
<Callout type="warning" heading="🚨 Bug Fix">
  My original check in code block 21 (line 7)...

```python
sumCheck = np.sum(Kp[p,:])
```

...did not capture the case where opposite sign contributions effectively cancel each other out and are missed by the check, leading to the unintended removal of additional rows and columns from the stiffness matrix!

Instead, you should sum across the absolute values from the row, so replace the line above with the following...

```python
sumCheck = np.sum(abs(Kp[p,:]))
```

This results in a check that is actually in line with what I intended!

You can read the discussion that lead to identifying this bug in the comments of [lecture 71](/course/finite-element-analysis-of-3d-structures-using-python/self-weight-part-1-beam-elements)

</Callout>


Please log in or enroll to continue