function d2Qdt2 = EExtra_VarCorr( Q, V )
% Solution to problem 4 of ConvExtra. JMS, Jun.2024
% Input:
%   Q(2,1) : condenser charges (C)
%   V      : source potential (V)
% Output:
%   d2Qdt2(2,1) : second charge derivatives d2Q/dt2 (C/s^2)

C1 = 1e-4;    % 1st capacitance (F)
C2 = 7.5e-5;  % 2nd capacitance (F)
L1 = 1e-7;    % 1st self inductance (H)
L2 = 3e-8;    % 2nd self inductance (H)
M = 2e-8;     % mutual inductance (H)

d2Qdt2(1) = ( (Q(1)/C1-V)*L2 +  Q(2)/C2   *M ) / (M^2-L1*L2);
d2Qdt2(2) = (  Q(2)/C2   *L1 + (Q(1)/C1-V)*M ) / (M^2-L1*L2);

end
