Plotting animation results in blank graph - matlab

Question

I have written this code and it will not plot. I run it with a 0:.5:100 and get a blank graph in Matlab. As well this is a inclined plane friction problem. I need to create an animation in Matlab that shows the blocks sliding based on inputs.
%Numerical Project Code 1
%mass ratio input
mratio = input('Enter the Mass Ratio(m/M): ');
%angle input
theta = input('Enter Angle in Degrees Between 0 and 90: ');
%static coeff input
mus = input('Enter Coefficient of Static Friction: ');
%kinetic coeff input
muk = input('Enter Coefficient of Kinetic Friction: ');
%constants
g = 9.81;
%interface formating
disp('--------------------------------------------');
disp('All Friction Forces are given in terms of the mass on the slope (M)');
%Loops
%NETUP
if mratio > sind(theta)
%static only
if mratio <= (sind(theta) + (mus*cosd(theta)))
ff = g*(mratio - sind(theta));
fprintf("Friction Force = %f M Newtons\n",ff);
fprintf("The Direction of the Friction Force is down the slope and the block not moving.\n")
%kinetic only
else
ff = muk * g * cosd(theta);
fprintf("Friction Force = %f M Newtons\n",ff);
fprintf("The Direction of the Friction Force is down the slope and the block is sliding up the slope.\n");
end
%NETDOWN
elseif mratio < sind(theta)
%static only
if sind(theta) <= (mratio + (mus*cosd(theta)))
ff = g*(sind(theta) - mratio);
fprintf("Friciton Force = %f M Newtons\n",ff);
fprintf("The Direction of the Friction Force is up the slope and the block is not moving.\n")
%kinetic only
else
ff = muk * g * cosd(theta);
fprintf("Friction Force = %f M Newtons\n",ff);
fprintf("The Direction of the Friction Force is up the slope and the block is sliding down the slope.\n");
end
%NETZERO
else
fprintf("Friction Force = 0 Newtons\n");
end
%graph
for i = 0:0.01:1
mratiog = i;
if mratiog > sind(theta)
if mratiog <= (sind(theta) + (mus*cosd(theta)))
ffg = g*(mratiog - sind(theta));
else
ffg = muk * g * cosd(theta);
end
elseif mratiog < sind(theta)
if sind(theta) <= (mratiog + (mus*cosd(theta)))
ffg = g*(sind(theta) - mratiog);
else
ffg = muk * g * cosd(theta);
end
else
ffg = 0;
end
plot (ffg,mratio, 'r:')
end

Answer 1

In addition to Erik's comments I see two other issues:
the plot changes its axis with each new iteration, so you can not see
the animation properly. It would work better if you calculate all
your points before plotting them. Then you can use min and max of data
dimensions to set axis limits. If you don't use 'hold on' you need to set the limits in each iteration.
you need to use 'pause' to slow down the
animation. otherwise you see only the last data point.
Here is a working example of the 'graph' part:
%graph
i_arr = 0:0.01:1;
n = numel(i_arr);
ffg_mratio_arr = zeros(n, 2);
for i = 1:n
mratiog = i_arr(i);
if mratiog > sind(theta)
if mratiog <= (sind(theta) + (mus*cosd(theta)))
ffg = g*(mratiog - sind(theta));
else
ffg = muk * g * cosd(theta);
end
elseif mratiog < sind(theta)
if sind(theta) <= (mratiog + (mus*cosd(theta)))
ffg = g*(sind(theta) - mratiog);
else
ffg = muk * g * cosd(theta);
end
else
ffg = 0;
end
ffg_mratio_arr(i,:) = [ffg mratio];
end
% calculating the axis limits
x_min = min(ffg_mratio_arr(:, 1))-1;
x_max = max(ffg_mratio_arr(:, 1))+1;
y_min = min(ffg_mratio_arr(:, 2))-1;
y_max = max(ffg_mratio_arr(:, 2))+1;
% animation
figure;
for i = 1:n
plot (ffg_mratio_arr(i,1), ffg_mratio_arr(i,2), 'ro');
xlim([x_min x_max]);
ylim([y_min y_max]);
pause(0.01);
end