Hi, I am using PYMC3 to apply a MCMC for the :

ratio = (cos(a) * cos(b) / 0.34202014) **(k-1), iterating over k.

I made two functions one to have the function “ratio_attenuation_model” and another to run the MCMC, These are the functions:

```
def ratio_attenuation_model(data, k):
obsang = data['ObsSatRange'].to_numpy()
incang = data['SunIncAng'].to_numpy()
mag = data['NewScaleMag_2_197'].to_numpy()
# Convert angles to radians
obsang = np.radians(obsang)
incang = np.radians(incang)
# Calculate ratio using the correct equation
ratio = (np.cos(obsang) * np.cos(incang)) / 0.34202014
# Reshape ratio for element-wise operation
# ratio = ratio.flatten()
# Raise the ratio to the power of k-1
ratio_pow = ratio ** (k - 1)
# Add to original magnitude and convert to NumPy array
modeled_mag = mag.values + ratio_pow.values
return modeled_mag
```

```
def ratio_attenu_mcmc(data):
mag_data = data['NewScaleMag_2_197']
with pm.Model() as model:
# Prior distribution for k
# k = pm.Uniform('k', lower=0., upper=1.)
k = pm.Normal('k', mu=0, sd=2)
# Likelihood function
mu_test = ratio_attenuation_model(data, k)
likelihood = pm.Normal('likelihood', mu=mu_test, sd=1, observed=mag_data)
# Step method
step = pm.step_methods.DEMetropolisZ()
# Sample from posterior distribution
trace = pm.sample(draws=1000, step=step)
# Summary statistics
summary = pm.summary(trace)
# Extract trace of k
k_trace = trace['k']
k_df = pd.DataFrame(k_trace, columns=['k'])
return k_df, summary
```

The code is generating this error the following error:

```
ValueError Traceback (most recent call last)
Input In [178], in <cell line: 1>()
----> 1 ratio_attenu_mcmc(ea01)
Input In [177], in ratio_attenu_mcmc(data)
7 k = pm.Normal('k', mu=0, sd=10)
9 # Likelihood function
---> 10 mu_test = ratio_attenuation_model(data, k)
11 likelihood = pm.Normal('likelihood', mu=mu_test, sd=1, observed=mag_data)
13 # Step method
Input In [175], in ratio_attenuation_model(data, k)
7 ratio = (np.cos(data['SunIncAng']) * np.cos(data['ObsSatRange'])) / 0.34202014
9 # Reshape ratio for element-wise operation
10 # ratio = ratio.flatten()
11
12 # Raise the ratio to the power of k-1
---> 13 ratio_pow = ratio ** (k - 1)
15 # Add to original magnitude and convert to NumPy array
16 modeled_mag = data['NewScaleMag_2_197'].values + ratio_pow
File ~/.local/lib/python3.10/site-packages/pandas/core/ops/common.py:72, in _unpack_zerodim_and_defer.<locals>.new_method(self, other)
68 return NotImplemented
70 other = item_from_zerodim(other)
...
4888 except (ValueError, NotScalarConstantError):
4889 raise ValueError(f"Length of {v} cannot be determined")
-> 4891 raise ValueError(f"Length of {v} cannot be determined")
ValueError: Length of Elemwise{pow,no_inplace}.0 cannot be determined
```

From what I read in some comments, this error can be generated because the variables of the function “ratio” must be numpy arrays. I have been careful to do so but I still get the same error. Do you have any other ideas as to why the error is being generated, please let me know.

pymc3 v.3.11.5

Theano-PyMC v.1.1.2

pymc3 v.3.11.5