# index exceeds matrix dimensions and the toolbox code error

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Misael Tanalepy on 30 Oct 2020
Answered: Peter O on 30 Oct 2020
im so sorry, i dunno what's happening. im starting Hadi Saadat's Tolbox that talkabout IEEE 30 Bus (Power System Analyze) and doing the Gauss-Seidel iteration method with the toolbox, and then this Problem happening
% Power flow solution by Gauss-Seidel method
nbus = length(busdata(:,1));
for k=1:nbus
n=busdata(k,1);
kb(n)=busdata(k,2); Vm(n)=busdata(k,3); delta(n)=busdata(k, 4);
Pd(n)=busdata(k,5); Qd(n)=busdata(k,6); Pg(n)=busdata(k,7); Qg(n) = busdata(k,8);
Qmin(n)=busdata(k, 9); Qmax(n)=busdata(k, 10);
Qsh(n)=busdata(k, 11);
if Vm(n) <= 0 Vm(n) = 1.0; V(n) = 1 + j*0;
else delta(n) = pi/180*delta(n);
V(n) = Vm(n)*(cos(delta(n)) + j*sin(delta(n)));
P(n)=(Pg(n)-Pd(n))/basemva;
Q(n)=(Qg(n)-Qd(n)+ Qsh(n))/basemva;
S(n) = P(n) + j*Q(n);
end
DV(n)=0;
end
num = 0; AcurBus = 0; converge = 1;
Vc = zeros(nbus,1)+j*zeros(nbus,1); Sc = zeros(nbus,1)+j*zeros(nbus,1);
while exist('accel')~=1
accel = 1.3;
end
while exist('accuracy')~=1
accuracy = 0.001;
end
while exist('basemva')~=1
basemva= 100;
end
while exist('maxiter')~=1
maxiter = 100;
end
iter=0;
maxerror=10;
while maxerror >= accuracy & iter <= maxiter
iter=iter+1;
for n = 1:nbus;
YV = 0+j*0;
for L = 1:nbr;
if nl(L) == n, k=nr(L);
YV = YV + Ybus(n,k)*V(k);
elseif nr(L) == n, k=nl(L);
YV = YV + Ybus(n,k)*V(k);
end
end
Sc = conj(V(n))*(Ybus(n,n)*V(n) + YV) ;
Sc = conj(Sc);
DP(n) = P(n) - real(Sc);
DQ(n) = Q(n) - imag(Sc);
if kb(n) == 1
S(n) =Sc; P(n) = real(Sc); Q(n) = imag(Sc); DP(n) =0; DQ(n)=0;
Vc(n) = V(n);
elseif kb(n) == 2
Q(n) = imag(Sc); S(n) = P(n) + j*Q(n);
if Qmax(n) ~= 0
Qgc = Q(n)*basemva + Qd(n) - Qsh(n);
if abs(DQ(n)) <= .005 & iter >= 10 % After 10 iterations
if DV(n) <= 0.045 % the Mvar of generator buses are
if Qgc < Qmin(n), % tested. If not within limits Vm(n)
Vm(n) = Vm(n) + 0.005; % is changed in steps of 0.005 pu
DV(n) = DV(n)+.005; % up to .05 pu in order to bring
elseif Qgc > Qmax(n), % the generator Mvar within the
Vm(n) = Vm(n) - 0.005; % specified limits.
DV(n)=DV(n)+.005; end
else, end
else,end
else,end
end
if kb(n) ~= 1
Vc(n) = (conj(S(n))/conj(V(n)) - YV )/ Ybus(n,n);
else, end
if kb(n) == 0
V(n) = V(n) + accel*(Vc(n)-V(n));
elseif kb(n) == 2
VcI = imag(Vc(n));
VcR = sqrt(Vm(n)^2 - VcI^2);
Vc(n) = VcR + j*VcI;
V(n) = V(n) + accel*(Vc(n) -V(n));
end
end
maxerror=max( max(abs(real(DP))), max(abs(imag(DQ))) );
if iter == maxiter & maxerror > accuracy
fprintf('\nWARNING: Iterative solution did not converged after ')
fprintf('%g', iter), fprintf(' iterations.\n\n')
fprintf('Press Enter to terminate the iterations and print the results \n')
converge = 0; pause, else, end
end
if converge ~= 1
tech= (' ITERATIVE SOLUTION DID NOT CONVERGE'); else,
tech=(' Power Flow Solution by Gauss-Seidel Method');
end
k=0;
for n = 1:nbus
Vm(n) = abs(V(n)); deltad(n) = angle(V(n))*180/pi;
if kb(n) == 1
S(n)=P(n)+j*Q(n);
Pg(n) = P(n)*basemva + Pd(n);
Qg(n) = Q(n)*basemva + Qd(n) - Qsh(n);
k=k+1;
Pgg(k)=Pg(n);
elseif kb(n) ==2
k=k+1;
Pgg(k)=Pg(n);
S(n)=P(n)+j*Q(n);
Qg(n) = Q(n)*basemva + Qd(n) - Qsh(n);
end
end
Pgt = sum(Pg); Qgt = sum(Qg); Pdt = sum(Pd); Qdt = sum(Qd); Qsht = sum(Qsh);
clear AcurBus DP DQ DV L Sc Vc VcI VcR YV converge delta Peter O on 30 Oct 2020
I'd guess that n is larger than the size of P. In the first couple lines it seems that P only gets allocated if the swing angle is in the wrong half of the plane (generator vs motor). If nbus exceeds the last n where this condition hits (e.g. nbus is 8 and the last time the ELSE runs is n=7), then the error could occur. And some of the P values will be missing. I'm guessing it might load in P prior, with busdata? Alternatively it's a typo and those lines should be located outside the ELSE condition.
If you toss a debug breakpoint before it enters into the Gauss-Seidel loop, what's it report for the size of P and the value of nbus? That will help us diagnose.
This code could be formatted more cleanly, especially with respect to the indent style, but it's common to see IF statements and multi-assignment lines in example textbook code since otherwise it can take too many pages to print! It could also be refactored to take advantage of MATLAB's vectorization operations. (Probably ported from C or FORTRAN originally)

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