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Error: Matrix dimensions must agree

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Jose Cruz
Jose Cruz on 21 Sep 2019
Commented: Jose Cruz on 21 Sep 2019
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

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Accepted Answer

James Tursa
James Tursa on 21 Sep 2019
Edited: James Tursa on 21 Sep 2019
You could use V(2:end) or V(1:end-1) instead of V in that line. Or maybe average the two.

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Jose Cruz
Jose Cruz on 21 Sep 2019
Is gradient meant to be used with funtions or will it work with numerical (emperical) values loaded from .mat?
Walter Roberson
Walter Roberson on 21 Sep 2019
There are two versions of gradient(). One of them works with symbolic functions or symbolic expressions; the other works with numeric matrices.
Jose Cruz
Jose Cruz on 21 Sep 2019
Thank you! I'll have to try with the gradient and see how it compares to using V(1:end-1).

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