Matlab question for cantilever beam

My homework assignment involves graphing the deflection equation of a beam. I am fairly new to matlab and i am coming across an error in how i am writing the codes since i am not using matrices

Here is my code and i get this error when ran

??? Subscript indices must either be real positive integers or logicals.

Error in ==> inertia at 38
U(x)= F./E.*I.*(x.^3-3.*L.*x.^2);

E = input('Youngs Modulus:');
r = input('Enter 1 for circular cross section, Enter 2 for rectangular cross section') ;
if(r==1)
    d = input('Dimater:');
    I = (pi*(d/2)^4)/4;   
elseif(r==2)
    b = input('Width of Beam:');
    h = input('Height of Beam:');
    I = (b*h^3)/12;
end
%Above runs how to find the I of cross section this will be used for figure
%1 and 2
%now need to create code to input the length of beam and where loads can be
%like element stiffness matrix

L = input('Length of beam:');
F = input('Force');
j = input('Enter 1 if force is at end of beam, Enter 2 if force is in middle of beam') ;
if (j==1)
    w = F*L^2/3*E*I ; %this give max deflection 
elseif (j==2)
    a = input('Location from support of point');
    w = F*a^2/6*E*I*(a-3*l);
end

%above found the max deflection for the two different cases, now code needs
%to be written so i can graphically show these inputs i also need to add in
%how to see the values

%here right formula for graph and take values from above to plot it 
%using equation for elastic curve

str=['deflection: ', num2str(w)];
disp(str)

x= 0:0.1:L;

U(x)= F./E.*I.*(x.^3-3.*L.*x.^2);
y = 0:U(x):w;

plot(x,y)

Answer 1

[Walter Roberson]

Change your line

U(x)= F./E.*I.*(x.^3-3.*L.*x.^2);

to

U = F./E.*I.*(x.^3-3.*L.*x.^2);

However, I do not know what U represents to you (you have not comment about it), so I cannot figure out how to correct your 0:U(x):w expression for y. My speculation is that you want

y = U;

but I do not know.

Answer 2

[Sven]

Hi Caroline,

The problem is here:

x= 0:0.1:L;
U(x)= F./E.*I.*(x.^3-3.*L.*x.^2);

I think you simply mean:

x= 0:0.1:L;
U= F./E.*I.*(x.^3-3.*L.*x.^2);

You'll note (if you run your code one line at a time) after the first line that x is an array starting at 0 and with lots of elements up to the value of L. It makes no sense for the xth element of U to be accessed in this context.

And when you plot, I think you're just trying to do this:

plot(x,U)

... I'm not quite sure what your assignment to y actually means.

Did this help you out?

Answer 3

[Caroline]

Thank you, I just was not parametizing correctly for my two values that fix helped it

[Abhishek Pawarq]

Hey man can you please post the corrected code