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8.1.2: User-Defined Functions of Vectors Examples and Exercises

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      By Carey Smith

      Example \(\PageIndex{1}\) my_min_cs


      MATLAB has a built-in minimum function, of course. This example shows how you could write your own minimum function. This kind of logic might be applied to other kinds of searches of a data vector. This algorithm works on a vector input only. It returns both the minimum value and its index.

      A key idea is to use the first element of the vector as a candidate for the minimum value, then search for values less that the candidate value. If such a value is found, then the new, smaller value replaces the candidate value .

      function [x_min, k_min] = my_min(x)
      % Input:
      % x = data vector (1xn or nx1)
      % Outputs:
      % x_min = the minimum value of x
      % i_min = the index of the minimum value of x
      x_min = -inf;
      k_min = -1;

      % Is x 1-Dimensional?
      [m_rows, n_cols] = size(x);
      % If both the number of row and
      % number of columns are > 1,
      % then the vector is 2D
      if( (m_rows > 1) & (n_cols > 1) )
          disp('Error: input is not 1-Dimensional');
      % If it get this far, then the vector is 1-Dimensional
      k = 1; % 1st index into the input vector
      x_min = x(k); % Initialize the min value to the first value
      k_min = k;
      n = length(x);
      % This loop compares each value to the current min.
      for k= 2:n % Start with k=2, because we initialed to k=1
          if(x(k) < x_min) % Is this value bigger than min so far?
              x_min = x(k); % Reset the min so far to this value
              k_min = k;

      end % end of function


      Try testing it with this input vector:

      x = [3,2,3,5,6,4,1,4]
      [x_min, idx_min] = my_min(x)


      Exercise \(\PageIndex{1}\) my_max

      Modify the my_min example function to create a function m-file that finds the maximum of a vector input.


      Add texts here. Do not delete this text first.


      This page titled 8.1.2: User-Defined Functions of Vectors Examples and Exercises is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Carey Smith.