How to pass an argument for a function when it is an argument in another function?

I would like to pass a function to another function, but with a parameter for it to use. for example, I have written a cobweb function to plot a cobweb of an iterative series function. It takes a function as an argument. eg. cobweb(@sin, x0, [0 1.5 0 1.5], max_iter) returns a cobweb plot like below for repeated sin function.

However, I want to pass another function I've written, an iterative map

function x1 = it_map(x0, r)

x1 = r*x0*(1-x0);

however to do this using the same code, I'd need to pass this function in with its own argument (r), and I can't see anyway to do that.

Is there anyway to do this? or should I just fix the argument as r in the code, which is fiddly..

Answer 1

[Adam]

If r is definied beforehand you can create a function handle that turns your 2-argument function into a 1-argument function e.g.

r = 7;
f = @( x0 ) it_map( x0, r );

Then you can pass f to your cobweb function in the same way as sin because it is a function of just the one argument. This works so long as r is known before you create the function handle.

cobweb(f, x0, [0 1.5 0 1.5], max_iter)

This is a very useful 'trick' to know when you pass function handles around - the idea that you can have arguments that are 'bound' into the function at definition time and arguments that are variable to be passed in a calling time.

It means you can always change a function of n arguments into a function of < n ( or > n I suppose in the inverse case) arguments so long as you know some of them at function handle definition time.

[Jo Houghton]

Thank you for your amazingly fast answer, very helpful!

Answer 2

[Guillaume]

"Is there anyway to do this?"

Yes, it's call argument binding. In matlab, this is achieved by defining an anonymous function:

r = 5;
it_map_bound = @(x0) it_map(x_0, r);
cobweb(it_map_bound, x0, [0 1.5 0 1.5], max_iter);

Note that the anonymous function capture the value of r at creation. Changing r afterward does not affect the anonymous function.