How to solve a MATLAB script that will plot cos(x) for x values ranging from –pi to pi with argument to change line widths?

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I am trying to write a MATLAB function that will plot cos(x) for x values ranging from –pi to pi in steps of 0.1, using black stars (*). It will do this three times across in one Figure Window, with varying line widths.
(Note: Even if individual points are plotted rather than a solid line, the line width property will change the size of these points.) If no arguments are passed to the function, the line widths will be 1, 2, and 3.
Else, an argument is passed to the function, it is a multiplier for these values (e.g., if 3 is passed, the line widths will be 3, 6, and 9). The line widths will be printed in the titles on the plots.
I have started progress by displaying three plots in one figure but I do not know how the syntax works for an else condition when an argument has to be passed for the function call. I always end up with default values for line widths of 1, 2, and 3. Any advice or major change to the approach that you see best will be appreciated.
function plotCos(varargin)
% Default line widths
lw1 = 1;
lw2 = 2;
lw3 = 3;
% If a random number is passed as an argument
% Example: If 3 is passed, the line widths will be 3, 6, and 9
if nargin == 1
% Multiply the default line widths with that number
lw1 = lw1 * varargin{1};
lw2 = lw2 * varargin{1};
lw3 = lw3 * varargin{1};
end
% Create the figure window
f = figure();
% Set the title
f.Name = 'Plot of cos(x) from -pi to pi';
% Set the position of the figure window to be in the center of the screen
f.Position = [100 100 600 400];
% Set the axes
a1 = subplot(1, 3, 1);
a2 = subplot(1, 3, 2);
a3 = subplot(1, 3, 3);
% Set the title of the first plot
a1.Title.String = sprintf('Line width: %d', lw1);
% Set the title of the second plot
a2.Title.String = sprintf('Line width: %d', lw2);
% Set the title of the third plot
a3.Title.String = sprintf('Line width: %d', lw3);
% Set the x and y axes
a1.XAxis.Label.String = 'x';
a1.YAxis.Label.String = 'cos(x)';
a2.XAxis.Label.String = 'x';
a2.YAxis.Label.String = 'cos(x)';
a3.XAxis.Label.String = 'x';
a3.YAxis.Label.String = 'cos(x)';
% Set the x and y limits
a1.XLim = [-pi, pi];
a1.YLim = [-1, 1];
a2.XLim = [-pi, pi];
a2.YLim = [-1, 1];
a3.XLim = [-pi, pi];
a3.YLim = [-1, 1];
% Create an array of values from -pi to pi, in steps of 0.1
vals = -pi:0.1:pi;
% Plot the cos(x) values with line width lw1
plot(a1, vals, cos(vals), 'k*', 'LineWidth', lw1);
% Plot the cos(x) values with line width lw2
plot(a2, vals, cos(vals), 'k*', 'LineWidth', lw2);
% Plot the cos(x) values with line width lw3
plot(a3, vals, cos(vals), 'k*', 'LineWidth', lw3);
% Set the x and y ticks
a1.XTick = -pi:pi/2:pi;
a1.YTick = -1:1;
a2.XTick = -pi:pi/2:pi;
a2.YTick = -1:1;
a3.XTick = -pi:pi/2:pi;
a3.YTick = -1:1;
% Set the x and y grid lines
a1.XGrid = 'on';
a1.YGrid = 'on';
a2.XGrid = 'on';
a2.YGrid = 'on';
a3.XGrid = 'on';
a3.YGrid = 'on';
% Display the line widths in the titles
a1.Title.String = sprintf('Line width: %d', lw1);
a2.Title.String = sprintf('Line width: %d', lw2);
a3.Title.String = sprintf('Line width: %d', lw3);
% Set the figure to be visible
f.Visible = 'on';
% Display the plot
drawnow
% Save the plot as a png image in the current folder
saveas(f, 'plotCos.png');
end
Rik on 18 Jun 2022
How do you call this function? I can't see anything fundamentally wrong.

Abolfazl Chaman Motlagh on 18 Jun 2022
there is nothing wrong with the code or anything. all you should do is calling the function. you can either save the function in .m file and call it from another script (or in command window)(the name of file should be same as function). or define function after the main script(use different name for file). the below code is exactly yours except the fancy parts and comments :)
plotCosfunc
plotCosfunc(4)
function plotCosfunc(varargin)
lw1 = 1;
lw2 = 2;
lw3 = 3;
if nargin == 1
lw1 = lw1 * varargin{1};
lw2 = lw2 * varargin{1};
lw3 = lw3 * varargin{1};
end
f = figure();
f.Name = 'Plot of cos(x) from -pi to pi';
a1 = subplot(1, 3, 1);
a2 = subplot(1, 3, 2);
a3 = subplot(1, 3, 3);
vals = -pi:0.1:pi;
plot(a1, vals, cos(vals), 'k*', 'LineWidth', lw1);
plot(a2, vals, cos(vals), 'k*', 'LineWidth', lw2);
plot(a3, vals, cos(vals), 'k*', 'LineWidth', lw3);
grid(a1,'on')
grid(a2,'on')
grid(a3,'on')
a1.Title.String = sprintf('Line width: %d', lw1);
a2.Title.String = sprintf('Line width: %d', lw2);
a3.Title.String = sprintf('Line width: %d', lw3);
end

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