Vectors must be the same length with plot of Shear Force Diagram

I'm not famililar with the error. If I run the plot for the moment diagram it works, but not for the shear force.

%% conversions
w = 4;       % VDL in k/ft
d = 12;      % Distance for VDL
P1 = w*d;    % VDL to Point Load in kip
a = 6;       % centroid of the point load
P2 = 60;

%% Reaction Forces
Ay = P1 + P2;
MA = P1*a + P2*20;

%% Consider the left of a section through a-a
x1 = linspace(0,12);
P3 = P1*x1;

% Equilibrium
Va = Ay - P3;
Ma = (Ay*x1)-(P3.*(x1/2))-MA;

%% Consider the right of a section through b-b
x2=linspace(12,20);

% Equilibrium
Vb = P2;
Mb = -60*(20-x2);

X = [x1 x2]; V = [Va Vb]; M = [Ma Mb];

subplot(211)
plot(X,V)

subplot(212)
plot(X,M)

-----------------------------
Error using plot
Vectors must be the same length.

Error in hibbler_SFBM_142 (line 32)
plot(X,V)
 

Answer 1

[Tommy]

If you look in the workspace, you should see that X has length 200 while V has length 101. If you want to plot V over X, they need to have the same length.

You create X by combining x1 and x2, both of which have length 100. Thus X has length 200.

You create V by combining Va and Vb, and while Va has length 100, Vb has length 1. Thus V has length 101.

Do you mean for Vb to equal P2 over the entire duration of x2? Then you could define it with this:

Vb = P2*ones(size(x2));

[Rovindra Nauth]

Vb equalts to P2 is the only load acting from the cut of the diagram.

I applied the Vb = P2*ones(size(x2)) code and it works. I wasn't aware I could have made that combination. Thank you for your assistance.