MATLAB: Undefined operator ‘*’ for input arguments of type ‘cell’. Error in eg9copy (line 23) RBV=((Vc*l​1+Vd*((l-l​2)/l)))

cellundefined operator

%%This program can be used to calculate the deameter of a shaft with two %%pulleys
%% Taking inputs for the variables of the pulleys and the shaft
clc a=42; %allowable shear stress
pi=3.14;
b=63; %allowable working stress
l= inputdlg('enter the span of the shaft l=');
d1= inputdlg('enter the diameter of the first pulley from the left d1(in m)=');
l1= inputdlg('enter the distance of the first pulley from the left l1(in m)=');
d1= inputdlg('enter the diameter of the second pulley from the left d2(in m)=');
l2= inputdlg('enter the distance of the second pulley from the right l2(in m)=');
Vc= inputdlg('enter the vertical load on first pulley Vc=');
Hc= inputdlg('enter the horizontal load on first pulley Hc=');
Vd= inputdlg('enter the vertical load on second pulley Vd=');
Hd= inputdlg('enter the horizontal load on second pulley Hd=');
%let RA and RB be the reactions at the bearing positions
%% For the vertical loading
RBV=((Vc*l1+Vd*(l-l2)/l))
fprintf('Vertical reaction at B=%4.2f N\n',RBV)
RAV=(Vc+Vd-RBV)
fprintf('Vertical reaction at A=%4.2f N\n',RAV)
%% For vertical bending moment
Mav=0; Mbv=0;
Mcv=RAV*l1;
fprintf('the vertical bending moment at C=%4.2f\n',Mcv)
Mdv=RBV*l2;
fprintf('the vertical bending moment at B=%4.2f\n',Mdv)
How can I solve this problem??

Best Answer

"How can I solve this problem"
If you had read the inputdlg documentation then you would know that inputdlg returns a cell array containing the selected values: "The returned variable answer is a cell array containing one answer per text entry field"
Is a cell array containing strings the same a numeric array?
Can we do numeric operations on a cell array, or on a numeric array?
(hint: look for the word "numeric")
The warning message tells you that there is a cell array. Did you check this? This is something else the beginners need to learn: instead of writing code and having no idea what it is doing, they need to learn to understand what every line is doing, and they need to make sure that it does what they want, and that this means checking what they code is actually doing, not just what they think it is doing. Write every line and then test that line to make sure that it does exactly what you need it to do.
MATLAB has lots of ways to help you do this, for example the great documentation, and a very convenient workspace viewer. Simply looking at the workspace would have told you that these variables are cell arrays and not numeric arrays.
To fix your code convert the string values to a numeric using str2double:
>> C = inputdlg('enter the span of the shaft l=')
C = 
    '5'
>> class(C)
ans =
cell
>> N = str2double(C{1})
N = 
     5
>> class(N)
ans =
double
Also note that it is a very bad idea to redefine pi, especially with such an imprecise value like 3.14. The inbuilt value of pi is much higher precision:
 >> pi
 ans =
          3.14159265358979
Also note that you can get rid of the multiple dialog boxes with just one:
pmt = {'enter the span of the shaft l=',...
  'enter the diameter of the first pulley from the left d1(in m)=',...
  'enter the distance of the first pulley from the left l1(in m)=',...
  'enter the diameter of the second pulley from the left d2(in m)=',...
  'enter the distance of the second pulley from the right l2(in m)=',...
  'enter the vertical load on first pulley Vc=',...
  'enter the horizontal load on first pulley Hc=',...
  'enter the vertical load on second pulley Vd=',...
  'enter the horizontal load on second pulley Hd='};
out = inputdlg(pmt);
vec = str2double(out);
%
l  = vec(1);
d1 = vec(2);
l1 = vec(2);
etc
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