Converting an old Matlab code from 2011 to work with newest version

Hello all

I have very limited Matlab skills as I have used it just couple of times in some courses and mainly for running some premade code. Now however, our paths crossed again and this time for personal hobby project. I am in progress of building a xylophone/marimba for my kid, who has shown some interest in musical instruments. There is a remarkably good xylophone building blog post that I have been reading, which goes through the project in great detail. This blog mentions a Master’s thesis project that focuses on calculating the shape of the curved under side for each bar so that they will produce harmonic timbre. The blog doesn’t include the code itself, but guides the reader to the thesis, which can be found here. The full code is included in the appendix section. I made a pdf to text conversion for the code, fixed the most obvious conversion errors and some warnings that Matlab gave, but there are some functions that my beginner skills cannot handle. I will post those tricky parts here as it was not good practice to paste the whole project. I would greatly appreciate any help and I hope this would also help others.

I currently have Matlab R2020b installed on my work computer, but I can update it to R2022b once I will be back in uni network in early January.

Blog post

Zhao Mingming's Master's thesis: Automatic Multi Modal Tuning of Idiophone Bars

The pdf to text converted code is in the attachments

The first tricky part is on the page 125 of the thesis, in while loop that begins from the previous page

while any(abs(df)>tol) 
    
    %displys the resulted natural frequencies 
    frequency_old=eval([method'(profile,coeffs,E,G,rho,x_section,nu,d0,width,bar_length,number_of_elements,tol,number_fn,ploton)']); 
    slope=[]; 
    
    %for the first three natural frequencies    
    for k=1:3 
        coeffs_new=coeffs; 
        coeffs_new(k)=coeffs_new(k).*delta_a; 
        frequency_new=eval([method'(profile,coeffs_new,E,G,rho,x_section,nu,d0,width,bar_length,number_of_elements,tol,number_fn,ploton)']) 
        slope=[slope (frequency_new-frequency_old)./(coeffs_new(k)-coeffs(k))]; 
    end 
    df=frequency_required-frequency_old;  
    da=(slope)\df; 
    coeffs=coeffs+da; 
end 

I get the following error. I have tried to fix it myself, but no luck so far. This eval([method... appears many times in the program so I think it will get me going if I know how to fix it.

frequency_old=eval([method'(profile,coeffs,E,G,rho,x_section,nu,d0,width,bar_length,number_of_elements,tol,number_fn,ploton)']);

↑

Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

Answer 1

[Stephen23]

"I have very limited Matlab skills ..."

Don't learn from that badly-written code. Use function handles!

"This eval([method... appears many times in the program so I think it will get me going if I know how to fix it."

The shown code would also throw an error in earlier versions, so it is possible it was transcribed incorrectly: my guess is that there was a space or comma between METHOD and the following character vector:

[method,'(profile,coeffs,...etc...number_fn,ploton)']
%      ^ missing comma

But you should avoid writing/copying code that uses EVAL() to perform basic tasks like this.

Better:

A much better approach is to call FEVAL() like this:

frequency_old = feval(method, profile,coeffs,E,G,rho,x_section,nu,d0,width,bar_length,number_of_elements,tol,number_fn,ploton);

Best:

Using a function handle will make your code more robust and much more efficient than that badly-written code:

https://www.mathworks.com/help/matlab/function-handles.html

https://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html

For example, in that Mfile you should replace this line (assuming that METHOD_TIMOSHENKO is a function):

method = 'Method_Timoshenko'; % needs to be EVALed later... ugh :(

with this function handle:

method = @Method_Timoshenko; % this defines a function handle!

and then later replace that ugly evil EVAL() call with this much more efficient, more robust, simpler code:

frequency_old = method(profile,coeffs,E,G,rho,x_section,nu,d0,width,bar_length,number_of_elements,tol,number_fn,ploton);

Note how the function handle can be simply called, just like other functions.

[Lauri Paulamäki]

Thank you very much for your swift and helpful reply. I'll try to digest this information and ask again if I don't get it.