Possible to use anonymous function as script function input?

Hey everyone!

I was wondering if there is any method to allow anonymous function to be used as an input. For example:

I have the following script:

function output = exampleF(input)
output = 3*input

And then use sin(x) as an input:

exampleF(sin(x))

By doing it like that I would get that x is not a defined variable.

Is there any way to program 'sin(x)' as an anonymous function ? in a same manner as

 f = @(x) sin(x).

Thank you for your time!

Answer 1

[Matt Fig]

function output = exampleF(input)
output = @(x) 3*input(x);

Now from the command line:

T = exampleF(@(x) sin(x));
T(pi/2)

[Kokalz]

Is there any way to avoid using '@(x)' when using the function in the command line? Like that:

 T = exampleF(sin(x));
 T(pi/2)

[Daniel Shub]

This works if input only takes one argument. What about if it takes multiple arguments?

[Matt Fig]

Kokalz, when MATLAB sees:

sin(x)

if first looks to see if sin is a local variable in order to index it with variable x. If not, then it looks to see if sin is a function and tries to pass it the argument x. Since you have not defined x, you get the error.

Now look at how MATLAB itself deals with the problem. When you call FZERO, you pass a function handle. When you call FSOLVE, LSQNONLIN, LSQCURVEFIT, ODE45, or most any other solving function in MATLAB, you pass in a function handle. So why do you want to code so differently than users of MATLAB are used to doing??

[Matt Fig]

Having said that, you can use the older, less recommended method of using strings:

function output = exampleF(input)
output = inline(['3*',input]);

Now from the command line:

T = exampleF('sin(x)');
T(pi/2)

Answer 2

[Walter Roberson]

exampleF(@(x) sin(x))

However, you will find that multiplying a function handle by a constant is not allowed.

Is your desired output a numeric value or a new function handle ?

[Kokalz]

I am trying to write a function that would solve equations by using Newton-Raphson method. So I was wondering if it is possible to allow user input the function simply as 'sin(x)' and then do all the newton-raphson method steps with that function.

[Walter Roberson]

Yes if you include the apostrophes, such as

exampleF('sin(x)')

Equivalent would be using command form,

exampleF sin(x)

but that would not be able to return a value to a variable.

It is not possible to write

exampleF(sin(x))

without having the sin(x) be evaluated before being passed in to exampleF

Answer 3

[per isakson]

See:

• MATLAB's advanced language features empower scientific programmers.
• Thoughts about Anonymous Functions
• NestFun.ppt