# I am getting this error- "Vectors must be the same lengths.". Also please explain why its showing this error as I am plotting a funtion with 'x' as variable with defined vector.

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jayash on 23 Jun 2014
Commented: Jose Cruz on 21 Sep 2019
clear all
rr=0.99997622; % reflectivity of the cavity
r=sqrt(rr);
finesse=pi.*sqrt(rr)./(1-rr); % finesse of the cavity
fsr=10^9;
x=-9e4:10:9e4; % frequnecy detuning
z=x./fsr;
FWHM=fsr./finesse;
mod=40e6; % modulation frequency to the laser
m=mod./fsr;
g=r.*(exp(((x./fsr).*(2.*pi)).*1i)-1)./(1-(r.^2).*exp(((x./fsr).*(2.*pi)).*1i));
abg=abs(g);
sg=power(abg,2);
dfg=diff(sg);
y=m.*dfg;
plot(x,y)

Mischa Kim on 23 Jun 2014
Edited: Mischa Kim on 23 Jun 2014
Jayash, with the diff command you compute the difference between elements in a vector thereby reducing the number of elements by one. Use instead
plot(x(2:end),y)
Jose Cruz on 21 Sep 2019
Mischa,
What if my problem is similar but 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?
Matrix dimensions must agree.
Error in homework_1_P2 (line 40)
Inertia = (1.1*Mv*(dVdt).*V)./1000; % kW
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
Inertia = (1.1*Mv*(dVdt).*V)./1000; % kW

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