Error: Matrix dimensions must agree

I need to multiply the Diff () = dVdt [1369 x 1] with V [1370 x 1] equation. How can I add to the lenght of dVdt? I need to add three terms together and their Matrix Dimeions must match. See error below:

Matrix dimensions must agree.

Error in homework_1_P2 (line 40)

Inertia = (1.1*Mv*(dVdt).*V)./1000; % kW

load CYC_FUDS.mat
t = cyc_mph(:,1);           % Time [s]
Vmph = cyc_mph(:,2);        % Velocity [mph]
V = Vmph.*(1609/3600);      % Velocity [m/s]
dVdt = (diff(V)./diff(t));                         % Accel. m/s^2
% Aerodynamic = (0.5*pa*Cd*Af*V.^3)./1000;         % kW
% Rolling = ((Cr*Mv*g*cos(Xa)).*V)./1000;          % kW
Inertia = (1.1*Mv*(dVdt).*V)./1000;                % kW
% Pw = (Aerodynamic+Rolling+Inertia);              % kW

Answer 1

[James Tursa]

You could use V(2:end) or V(1:end-1) instead of V in that line. Or maybe average the two.

[Jose Cruz]

Thank you, this works! I realized with your anwer that I should use V(1:end-1) throught all my equations.

[Walter Roberson]

gradient()

[Jose Cruz]

Is gradient meant to be used with funtions or will it work with numerical (emperical) values loaded from .mat?

[Walter Roberson]

There are two versions of gradient(). One of them works with symbolic functions or symbolic expressions; the other works with numeric matrices.

[Jose Cruz]

Thank you! I'll have to try with the gradient and see how it compares to using V(1:end-1).