Function Handles

Return to List of Lectures

Previous Lecture

• Questions?
• Function Handles
  • Sections 14.3 & 14.4
  • Anonymous functions in workspace
    • functionname = @(arguments) expression
  • feval function?
    • Calls function on arguments
    • feval( functionName, inputs )
    • Function handle = reference to function
      • @functionName
      • Can refer to built-in functions or user-defined ones
  • Examples
    • Function to double its argument, written anonymously
      

      >> double = @(x) 2*x
      double = 
          @(x)2*x
      >> double( 3 )
      ans =
           6
      >> feval( double, 3 )
      ans =
           6
      >> feval( 'sqrt', 9 )
      ans =
           3

    • Function that takes a function f and a value x and returns 2 f(x)
      

      function [ twof ] = doublef( f, x )
          %DOUBLEF Takes f and x as arguments and returns 2 f(x)
          twof = 2 * f(x);
      end

      
      

      >> doublef( @sin, pi/2 )
      ans =
           2
      >> doublef( @sqrt, pi/2 )
      ans =
          2.5066
      >> doublef( sin, pi/2 )
      {Error using sin
      Not enough input arguments.} 

    • Function “makeIncrementer” that takes value a as argument and returns function that adds a to its argument
      • e.g.,
        • f1 = makeIncrementer( 2 ) % f1 is function that adds 2
        • f1(3) = 5
        • f1(1) = 3
        • f2 = makeIncrementer( 17 ) % f2 adds 17
        • f2(8) = 25
        • f1(4) = 6
          

          function f = makeIncrementer( a )
              f = @(x) x + a;
          end

          
          

          >> add2 = makeIncrementer( 2 )
          add2 = 
              @(x)x+a
          >> 17^2   % add2 can run whenever wanted; unrelated stuff first doesn’t hurt
          ans =
             289
          >> add2( 3 )
          ans =
               5
          >> add17= makeIncrementer( 17 )
          add17 = 
              @(x)x+a
          >> add17( 8 )
          ans =
              25
          >> add2( 8 )
          ans =
              10

• Newton’s Method Lab
  • no syms !
• Next
  • Finish Newton lab

Next Lecture