Skill: Port MATLAB Algorithm to Python

Use this skill when converting a MATLAB biomechanics script to a vailá module.

Translation Reference

MATLAB	Python (NumPy/SciPy)
`size(A)`	`A.shape`
`zeros(m,n)`	`np.zeros((m, n))`
`ones(m,n)`	`np.ones((m, n))`
`A(:,1)`	`A[:, 0]` (0-indexed!)
`A(end,:)`	`A[-1, :]`
`A'` (transpose)	`A.T`
`A * B` (element-wise)	`A * B`
`A * B` (matrix mult)	`A @ B`
`inv(A)`	`np.linalg.inv(A)`
`norm(v)`	`np.linalg.norm(v)`
`cross(a,b)`	`np.cross(a, b)`
`dot(a,b)`	`np.dot(a, b)`
`linspace(a,b,n)`	`np.linspace(a, b, n)`
`cumtrapz(y,x)`	`scipy.integrate.cumulative_trapezoid(y, x)`
`filtfilt(b,a,x)`	`scipy.signal.filtfilt(b, a, x)`
`butter(n,Wn)`	`scipy.signal.butter(n, Wn)`
`interp1(x,y,xi)`	`np.interp(xi, x, y)`
`fft(x)`	`np.fft.fft(x)`
`mean(A,2)`	`np.mean(A, axis=1)`
`std(A,0,2)`	`np.std(A, axis=1, ddof=0)`
`find(x>0)`	`np.where(x > 0)[0]`
`isnan(x)`	`np.isnan(x)`

MATLAB is 1-indexed. Python is 0-indexed.

% MATLAB
x(1)   → first element
x(end) → last element
A(1,2) → row 1, col 2

# Python
x[0]    # first element
x[-1]   # last element
A[0, 1] # row 0, col 1

% MATLAB
[b,a] = butter(4, fc/(fs/2), 'low');
x_filt = filtfilt(b, a, x);

# Python
from scipy.signal import butter, filtfilt
b, a = butter(4, fc / (fs / 2), btype='low')
x_filt = filtfilt(b, a, x)

Read the MATLAB code and identify:
- Input data format and expected columns
- Key algorithm steps
- Output variables and units
Translate line by line using the table above
Pay special attention to:
- Index offsets (1→0)
- Column-major vs row-major arrays (MATLAB is column-major)
- size(A,1) = rows = A.shape[0]
- size(A,2) = cols = A.shape[1]
Validate output against MATLAB with the same sample data
Wrap in the standard vailá module pattern (see create-analysis-module skill)