Cannot plot iterations.

I'm trying to plot iterations but it doesn't seem to be working. The figure pops up but no points do. This is confusing because both variables i'm plotting have the same size. How to I plot the iterations of v(k-1) against x ?

x=20:30;%range of inital velocities plotted 
figure;
hold on
for i=20:30       %to iterate through a few intial velocities.
    v0=i;
    v(1)=v0;
    s(1)=0;
    
for k=2:length(t)  %This loop uses eulers formula to calculate velocity and displacment
    muk=0.7;
    a=-muk*g;
    dvdt=a;         %acceleration
    dsdt = v(k-1);  %velocity = displacment over time
    
    %approx value of v at current step given previous value
    v(k) = v(k-1) + dvdt*dt;
    
    %approx value of s at current step given previous value
    s(k)=s(k-1)+dsdt*dt; 
    
    %Break loop when velocity starts to become negative 
    if v(k) < 0 
        break
    end
end

%Value before the first negative velocity value (this is the time where 
%the car has stopped). 
v(k-1)       %this iterates through initial velocities corresponding to the final positive velocity value in each case

%plotting
plot(x,v(k-1))   
end

[Sriram Tadavarty]

what are the values of t, dt, and g? what are you trying to plot? The command plot(x,v(k-1)) will plot only the last element of v.. Try plot(x(1:length(v)),v)

Answer 1

[KSSV]

clear all ; clc; 
t=20:30;%range of inital velocities plotted 
dt = min(diff(t)) ; 
g = 9.81 ; 
figure;
hold on
for i=20:30       %to iterate through a few intial velocities.
    v0=i;
    v(1)=v0;
    s(1)=0;
    
for k=2:length(t)  %This loop uses eulers formula to calculate velocity and displacment
    muk=0.7;
    a=-muk*g;
    dvdt=a;         %acceleration
    dsdt = v(k-1);  %velocity = displacment over time
    
    %approx value of v at current step given previous value
    v(k) = v(k-1) + dvdt*dt;
    
    %approx value of s at current step given previous value
    s(k)=s(k-1)+dsdt*dt; 
    
    %Break loop when velocity starts to become negative 
    if v(k) < 0 
        break
    end
end

%Value before the first negative velocity value (this is the time where 
%the car has stopped). 
v(k-1)       %this iterates through initial velocities corresponding to the final positive velocity value in each case

%plotting
plot(t,v(k-1),'*')   
end

[Matthew Worker]

This still does not work unfortunately.

[KSSV]

It is able to plot right?

[Matthew Worker]

The function runs with no errors, but no plot shows. Just an empty figure screen.

[KSSV]

It is plotting...I have attched the image...Edited the code..check now.

[Matthew Worker]

I replaced plot(x,v(k-1)) from my code with plot(x,v(k-1), '*') and it worked! I'm not sure why but it wont work if i use '--r' or don't specify a format.

Do you know what might be going on?

[KSSV]

It is because your v(k-1) is only a single number i.e scalar. Which you can only plot by using markers.

[Matthew Worker]

Thank you so much !