# sympy__sympy-12454

> Based on the issue description, I can understand the problem clearly and provide a fix. The issue is in sympy/matrices/matrices.py in the is_upper method. 

- Source: https://doutorai.pt/en/components/skills__sympy-sympy-12454
- Type: Skills
- Category: AI research
- Downloads: 0
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An open-source community component, curated and adapted by Doutor AI.

## What it does and how to use it

A **skill** that teaches Claude Code to do ai research tasks well. It is packaged knowledge the model uses whenever it is relevant.

1. Install the skill (command above).
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## Install (Claude Code)

```bash
mkdir -p .claude/skills/sympy-sympy-12454 && curl -fsSL https://doutorai.pt/data/lib/skills__sympy-sympy-12454.md -o .claude/skills/sympy-sympy-12454/SKILL.md
```

Paste this command into the terminal, in your project folder, and the component installs automatically.

## Content

````
Based on the issue description, I can understand the problem clearly and provide a fix. The issue is in `sympy/matrices/matrices.py` in the `is_upper` method. The code iterates over indices that go beyond the matrix dimensions for tall matrices (more rows than columns).

The current code:
```python
return all(self[i, j].is_zero
           for i in range(1, self.rows)
           for j in range(i))
```

For a 4x2 matrix, this generates indices including (3, 2) which is out of bounds since the matrix only has 2 columns (indices 0 and 1).

The fix should limit `j` to be less than both `i` and `sel

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````

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