MATLAB: Function having string as argument

functionsstring

Hi there,

I am making a function called 'derr' which calculates derivative of the function given in the argument as string.

function = derr('name of function');

example if 'sin' is given as argument this function should calculate derivative of sin.

calling of function should be like : derr('sin')

How can I do that?

Thank you.

Best Answer

I would not recommend using a string to define the input function.

A much more reliable way would be to write your code to accept a function handle (which is the correct variable type for holding functions):

https://www.mathworks.com/help/matlab/function-handles.html

For example, define your function something like this:

function out = myfun(fun)
assert(isa(fun,'function_handle'),'Input must be a function handle')
out = fun(pi); % do whatever you want with the function handle...
end

and then simply call your function using any function handle:

myfun(@sin)
myfun(@cos)
myfun(@sqrt)
myfun(@(n)3*(n.^2))

If you really want to limit the user to using strings (not designed for holding functions) then consider using str2func or switch inside your function.

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See this: http://www.mathworks.com/matlabcentral/answers/21111-getting-function-as-an-argument-of-function

MATLAB: How to create a “function function”? How do you make a function that accepts another arbitrary function as an input argument

'... a special type of function in MATLAB called a "function function".'

There is nothing special about a function that accepts a function handle as an input.

'How do you make a function that accepts another arbitrary function as an input argument?'

A function handle is a fundamental MATLAB data type, so they can be passed just like any other data type. Simply define your function with an input argument, and inside that function you can call that input argument as a function. For example:

function myfun(infun)
x = 0:0.1:pi;
y = infun(x);
plot(x,y)
end

and then call it with a function handle:

myfun(@sin)

A function handle is just like any other variable, you can pass it, allocated it to another variable, etc.:

f = @sin
g = f;
g(pi)

Best Answer

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