial("y", mu=mu, alpha=a, observed=Y, shape=xdata.shape[0])
idata_bikes = pm.sample(random_seed=99, draws=100, tune=100, compute_convergence_checks=False)
idata_bikes
```

Used the clouldpickle to save the trace. I was having some weird issues with to_netcdf (basically the file stayed open and I couldn’t overwrite it when trying things out, it was easier to just pickle).

```
with open('test4.pkl', mode='wb') as file:
cpkl.dump(idata_bikes, file)
with open("test4.pkl", mode="rb") as file:
idata4 = cpkl.load(file)
```

Test the posterior predictions on the baseline model using the baseline idata and the saved/reload idata.

Both work fine.

It also works to set the new data when using the baseline model.

```
with model_bikes:
pm.set_data({"xdata": xt})
post1 = pm.sample_posterior_predictive(idata_bikes, var_names=["mu", "y"])
with model_bikes:
pm.set_data({"xdata": xt})
post2 = pm.sample_posterior_predictive(idata4, var_names=["mu", "y"])
```

This is where things start to get difficult. Based on other examples I should be able to create a new model (untrained) and then get posterior predictions with the saved traced.

New model

Input data is the same as the input data in the baseline model.

```
with pm.Model() as model2:
xdata2 = pm.MutableData("xdata", X)
a2 = pm.Exponential("a", 1)
mu_2 = pmb.BART("mu_", xdata2, np.log(Y), m=50)
mu2 = pm.Deterministic("mu", pm.math.exp(mu_2))
y2 = pm.NegativeBinomial("y", mu=mu2, alpha=a2, observed=Y, shape=xdata2.shape[0])
```

NOTE I named the new variable with suffix 2 because I thought there maybe was a chance that variables from the baseline model were causing issues, but that didn’t make a difference.

Getting the posterior predictive on the full data input into the model using the baseline trace and the saved trace.

```
with model2:
post3 = pm.sample_posterior_predictive(idata_bikes, var_names=["mu", "y"], )
with model2:
# pm.set_data({"xdata": xt})
post5 = pm.sample_posterior_predictive(idata4, var_names=["mu", "y"], )
```

This seems to work well enough, with outputs being relatively close to the outputs of the baseline model.

However, when I try to set new data with the new model I an unable too and get a shape error. This seems odd, because setting new data on the baseline model doesn’t throw a shape error, so I am not sure where this error is arising from.

```
with model2:
pm.set_data({"xdata": xt})
post4 = pm.sample_posterior_predictive(idata_bikes, var_names=["mu", "y"])
with model2:
pm.set_data({"xdata": xt})
post6 = pm.sample_posterior_predictive(idata4, var_names=["mu", "y"])
```

error:

```
{
"name": "ValueError",
"message": "size does not match the broadcast shape of the parameters. (10,), (10,), (348,)\nApply node that caused the error: nbinom_rv{0, (0, 0), int64, True}
...
```

So I tried instantiating the model with the new data size

```
with pm.Model() as model3:
xdata2 = pm.MutableData("xdata", xt)
a2 = pm.Exponential("a", 1)
mu_2 = pmb.BART("mu_", xdata2, np.log(yt), m=50)
mu2 = pm.Deterministic("mu", pm.math.exp(mu_2))
y2 = pm.NegativeBinomial("y", mu=mu2, alpha=a2, observed=yt, shape=xdata2.shape[0])
```

And this runs

```
with model3:
# pm.set_data({"xdata": xt})
post6 = pm.sample_posterior_predictive(idata4, var_names=["mu", "y"], )
with model3:
# pm.set_data({"xdata": xt})
post4 = pm.sample_posterior_predictive(idata_bikes, var_names=["mu", "y"], )
```

However the output predictions are not relatively close to what I expect. In fact the output of the BART RV is the same across all observations, so it doesn’t appear that the BART tree structure from the prior training is being used at all.

Finally I tried to pickle the whole model. The model with save and load, but when I try to do anything with the model I receive an error that I believe is associated with the multiprocessing in training the BART model.

NOTE: it says file not found error, but the file will load, it is only one I try to do something with it that it starts having issues.

```
"name": "FileNotFoundError",
"message": "[Errno 2] No such file or directory\nApply node that caused the error: BART_rv{1, (2, 1, 0, 0, 0, 1), floatX, True}(RandomGeneratorSharedVariable(<Generator(PCG64) at 0x7FF34E558900>), [], 11, xdata, [2.7725887 ... .49650756], 20, 0.95, 2.0, [])\nToposort index: 1\nInputs types: [RandomGeneratorType, TensorType(int64, shape=(0,)), TensorType(int64, shape=()), TensorType(float64, shape=(None, None)), TensorType(float64, shape=(348,)), TensorType(int8, shape=()), TensorType(float64, shape=()), TensorType(float32, shape=()), TensorType(float64, shape=(0,))]\nInputs shapes: ['No shapes', (0,), (), (10, 4), (348,), (), (), (), (0,)]\nInputs strides: ['No strides', (8,), (), (8, 80), (8,), (), (), (), (8,)]\nInputs values:
```

If anyone has had success in saving and reloading a model that has a BART RV and wouldn’t mind sharing how they did it, that would be amazing.

Also of note I have been able to successfully save and load with other models that don’t include the BART RV, so I am not convinced it is a OS problem.

Thanks!