Getting an error : In an assignment A(:) = B, the number of elements in A and B must be the same.

% Load the converted TDMS file into matlab
load('TEST_2017_12_04_11_25_51.mat')
Force=ConvertedData.Data.MeasuredData(15).Data; % Input Force values into F
F=Force.';% Transpose matrix for Force for RBF calculation
dis=ConvertedData.Data.MeasuredData(9).Data  ; % Input Displacement values into dis
N=1; 
for m=1:length(F)  % Find Number of displacement per Force and assign it to Dis
  for n=1:(length(dis)/length(F))
      Dis(m,n)=dis(N);
      N=N+1;;
  end
end
DIS=Dis.'; % Transpose matrix for mean displacement calculation
mean_dis=mean(DIS); % Calculate mean dispalcement value

%Input first sensor position and bearing position

% Fir_sen=input(' Input the First sensor position');
% 
% Bear_pos=input(' Input the bearing position');

%input calculated radial force values solve equations
val=zeros(1,708);
j=1;

for m=1:(length(F))
    a=F(m);
    syms RBF;
    syms BSBF;
    % solve the equations and find radial bearing load
    % F= applied load. RBF= roller bearing force .  
    % BSBF= back support bearing force 

      eqn1=(331.5*a)-(RBF*231.5);
      eqn2=(BSBF * 231.5)+(100*a);
      sol=solve(eqn1,eqn2);

    val(j)=(double (sol.RBF)); % * _*** This statement is the problem ***_*
    j=j+1;

end
disp('New calculated radial force values');
disp(valueofRBF);

why am i getting this error ? 'In an assignment A(:) = B, the number of elements in A and B must be the same' ?

[Adam]

doc debugging

Learn to use the debugger, especially the Stop/Pause on Errors option and these kind of things become trivial to locate, in combination with some quick command line checks once your are stopped at the error.

Also please format all your code correctly in future as it is unreadable otherwise.

The error you are getting tells you that the size of what you are trying to assign ( sol.RBF ) is different to the size of what you are trying to assign it to ( val(j) ). val(j) is clearly a scalar so sol.RBF evidently isn't in some or all cases. My Matlab doesn't have a 'solve' function so I have no idea what it should return, if it is a toolbox function or one of your own.

[Arun Chellappan]

It is a toolbox function. I knew that error states the elements on RHS and LHS is not same. But logically i input one force and RBF corresponding to that force is calculated. That is assigned to val(j).

[Karan Gill]

I think the reason Adam posted that comment because using the debugger will actually let you check the values in question. Further, also because you did not post the actual error. So we don't know where the error occurs. No one will realize you added a comment for the line in question.

[Arun Chellappan]

The error is :

_ In an assignment A(:) = B, the number of elements in A and B must be the same._

Answer 1

[David Goodmanson]

Hi Arun,

Have you checked the value of RBF? I think it's quite likely that since you have supplied the value of 'a', you are attempting to solve three equations in the two unknowns RBF and BSBF. Not a great idea. You might get a result like " RBF = 0×1 empty double column vector ". (It's true that the third equation is redundant, since it is a consequence of the other two. So you should be able to "solve" all three of them at once. But it doesn't always work out that way in practice). Anyway, if this does turn out to be the the problem, why use syms at all? Algebra works.

RBF = a*331.5/231.5;     BSBF = a - RBF;

[Arun Chellappan]

Hi David,

I think there is no problem with equations. because i tried removing the assigning part and this worked. I think the problem is with assigning. Also i have another code with 4 equations.Then i cannot follow the suggested method.

[Arun Chellappan]

I changed to two equations but still the error is shown

[David Goodmanson]

That's interesting, because when I supply a value for 'a', make a simple val array and try to solve the three equations I get that exact error message, and reverting to just two equations (as you did in the question) works. Different results for you, so the real answer must be elsewhere. What is the value of sol.RBF when the error occurs?

[Arun Chellappan]

Thanks David. This works

Answer 2

[Walter Roberson]

You use solve(l, which requests that all closed form solutions be found, and in the case of polynomials that all roots be found. But your code assumes that exactly one solution is found. You should examine sol.RBF to see how large it is. Perhaps you could use eliminate some of the possible solutions by adding assumptions to the variables such as

syms RBF positive

[Arun Chellappan]

Tried . Did not work