Vector imbalance error in while loop

      I am trying to plot based on a certain situation. In the first to situation (Beam. Load == 1 and Beam.Support == 1) and (Beam. Load == 1 and Beam.Support == 2), I need to create two sets of y values and two sets of x values and then join them together such that x1 is the x values and y is y values. When I run this script in MATLAB the other cases work, but not the one stated above. Instead MATLAB returns the error:

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

Error in Beam_Deflection_GUI>process (line 395)
                y1(i) = (F.*x.^2/6*E*I).*(3*a-x);     % 0<x<a

Error while evaluating uicontrol Callback

Here is the Code:

 I = Beam.Inertia;
      a = Beam.Location;
      F = Beam.Magnitude;
      L = Beam.Length;
      b = Beam.Length-Beam.Location;
      x = linspace(0,Beam.Length);
      o = Beam.Magnitude/Beam.Length;   % Magnitude is them same as the force
      y1 = zeros(1,100);
      y2 = zeros(1,100);
      x1 = zeros(1,100);
      x2 = zeros(1,100);
      i = 1;
      Beam.x1 = x;

      if Beam.Load == 1 % Referring to the point in the list during the selection
          if Beam.Support == 1 
              while x(i) < a
                  y1(i) = (F.*x.^2/6*E*I).*(3*a-x);     % 0<x<a
                  x1(i) = x(i);
                  i = i + 1;
              end
              while x(i) <= L && x(i) < a
                  y2(i) = (F.*a^2/6*E*I).*(3*x-a);      % a<x<L
                  x2(i) = x(i);
                  i = i+1;
              end
              Beam.y1 = [y1, y2];
              Beam.x1 = [x1, x2];
          else  % x.Support == 2
              while x(i) < a
                  y1 = (F*b.*x/6*L*E*I).*(L^2-x.^2-b^2);                  % 0<x<a
                  i = i+1;
                  x1 = x(i);
              end
              while x(i) <= L
                  y2 = (F*b/6*E*L*I).*((L/b).*(x-a).^3+(L^2-b^2).*x-x.^3);% a<x<L
                  i = i+1;
                  x2 = x(i);
              end
              Beam.y1 = [y1, y2];
              Beam.x1 = [x1, x2];
          end
      else    % x.Load == 2
          if Beam.Support == 1
              Beam.y1 = (o.*x.^2/24*E*I).*(x.^2+6*L^2-4*L.*x);
          else % x.Support == 2 
              Beam.y1 = (o.*x.^2/24*E*I).*((L^3-2*L.*x.^2)+x.^3);
          end
      end

Answer 1

[Matt Fig]

You may have meant:

y1(i) = (F.*x(i).^2/6*E*I).*(3*a-x(i));     % 0<x<a

Otherwise you are trying to put numel(x) elements into a single element of y1.

[Lawson Hoover]

I have that portion working now but now, when I have Beam.Support == selected in the second while loop, I get the error:

Attempted to access x(101); index out of bounds because numel(x)=100.

Error in Beam_Deflection_GUI>process (line 415)
                x2 = x(i);

Error while evaluating uicontrol Callback

Even though I do not think that I am telling it to even access the value 101.

[Walter Roberson]

If all of the x(i) < L then you "run off the end" of x. You increment i and blindly use x(i) without checking to see if the new "i" is after the end of "x".

[Matt Fig]

It would be better to check that your increment variable (i) is not larger than the length of the vectors involved.

X = [1 5 2 4 3];
L = length(X);
ii = 1;
while ii<=L
   X(ii) = X(ii) + 10;
   ii = ii + 1;
end
X

But, if you know you are just going to increment through the vector elements, why not use a FOR instead?

X = [1 5 2 4 3];
for ii = 1:length(X)
   X(ii) = X(ii) + 10;
end
X

Answer 2

[Walter Roberson]

Your loop is while x(i) < a implying that x is a vector. But then you have

y1(i) = (F.*x.^2/6*E*I).*(3*a-x);

and if x is a vector then the result of the calculation is going to be a vector, and you then try to store that vector into the single result y1(i) .

Perhaps you want

y1(i) = (F.*x(i).^2/6*E*I).*(3*a-x(i));

and similar fixes in other lines.

Answer 3

[Lawson Hoover]

Ok I have fixed the first issue but now I am receiving the error:

Attempted to access x(101); index out of bounds because numel(x)=100.

Error in Beam_Deflection_GUI>process (line 415)
                x2 = x(i);

Error while evaluating uicontrol Callback

I have turned the all the x into x(i) but I still get that error. Any ideas?