how to create a vector

Question

Abdullah Jizani 2016-5-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284470-how-to-create-a-vector

编辑： Abdullah Jizani 2016-5-26

Hello everyone, I hope you are doing well. I need some help with my matlab project. I''m finding the velocity and time after each 1 meter displacement. It''s good when I''m doing that and I''m actually getting correct results. However, I couldn''t find the velocity and time after for example 1.5 or 1.6 meter. this is my program, so can you please help me with it.

function [v,t]=freefall(h)  
g=9.81;
%Gravity in m^2/s 
for k=1:h
    v(k)=sqrt(2*g*k);
end 
for
k=1:h
    t(k)=sqrt(2*k/g);
end 
plot(t,v)
xlabel(''Time
(s)'')
ylabel(''Velocity (m/s)'')
title(''Free fall: velocity vs time'')

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Answer 1

Star Strider 2016-5-16

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284470-how-to-create-a-vector#answer_222330

在 MATLAB Online 中打开

Use the interp1 function.

If I understand your code correctly, this will work. Add these lines to the end of your code:

k = 1:h;                                                    % Displacement
dspl_intrp = [1.5; 1.6];                                    % Displacements To Interpolate
vt_intrp = interp1(k, [v' t'], [1.5; 1.6], 'linear');       % Interpolate Velocity & Time
fprintf(1, 'Displacement %.2f,  Velocity = %.2f,  Time = %.2f\n',  [dspl_intrp vt_intrp]')
Displacement 1.50,  Velocity = 5.35,  Time = 0.55
Displacement 1.60,  Velocity = 5.53,  Time = 0.56

I added the fprintf call to show that the result appears to be correct.

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Abdullah Jizani 2016-5-16

but it shows me this error ??? Attempted to access v(1.1); index must be a positive integer or logical.

Error in ==> freefall at 7 v(k)=sqrt(2*g*k);

Star Strider 2016-5-16

在 MATLAB Online 中打开

I forgot that you used it as an index.

This works:

g=9.81; %Gravity in m^2/s 
d = 1 : 0.1 : h;                                    % Displacement Vector
for k=1:length(d)
    v(k)=sqrt(2*g*d(k));
end 
for k=1:length(d)
    t(k)=sqrt(2*d(k)/g);
end 
plot(t,v)
xlabel('Time (s)')
ylabel('Velocity (m/s)')
title('Free fall: velocity vs time')

Note that here you have to change the ‘k’ reference as the independent variable in your calculations to ‘d(k)’. This also gives you flexibility to make ‘d’ anything you want, even negative or zero, because ‘k’ is now derived from it.

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