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

%%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??

[Stephen23]

Do not redefine pi like this:

 pi=3.14;

The inbuilt value is much more precise

 >> pi
 ans =
          3.14159265358979

Answer 1

[Stephen23]

"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

[Guillaume]

To Rohan's defense, inputdlg documentation is one of these old style documentation pages that are absolutely useless at actually documenting the inputs and outputs of the function.

In this particular case, it's only in the tip section that you're actually told that inputdlg returns a cell array. Not at all, where you'd expect to find that information so it's understandable that you'd assume that inputdlg works the same as input.

That documentation is additionally bad in that it recommends using str2num on user input without any warning about the dangers that come with it.

[Stephen23]

@Guillaume: I agree that the inputdlg documentation is not totally clear. That is why I listed some of the other trivial ways that users can check variables, e.g. looking at them in the variable viewer, and using the class operator.

MATLAB has one of the easiest and most intuitive workspaces of any IDE that I know, with easy access to viewing and checking values. Beginners need to learn to use it.

[Rohan Maharjajn]

Thank you @Stephen Cobeldick and @Guillaume for the help. now i am having trouble publishing the file as i have codes to be evaluated..

Index exceeds matrix dimensions.

Error in eg9copy (line 22)

l = vec(1);

[Stephen23]

@Rohan Maharjajn: if the user clicks the dialog cancel button then the output of inputdlg will be an empty cell array. Then the numeric vec will also be empty and you will get the error that you are showing us. You will need to decide what you want your code to do when the user clicks cancel, and then add some statements (e.g. an if statement) to do whatever you need it to do.

If the user has entered an invalid input (not a number, or empty) then str2double will convert this to NaN. You will need to decide how to handle NaNs.

If the user has provided all valid numbers then my code works perfectly. I know this because I tested it, and read the documentation carefully for the functions that I used. If it does not work for you then please post the complete code that you are using and the complete error message (all of the red text).

[Rohan Maharjajn]

@Stephen Cobeldick Actually the dialogue box would appear again and again so I clicked the cancel button.I have attached the m file that i am trying to execute.Hop you will have a look at it and help run this code. The following error showed up this time.

Error using evalmxdom>instrumentAndRun (line 116)

Publishing a script that contains a publish function is not supported.

Error in evalmxdom (line 21)

[data,text,laste] =instrumentAndRun(file,cellBoundaries,imageDir,imagePrefix,options);

Error in publish (line 189)

    dom = evalmxdom(file,dom,cellBoundaries,prefix,imageDir,outputDir,options);

Error in eg9copy (line 185) publish('eg9copy.m','evalCode',true)

[Stephen23]

You got yourself into an infinite loop, caused by your last line:

 publish('eg9copy.m','evalCode',true)

When you call publish on that line it runs the whole script again, and then when that gets to the publish it runs the whole script again, and then when that gets to the publish it runs the whole script again, and then when that gets to the publish it runs the whole script again...

If you do not wish to get into an infinite loop then do not call your script inside itself.

I would recommend that you learn to write functions instead of scripts. Then you can easily avoid this kind of problem:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

And read my answer again.

[Rohan Maharjajn]

@Stephen Cobeldick, I have used function but now I have no idea how to publish the report..

[Stephen23]

@Rohan Maharjajn: the script eg9copy.m is not a function and it still has publish() at the end, which will cause the same problem: you will get into the same infinite loop. Think about it. Also if you define your own function called publish then you will not be able to call the MATLAB publish function.

Really you need to get rid of any mention of publish in eg9copy.m otherwise there will be an infinite loop. I will have to keep saying this until you remove it. Also get rid of that badly named publish file. Call publish from the command line:

 publish('eg9copy.m','evalCode',true)

Although personally I have never called the publish function: I simply click the button in the ribbon:

[Rohan Maharjajn]

@Stephen Cobeldick Thank you very much for your help and guidance. I was able to publish the result from the command prompt. But, is there any way I can publish it from the editor? while doing so , I was again stuck in an in finite loop. I have made all the corrections you told me .

[Stephen23]

"is there any way I can publish it from the editor?"

Of course you can do this: publish can be called in any script or function. Just remember that if you call publish inside the same function that you are publishing then you will always get into an infinite loop. So call it from another script or function.