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How does feval work in MATLAB?

  1. Jan 30, 2010 #1
    I'm completely new at MATLAB, having just started using it about a week ago. In an assignment of mine, I have to make a function that does bisection. So I pass a function, along with a set of bounds, to the function I wrote.

    The thing is, I can't figure out how to make my function accept the function I'm trying to input into it. I was told I could use

    feval ( function-name , x-value )

    to find the value of a function at a particular x value, but I could not, for the life of me, figure out how I can make feval recognize functions. I tried passing strings, names of other simple functions I made, and just about everything I could think of. Nothing works.

    Then I tried looking online, and websites and MATLAB's built-in help confused me even more by telling me stuff about "function handles" and "@" signs.

    So could someone please explain to me, in the simplest language possible, how feval works? I would be very, very grateful.
  2. jcsd
  3. Jan 30, 2010 #2


    User Avatar
    Gold Member

    If the function you want to call is 'compute' you'd enter '@compute' as the argument
  4. Jan 30, 2010 #3
    But I have something like this

    function returnvalue = bisectionfunc ( function_name , upper_bound, lower_bound )

    blah blah blah


    feval ( function_name , value_of_variable );

    What do I pass into bisectionfunc as "function_name"? I'd like that to be the function on which I'm performing the bisection method.
  5. Jan 30, 2010 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    The simple answer: Pass @function_name to bisectionfunc. feval wants a function handle, not a function name.
    Code (Text):
    function bisectionfunc(fhandle,upper_bound,lower_bound)
      feval (fhandle, value);
    That said, you could make your function take the name of a function as an argument as well as a function handle:
    Code (Text):
    function bisectionfunc(fhandle,upper_bound,lower_bound)
      if ischar(fhandle)
        fhandle = str2func(fhandle);
      feval (fhandle, value);
  6. Jan 30, 2010 #5
    Ahh, I think I got it. I passed the name of the mathematical function as a string to the function I wrote, and somehow it works.

    Still not sure why it works, but thanks everyone for your help.
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