To complement @FrédéricC 's answer, here is how to find that the relevant source file is indeed `src/sage/matrix/matrix2.pyx`

: in a SageMath session, run

```
sage: m = matrix(1)
sage: m.jordan_form?
```

At the end of the returned documentation, you can see `src/sage/matrix/matrix2.pyx`

in the `File:`

field.
Then you can browse the github directory to that file, as indicated by @FrédéricC.

Alternatively, you can run `git blame`

on your computer: first open a terminal and go to the subdirectory `src/sage/matrix`

of your SageMath root directory (the latter is returned by `sage: !echo $SAGE_ROOT`

in a SageMath terminal). Then determine the line at which the definition of the method `jordan_form`

starts by running

```
grep -n "def jordan_form" matrix2.pyx
```

For SageMath 9.7, the output should be:

```
10823: def jordan_form(self, base_ring=None, sparse=False, subdivide=True, transformation=False, eigenvalues=None, check_input=True):
```

Hence the line number is 10823 and you may run

```
git blame -L 10823 matrix2.pyx
```

to see the list of contributors to the method `jordan_form`

.