converting python code to matlab and getting it plotted

I been trying to get this python code to work in matlab. Besides converting issues I probably have a lot of other mistakes in it as I am just a beginner.

% constants
L = 100;    % length of bar in km
dx = 1;    % spatial grid spacing km
beta = 4;   % shear wave velocity in km/s
dt = 0.1;   % time spacing in seconds
T = 5;        % total time in sec
N = int(T/dt); % number of time steps
tmax = 30; % wave run time sec

t = [0:dt:tmax]; %time vec
nt = length (t);

% Define initial conditions
u = zeros(int(L/dx)+1); % displacement array
u(int(50e3/dx)) = 1;       % source at u(50 km)

% intialize 3 displacement vectors
%u3 = new solution
%u2 = previous solution
%u1 = previous previous solution

% displacement arrays
u1 = zeroes (1, 101);
u2 = u1;
u3 = u1;

% boundary conditions
u(0) = 0;
u(-1) = 0;

% Define finite difference coefficients
A = (beta*dt/dx)^2
B = 2 - 2*A

% Solve wave equation using finite differences
for  n = range(1,N)
    u(1:-1) = B*u(1:-1) - u(1:-1) + A*(u (2: + u :-2))
    u(int(50e3/dx)) = np.sin(2*np.pi*n*dt/5)
end

% Plot solution
figure(1); hold on; grid on; axis equal

xline(0,'-','linewidth',2); yline(0,'-','linewidth',2) %adding x and y line

set(0,'DefaultLineLineWidth',5,'DefaultAxesFontSize',12)

x = linspace(0, L, int(L/dx)+1)
plot(x, u)
xlabel('Distance (m)')
ylabel('Displacement')
show()

% initial condition
u3(50) = sin(pi*tlen/5)^2

% boundary conditions
u3(0) = u3(1)  % stress-free boundary
u3(L) = 0  % fixed boundary

% Define plotting function
figure plot_u(u, t):
    x = arange(0, L+dx, dx)
    plot(x, u)
    title('t = {t:.2f} s')
    xlabel('x (km)')
    ylabel('u (m)')
    ylim(-0.1, 0.1)
    show()

%%% Solve PDE using finite differences
t = 0
if t <= tlen
    t = dt
    for i [1, L]
        rhs = beta^2 * (u2[i+1] - 2*u2[i] + u2[i-1]) / dx^2
        u3[i] = 2*u2[i] - u1[i] + dt^2 * rhs
    % Apply boundary conditions
    u3(0) = u3(1)  % stress-free boundary
    u3(L) = 0  % fixed boundary
    if t <= tlen
        u3(50) = sin(np.pi*t/tlen)^2

    % Update displacement arrays
    u1 = copy(u2)
    u2 = copy(u3)
    
    % Plot every 4 s
    if t % 4 < dt:
        plot_u(u2, t)
    end
    end
    end
end

%% Calculate velocities of pulses
t1 = 1.5  % time to measure velocity of first pulse
t2 = 12.5  % time to measure velocity of second pulse
x1 = 25  % distance to measure velocity of first pulse
x2 = 75  % distance to measure velocity of second pulse
vel1 = (u2(x1+1,t1) - u2(x1-1,t1)) / (2*dx*dt)
vel2 = (u2(x2+1,t2) - u2(x2-1,t2)) / (2*dx*dt)
fprintf('Velocity of first pulse: {vel1:.2f} km/s')
fprintf('Velocity of second pulse: {vel2:.2f} km/s')

figure(2) % displacement at endpoints as a function of time
x_endpoints = [0, L]
u_endpoints = u2*[0,':'], u2*[L,':']
for i % in range(2):
    plot(arange(0, tlen+dt, dt), u_endpoints[i])
    xlabel('t (s)')
    ylabel('f u(x_endpoints[i] km) (m)')
    show()

% Plot displacement at crossing
(initialize t, dx, dt, tlen, beta and u1, u2, u3 arrays) 

while t <= 33
    t = t + dt;
    for i = 2:99
        rhs = beta^2 * (u2(i+1) - 2*u2(i) + u2(i-1)) / dx^2;
        u3(i) = dt^2 * rhs + 2*u2(i) - u1(i);
    end
    u3(1) = u3(2);    % stress-free boundary
    u3(100) = 0;      % fixed boundary
    if t <= tlen
        u3(50) = sin(pi * t/tlen)^2;
    end
    u1 = u2;
    u2 = u3;
    % output u2 at desired times
end

[KSSV]

What you have copied is a complete python code? What exactly is the code about?

[Kathleen]

it was a python code. I tried to adapt it as much as possible. the goal is to get the following graphs.

[Rik]

Have a read here and here. It will greatly improve your chances of getting an answer. What is the actual problem you're having?

Answer 1

[Sarthak]

Hi Kathleen,

As per my understanding, there is no direct way to convert python code to MATLAB.

However you can try the following approaches:

• You have to directly write the code from scratch. You should be able to find direct MATLAB coutnerparts to PYTHON functions.
• You can use the MATLAB API to call python script in MATLAB: https://www.mathworks.com/help/matlab/call-python-libraries.html
• As of MATLAB 8.4(R2014b) you can call Python directly from MATLAB. For more information, please go through the following documentation: https://www.mathworks.com/help/matlab/python-language.html
• Can also leverage the following library on FileExhange: https://www.mathworks.com/matlabcentral/fileexchange/114455-python-for-matlab-development

Please refer to the following MATLAB answers post with similar issue: https://www.mathworks.com/matlabcentral/answers/416129-how-to-convert-python-code-into-matlab

I hope the above solutions successfully resolve your query!