Writing a recursive function with nested function /

Hey,

For a course project, I figured it was best to use matlab to plot a few cost functions. I've programmed before in c++ and scala, but Matlab syntax is causing me a headache. I want to plot the following function( just a line connecting the points) from 0 to 900. It's working as I want but for some reason im not able to plot it.

Basically my question is, how to plot the given function?

Help would be greatly appreciated.

function [ y] =recursiona(t) 
    total= 0;
    function y=plot(ok)
     if(ok>= 520) 
       y=50;
       return 
     end 
  
    if(ok<=0) 
      y=total;
      return
    end
    
  if(ok >= 60)  
      total =total+ 9;
      plot( ok- 60)
      
  elseif( ok <= 24)  
          total = total + 0.25 * ok;
          y= total;
          return
   
  elseif(ok >= 24 && ok <= 30 ) 
          total=total + 6;
          y=total;
          return
   
  elseif( ok > 30 && ok <= 42)  
       total =6 + (ok - 30) * 0.25;
      
  else 
   total = total + 9;
   total;
   return
  end
  
end
  plot(t)
end 

And my plotting attempt

x= 0:900;
y=recursiona(x);

plot(y,x);

I receive the following error in cmd.

Operands to the || and && operators must be convertible to logical scalar values.

Error in recursiona/plot (line 23)

elseif(ok >= 24 && ok <= 30 )

Error in recursiona (line 38)

plot(t)

Error in test (line 2)

y=recursiona(x);

[Stephen23]

"I've programmed before in c++ and scala, but Matlab syntax is causing me a headache."

Forget about C++ and Scala. To use MATLAB you need to learn how to use vecctors, matrices, and arrays. So far you are not doing this, you are trying to fit a square peg into a round hole :)

"Basically my question is, how to plot the given function?"

It has a few bugs that need to be fixed first. For example:

1. what is the valuke of y for 30<ok<60 ?
2. you will need to call the nested function with an output argument, otherwise there is absolutely no point in defining y inside that function.
3. you will need to use a loop, or use arrayfun, or vectorize your code (best):

https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html

[Aksel Bektas]

Hey, thank you for helping.

Value of y in that case should be total ( y= total)

w.r.t to you second point. I'm not sure i understood you. I am calling the function 'plot' inside the 'recursiona' function(?)

and w.r.t the third point, why my current implementation isn't adequate?

[Stephen23]

"w.r.t to you second point. I'm not sure i understood you. I am calling the function 'plot' ..."

Yes you are calling it, but without any output argument. This is how you define the function (with one output y):

function y=plot(ok)

and this is how you call the function (without any output argument):

plot(t)

You call plot with NO output argument, so any y value calculated inside the function is simply discarded.

Tip: to avoid problems later plotting data, you should avoid using the name plot.

"w.r.t the third point, why my current implementation isn't adequate? "

Within the function there is no indexing at all nor any attempt at code vectorization, so your code seems to be written on the assumption that its inputs are scalar values. If you want to apply a function that only works on scalar values to a vector of values then you will need to use a loop... or rewrite the code to work on vectors properly (best option).

As I wrote in my last comment, you need to learn how to handle vectors/matrices/arrays. That is the entire point of MATLAB.

[Walter Roberson]

https://blogs.mathworks.com/loren/2013/02/20/logical-indexing-multiple-conditions/

Answer 1

[Aksel Bektas]

Thanks again,

I got it working. There were quite a few issues, namely, that return behaves quite differently in Matlab. Apparently, if a function returns some value, it may not be written to the output of the function. Thus, I got rid of all returns. Working code below.

function [ y] =recursiona(t) 
    total= 0;
    y= plot(t);
    function as=plot(ok)
        
     if(ok>= 320) 
       as=50; 
     
  
    elseif(ok<=0) 
      as=total; 
   
    
elseif(ok >= 60)  
      total =total+ 9;
      as=plot( ok- 60);
      
  elseif( ok <= 24)  
          total = total + 0.25 * ok;
          as= total;
          
   
  elseif(ok >= 24 && ok <= 30 ) 
          total=total + 6;
          as=total;
          
   
  elseif( ok > 30 && ok <= 42)  
       total =total + 6 + (ok - 30) * 0.25;
      as=total;
  else 
   total = total + 9;
   as=total;
 end
 
    end
    
end

[Walter Roberson]

Apparently, if a function returns some value, it may not be written to the output of the function.

In MATLAB, values returned are always written to the output of the function.

The differences in that in MATLAB, return does not take an argument saying what value to return (as is the case in C). Also, functions do not return the last expression they executed (as in Maple).