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.

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)

Answer 1

[Mischa Kim]

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)

[jayash]

Thanks man!! :) Can you give brief explanation??

[Mischa Kim]

 a = [1 2 10];
 b = diff(a)
 b =
     1     8

As explained above, diff computes the differene btw. vector elements. Therefore, b (in this case) only has two elements, not three.

[Jose Cruz]

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

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