MATLAB: MATLAB Trapezium Rule – Input Error

functionrepeated scriptscriptscript callingtrapezium rule

Hi there,
I have written a mathematical code to calculate the trapezium rule for a set function. For my entire program, I have attempted to make it as 'user-friendly' as possible; whereby all variables are set upon running the code. This way, the script does not need to be editted in any way – see my code if you're confused in any way.
The issue I have is that when I input the actual mathematical 'function' into the program, it keeps being called multiple times, when I only want it to be called once. For example, if the function I needed evaluating was: 2x^2, I would input ' 2*x.^2 ', but would have to do this several times instead of once.
I think that the number of times the program calls upon this input is related to the number of strips to calculate – try this and see if you think I'm right? Therefore, I believe the loop inside the script keeps calling the mathematical 'function' user input continuously – I don't know how to stop this from happening?
I am a beginner to MATLAB and whilst it appears that I'm overcomplicating everything, I'm only trying to make everything as 'user-friendly' as possible…
My script: >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>.
        disp('Trapezium Rule Calculator');
        disp('Truth and Absolute Values');
        disp('-------------------------');
        disp(' ');
        % F. Variables
        a = input('Enter the value of the lower bound:');
        b = input('Enter the value of the upper bound:');
        n = input('Enter the number of strips required:');
        disp(' ');
        h = ((b - a)/ (n));
        % Summation of First and Last Tra.
        sum = 0.5*( f(a) + f(b) );
        % Loop for Middle Tra.s
        for i = 1 : n-1;
            sum = sum + f(a+i*h);
        end
        % Truth - Integral Calculation
        g = @f;
        truth = integral(g,a,b);
        disp(' ');
        disp('Actual Value of Integral:');
        disp(truth);
        % Final Value of Tra.
        Answer = h*sum;
        ModAnswer = abs(Answer);
        disp('Value of Trapezium Area Calculated:');
        disp(ModAnswer);
        % Difference (Accuracy)
        ModTruth = abs(truth);
        diff = abs( ModTruth - ModAnswer);
        disp('Difference in Calculation:');
        disp(diff);
        % Percentage Accuracy
        format short
        PInaccuracy = ( (diff) / (ModTruth) )*100;
        PA = 100 - PInaccuracy;
        disp('Percentage Accuracy (%):');
        disp(PA);
        % Functions Formulae
        function y = f(x)
        y = input('Enter function for processing:');
        end
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Please help me on how to solve this issue please?
Thank you!

Best Answer

Solved it!
The best way is to NOT use the function script at the bottom of the file...
Instead, assign a variable and use an input function along with it - see code below!
Here, adding >> @(x) << before whatever you input stores it as a function, and the following code will do its job as normal!
Thanks for your help anyways!
      disp('Trapezium Rule Calculator');
      disp('Truth and Absolute Values');
      disp('-------------------------');
      disp(' ');
      % F. Variables
      a = input('Enter the value of the lower bound: ');
      b = input('Enter the value of the upper bound: ');
      n = input('Enter the number of strips required: ');
      f = input('Enter function: [@(x)...]: ');
      disp(' ');
      h = ((b - a)/ (n));
      % Summation of First and Last Tra.
      sum = 0.5*( f(a) + f(b) );
      % Loop for Middle Tra.s
      for i = 1 : n-1;
          sum = sum + f(a+i*h);
      end
      % Final Value of Tra.
      Answer = h*sum;
      ModAnswer = abs(Answer);
      disp('Value of Trapezium Area Calculated:');
      disp(ModAnswer);
      % Truth - Integral Calculation
      truth = integral(f,a,b);
      disp('Actual Value of Integral:');
      disp(truth);
      % Difference (Accuracy)
      ModTruth = abs(truth);
      diff = abs( ModTruth - ModAnswer);
      disp('Difference in Calculation:');
      disp(diff);
      % Percentage Accuracy
      format short
      PInaccuracy = ( (diff) / (ModTruth) )*100;
      PA = 100 - PInaccuracy;
      disp('Percentage Accuracy (%):');
      disp(PA);
For example:
      Trapezium Rule Calculator
      Truth and Absolute Values
      -------------------------
      Enter the value of the lower bound: 1
      Enter the value of the upper bound: 2
      Enter the number of strips required: 16
      Enter function: [@(x)...]: @(x) 1./x
      Value of Trapezium Area Calculated:
          0.6934
      Actual Value of Integral:
          0.6931
      Difference in Calculation:
         2.4402e-04
      Percentage Accuracy (%):
         99.9648
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