# Issue passing multiple sequences to aesara.scan

**URL:** <https://discourse.pymc.io/t/issue-passing-multiple-sequences-to-aesara-scan/10709>\
**Category:** v5\
**Tags:** aesara\
**Created:** [November 1, 2022, 12:31am UTC](https://discourse.pymc.io/t/issue-passing-multiple-sequences-to-aesara-scan/10709 "2022-11-01T00:31:30Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![davipatti](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/davipatti/32/5146_2.png) [@davipatti](https://discourse.pymc.io/u/davipatti)\
**Post date:** [November 1, 2022, 12:31am UTC](https://discourse.pymc.io/t/issue-passing-multiple-sequences-to-aesara-scan/10709/1 "2022-11-01T00:31:31Z")

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Hello

I’m getting an error when passing multiple sequences to `aesara.scan`:

```python
import aesara
import pymc as pm
import numpy as np

for module in aesara, pm, np:
    print(module. __name__ , module. __version__ )

# Generate some dummy data
m = 42
n = 8
g = np.random.randint(1, 5, (m, n))
y = np.random.uniform(size=(m, n))

with pm.Model():
    p = pm.Beta("p", alpha=1, beta=100)
    i = pm.Bernoulli("i", p, size=(m, n)) * 1.0
    rho = pm.Beta("r", alpha=10, beta=1)
    y0 = aesara.tensor.zeros(m)
    mu, _ = aesara.scan(
        lambda i, g, y, rho: rho**g * y + i,
        sequences=[i.T, g.T],
        outputs_info=y0,
        non_sequences=[rho],
    )
    sigma = pm.Exponential("sigma", 1)
    pm.Normal("y_hat", mu=mu.T, sigma=sigma, observed=y)
    pm.sample()

```

```auto
aesara 2.8.7
pymc 4.3.0
numpy 1.23.4
Traceback (most recent call last):
  File "/Users/pattinson/djpiri/content/Notes/2022-10-31-aesara-bug/main.py", line 21, in <module>
    mu, _ = aesara.scan(
  File "/Users/pattinson/.virtualenvs/pymc-fresh-env/lib/python3.10/site-packages/aesara/scan/basic.py", line 681, in scan
    scan_seqs = [seq[:actual_n_steps] for seq in scan_seqs]
  File "/Users/pattinson/.virtualenvs/pymc-fresh-env/lib/python3.10/site-packages/aesara/scan/basic.py", line 681, in <listcomp>
    scan_seqs = [seq[:actual_n_steps] for seq in scan_seqs]
TypeError: slice indices must be integers or None or have an __index__ method

```

A similar model with only a single sequence (removing `g`) samples fine:

```python

with pm.Model():
    p = pm.Beta("p", alpha=1, beta=100)
    i = pm.Bernoulli("i", p, size=(m, n)) * 1.0
    rho = pm.Beta("r", alpha=10, beta=1)
    y0 = aesara.tensor.zeros(m)
    mu, _ = aesara.scan(
        lambda i, y, rho: rho * y + i,
        sequences=[i.T],
        outputs_info=y0,
        non_sequences=[rho],
    )
    sigma = pm.Exponential("sigma", 1)
    pm.Normal("y_hat", mu=mu.T, sigma=sigma, observed=y)
    pm.sample()

```

Is this a problem with aesara? Or have I misunderstood something?

Thanks a lot  
David

---

<div class="post-metadata">

**Author:** ![jessegrabowski](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/jessegrabowski/32/5010_2.png) [@jessegrabowski](https://discourse.pymc.io/u/jessegrabowski)\
**Post date:** [November 1, 2022, 11:57am UTC](https://discourse.pymc.io/t/issue-passing-multiple-sequences-to-aesara-scan/10709/2 "2022-11-01T11:57:46Z")

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I believe this is because `g` is a numpy array, not an aesara tensor. Use the function `aesara.tensor.as_tensor_variable` to convert it before you pass it into the scan, and things should work.

---

<div class="post-metadata">

**Author:** ![davipatti](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/davipatti/32/5146_2.png) [@davipatti](https://discourse.pymc.io/u/davipatti)\
**Post date:** [November 1, 2022, 3:28pm UTC](https://discourse.pymc.io/t/issue-passing-multiple-sequences-to-aesara-scan/10709/3 "2022-11-01T15:28:34Z")

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That’s it, thanks a lot!