I'm complitily lost with that error: Error using horzcat Dimensions of matrices being concatenated are not consistent

I have that code, to do some mathematic problem:

ER = 1.0;
EO = 8.8541e-12;
VO = 1.0;
AA = 0.001;
L = 1.0;
N = 20;
DELTA = L/N;

%--------------------------
% Matrix A
%--------------------------
I = 1:N;
Y = DELTA*(I-0.5);
for i = 1:N
 for j = 1:N
  if (i ~= j)
    A(i,j) = DELTA/abs(Y(i)-Y(j));
  else
    A(i,j) = 2.0*log(DELTA/AA);
  end
 end
end
%---------------------
% Vector B 
%-------------------
B = 4.0*pi*EO*ER*VO*ones(N,1);
C = inv(A);
RHO = C*B;
SUM = 0.0;
for I=1:N
 SUM = SUM + RHO(I);
end

Q = SUM*DELTA;
diary c:magMetMom.txt
[EO,Q]
[ [1:N] ' Y' RHO ]
diary off

%------------------
% Plot
%----------------
plot(Y,RHO)
xlabel('y (cm)'), ylabel('rho_L (pC/m)')

ERROR Message:
"ans =

     1.0e-11 *

      0.8854    0.8579

Error using horzcat
Dimensions of matrices being concatenated are not consistent."

DOES anyone can help? Tks a lot !! =))))

Answer 1

[dpb]

N = 20;
...
B = 4.0*pi*EO*ER*VO*ones(N,1);  % size(B)--> [20,1]
C = inv(A);   % size(A)--> [20,20]; ergo size(C)--> [20,20]
RHO = C*B;  % RHO-->[20x20]*[20*1]==> size(RHO)=[20,1]
...
[ [1:N] ' Y' RHO ]
...
Error using horzcat
Dimensions of matrices being concatenated are not consistent."

So, from the above you're trying to concatenate

1x20 1x2(character) 20x1 into a row vector.

Won't work. You could do

[ [1:N] RHO.' ]

but Matlab won't let you(*) mix character data in with the numeric in a single vector; you'll have to use a cell array or convert all to string format to do that.

(*) Actually, the above would work for a specific definition of "working" but it won't be what you're wanting--

>> [1:3 ' y' 2]
ans =
 y
>> whos ans
Name      Size            Bytes  Class    Attributes

ans       1x6                12  char

>>

NB: the numeric values were cast to character using their ASCII code equivalents which are non-printing characters. Similar gibberish will appear if the numeric values are floating point as in your case.

[Luiz de Souza]

humm so.. the only problem is in diary function ? I will try to have more attention next time.. and take care in output types... tks a lot

[dpb]

No, diary really has nothing to do with it; it just happens that it in this particular case you were trying to output some results but the problem is in the attempt to concatenate the row and column vectors--it's a general rule irrespective of what you're doing or where or when.