Plot graph with 2 variables in matlab - matlab

Question

I'm planning to plot a graph of velocity against time using matlab. The change of time is 0.05 and total time 15. When time change, the graph will change and save a figure of that. I had mat file which contained all the data for time and velocity.
E.g, t=0, v=0, plot and save, t=0.05, v=1, plot and save until t=15.
I tried to use v=v+1 (which acts like i++) but failed to read the value of v in 2nd row. Any other method to do so?
Thank You.
The code is
i = 001
dt = t(2,1) - t(1,1);
k = dt*(i-1);
filename1 = 'front_data';
matFileName = sprintf('%s.mat', filename1);
matData = load(matFileName);
t = matData.time;
fv = matData.front_velocity;
fig = figure%('visible', 'off');
s = t(1,1);
fv = fv(1,1);
lot (s,fv,'*')
pic_filename = sprintf('front_data%02d.jpeg', k);
print(fig,pic_filename,'-djpeg')
istart = 002
iend = 301
for i = istart:iend
k = dt*(i-1);
t = t+dt
filename1 = 'front_data';
matFileName = sprintf('%s.mat', filename1);
matData = load(matFileName);
t = matData.time;
fv = matData.front_velocity;
v = fv(1,1);
v = v+1;
h = figure
axis([0 15 0 0.6])
plot(t,v,'*')
pic_filename = sprintf('front_data%02d.jpeg', k);
print(h,pic_filename,'-djpeg')
end
And the example I refer is the [https://www.mathworks.com/matlabcentral/answers/110632-how-to-increment-a-variable]

Answer 1

I reduced your example to the essential parts.
istart = 2;
iend = 301;
counter=istart;
%load data
% filename1 = 'front_data';
% matFileName = sprintf('%s.mat', filename1);
% matData = load(matFileName);
% t = matData.time;
% fv = matData.front_velocity;
%for demonstaration
t=0:.05:15;
fv=rand(size(t));
for i = istart:iend
%update
time = t(istart:counter);
values = fv(istart:counter);
%plot
plot(time,values,'*')
%increase index
counter=counter+1;
end
As you are loading always the same data in the loop you can do it once outside the loop, and for plotting you just update the length of your vector to be plotted. You could also just append the new value to the actual list.