Run MATLAB-Style Octave Code from Python with oct2py — Colab Guide

!apt-get -qq update
!apt-get -qq install -y octave gnuplot octave-signal octave-control > /dev/null
!python -m pip -q install oct2py scipy matplotlib pillow

from oct2py import Oct2Py, Oct2PyError
import numpy as np, matplotlib.pyplot as plt, textwrap
from scipy.io import savemat, loadmat
from PIL import Image


oc = Oct2Py()
print("Octave version:", oc.eval("version"))


def show_png(path, title=None):
   img = Image.open(path)
   plt.figure(figsize=(5,4)); plt.imshow(img); plt.axis("off")
   if title: plt.title(title)
   plt.show()

print("\n--- Basic eval ---")
print(oc.eval("A = magic(4); A"))
print("eig(A) diag:", oc.eval("[V,D]=eig(A); diag(D)'") )
print("sin(pi/4):", oc.eval("sin(pi/4)"))


print("\n--- NumPy exchange ---")
x = np.linspace(0, 2*np.pi, 100)
y = np.sin(x) + 0.1*np.random.randn(x.size)
y_filt = oc.feval("conv", y, np.ones(5)/5.0, "same") 
print("y_filt shape:", np.asarray(y_filt).shape)


print("\n--- Cells & Structs ---")
cells = ["hello", 42, [1,2,3]]
oc.push("C", cells)
oc.eval("s = struct('name','Ada','score',99,'tags',{C});")
s = oc.pull("s")
print("Struct from Octave -> Python:", s)

gd_code = r"""
function [w, hist] = gradient_descent(X, y, alpha, iters)
 % X: (n,m), y: (n,1). Adds bias; returns weights and loss history.
 if size(X,2) == 0, error('X must be 2D'); end
 n = rows(X);
 Xb = [ones(n,1), X];
 m = columns(Xb);
 w = zeros(m,1);
 hist = zeros(iters,1);
 for t=1:iters
   yhat = Xb*w;
   g = (Xb'*(yhat - y))/n;
   w = w - alpha * g;
   hist(t) = (sum((yhat - y).^2)/(2*n));
 endfor
endfunction
"""
with open("gradient_descent.m","w") as f: f.write(textwrap.dedent(gd_code))


np.random.seed(0)
X = np.random.randn(200, 3)
true_w = np.array([2.0, -1.0, 0.5, 3.0])    
y = true_w[0] + X @ true_w[1:] + 0.3*np.random.randn(200)
w_est, hist = oc.gradient_descent(X, y.reshape(-1,1), 0.1, 100, nout=2)
print("Estimated w:", np.ravel(w_est))
print("Final loss:", float(np.ravel(hist)[-1]))

print("\n--- Octave plotting -> PNG -> Python display ---")
oc.eval("x = linspace(0,2*pi,400); y = sin(2*x) .* exp(-0.2*x);")
oc.eval("figure('visible','off'); plot(x,y,'linewidth',2); grid on; title('Damped Sine (Octave)');")
plot_path = "/content/oct_plot.png"
oc.eval(f"print('{plot_path}','-dpng'); close all;")
show_png(plot_path, title="Octave-generated Plot")

print("\n--- Packages (signal/control) ---")
signal_ok = True
try:
   oc.eval("pkg load signal; pkg load control;")
   print("Loaded: signal, control")
except Oct2PyError as e:
   signal_ok = False
   print("Could not load signal/control, skipping package demo.\nReason:", str(e).splitlines()[0])


if signal_ok:
   oc.push("t", np.linspace(0,1,800))
   oc.eval("x = sin(2*pi*5*t) + 0.5*sin(2*pi*40*t);")
   oc.eval("[b,a] = butter(4, 10/(800/2)); xf = filtfilt(b,a,x);")
   xf = oc.pull("xf")
   plt.figure(); plt.plot(xf); plt.title("Octave signal package: filtered"); plt.show()

print("\n--- Function handles ---")
oc.eval("""
f = @(z) z.^2 + 3*z + 2;
vals = feval(f, [0 1 2 3]);
""")
vals = oc.pull("vals")
print("f([0,1,2,3]) =", np.ravel(vals))


quadfun_code = r"""
function y = quadfun(z)
 y = z.^2 + 3*z + 2;
end
"""
with open("quadfun.m","w") as f: f.write(textwrap.dedent(quadfun_code))
vals2 = oc.quadfun(np.array([0,1,2,3], dtype=float))
print("quadfun([0,1,2,3]) =", np.ravel(vals2))

print("\n--- .mat I/O ---")
data_py = {"A": np.arange(9).reshape(3,3), "label": "demo"}
savemat("demo.mat", data_py)
oc.eval("load('demo.mat'); A2 = A + 1;")
oc.eval("save('-mat','demo_from_octave.mat','A2','label');")
back = loadmat("demo_from_octave.mat")
print("Keys from Octave-saved mat:", list(back.keys()))


print("\n--- Error handling ---")
try:
   oc.eval("no_such_function(1,2,3);")
except Oct2PyError as e:
   print("Caught Octave error as Python exception:\n", str(e).splitlines()[0])

print("\n--- Simple Octave benchmark ---")
oc.eval("N = 2e6; a = rand(N,1);")


oc.eval("tic; s1 = sum(a); tv = toc;")
t_vec = float(oc.pull("tv"))


oc.eval("tic; s2 = 0; for i=1:length(a), s2 += a(i); end; tl = toc;")
t_loop = float(oc.pull("tl"))


print(f"Vectorized sum: {t_vec:.4f}s | Loop sum: {t_loop:.4f}s")


print("\n--- Multi-file pipeline ---")
pipeline_m = r"""
function out = mini_pipeline(x, fs)
 try, pkg load signal; catch, end
 [b,a] = butter(6, 0.2);
 y = filtfilt(b,a,x);
 y_env = abs(hilbert(y));
 out = struct('rms', sqrt(mean(y.^2)), 'peak', max(abs(y)), 'env', y_env(1:10));
end
"""
with open("mini_pipeline.m","w") as f: f.write(textwrap.dedent(pipeline_m))


fs = 200.0
sig = np.sin(2*np.pi*3*np.linspace(0,3,int(3*fs))) + 0.1*np.random.randn(int(3*fs))
out = oc.mini_pipeline(sig, fs, nout=1)
print("mini_pipeline -> keys:", list(out.keys()))
print("RMS ~", float(out["rms"]), "| Peak ~", float(out["peak"]), "| env head:", np.ravel(out["env"])[:5])


print("\nAll sections executed. You are now running MATLAB/Octave code from Python!")