figure
hold on

alpha = 0.3;

x = 0:0.01:(2*pi);
y = sin(x) + alpha*x;

h = plot(x, y, 'k');
set(h,'linewidth',2.5); % <- Set linewidth here
h = line([x(1), x(end)], [y(1), y(end)]);
set(h,'linewidth',2.5); % <- Set linewidth here

L = 2;
% First line
a = pi/2;
x1 = (a-L/2):0.01:(a+L/2);
b1 = sin(a) + alpha*a;
y1 = (cos(a) + alpha)*(x1-a) + b1;
h = plot(x1, y1, 'm');
set(h,'linewidth',2.5); % <- Set linewidth here

% Second line
a = 3*pi/2;
x1 = (a-L/2):0.01:(a+L/2);
b1 = sin(a) + alpha*a;
y1 = (cos(a) + alpha)*(x1-a) + b1;
h = plot(x1, y1, 'c');
set(h,'linewidth',2.5); % <- Set linewidth here

axis equal
axis off
% MATLAB does not have built-in SVG support. Use the following package to
% convert FIG files to SVG

plot2svg