Passing a function as an argument into another function won't compile without using quotes ''?

Question

When I pass a function (let's call it f) into my Base function , the Base function doesn't recognize the f function , without using '' quotes , here's the code :

function y = test(a, b, n ,f)

if ( rem(n,2) ~= 0 )
   error ( 'n is not even' )
end

% create a vector of n+1 linearly spaced numbers from a to b
x = linspace ( a, b, n+1 );

for i = 1:n+1
    % store each result at index "i" in X vector
    X(i) = feval ( f, x(i) );
end
y=sum(X);
end

And this is f.m :

function [y] = f (x)
y = 6-6*x^5;

When I run from command line with quotes :

>> [y] = test(0,1,10,'f')

y =

   52.7505

but when I remove them :

>> [y] = test(0,1,10,f)
Error using f (line 2)
Not enough input arguments.

Where is my mistake ? why can't I execute [y] = test(0,1,10,f) ?

Thanks

Your code as written, and as the error suggests, is trying to evaluate the function `f` and pass the result into the function test. — Edric, Jun 22 '12 at 11:20

H.Muster · Accepted Answer · 2012-06-22T11:27:41.070

3

The function feval expects either the function name (i.e., a string) or a function handle as input. In your code, f is neither a name, nor a handle. Use either the string 'f' or the handle @f when calling your base function test.

If, as posted in the comments, function handles are not allowed per assignment in the call to the base function, you can still use the function handle to create a string with the name of the function. This functionality is provided by the function func2str:

functionName = func2str(@f); 

test(0,1,10,functionname);

edited Jun 22 '12 at 11:27

answered Jun 22 '12 at 09:36

H.Muster

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I can't pass `@f` (assignment rules) , I need to pass only `f` , any other suggestion maybe ? – JAN Jun 22 '12 at 10:50
1

What do you mean by 'assignment rules'? Passing `@f` is the correct thing to do here. In other words, `test.m` is fine, you need to invoke it as `test(0,1,10,@f)`. – Edric Jun 22 '12 at 11:21
@ron Are function handles prohibited in general or just in the call to `text()`? – H.Muster Jun 22 '12 at 11:23
@H.Muster: Just in the call of `test(...)` . Please note that I can always do this : `q = @(x) 6*x^2 +1` and then execute `test()` like this : `test(0,1,10,q)` with no `@` ... but when I have `q` as an `m-file` , this won't work ... see what I mean ? – JAN Jun 22 '12 at 11:26

score 2 · Answer 2 · answered Jun 22 '12 at 09:40

2

Try passing @f as the argument instead of 'f', and also change the line to

X(i) = f(x(i));

The thing is that just f is not a function handle. Also there's no need to use feval in this case.

answered Jun 22 '12 at 09:40

Ansari

8,168
2
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I can't pass `@f` (assignment rules) , I need to pass only `f` , any other suggestion maybe ? thanks – JAN Jun 22 '12 at 10:09

Passing a function as an argument into another function won't compile without using quotes ''?

2 Answers2