Cannot plot iterations.

Question

Matthew Worker 2020-3-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/511252-cannot-plot-iterations

评论： Matthew Worker 2020-3-17

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

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Sriram Tadavarty 2020-3-17

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)

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Answer 1

KSSV 2020-3-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/511252-cannot-plot-iterations#answer_420473

编辑：KSSV 2020-3-17

在 MATLAB Online 中打开

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