change parameter values in anonymous function

My problem is one function passing to me a Anonymous function handle, for example,

f_handle = function1(a1,a2,....) 
% Assuming f_handle = @(x,y) [a*(x+y),b*(x-y)], a and be are unknown parameters

As I only get this handle, (and I know there are two unknown parameters of a and b), now I want to change (set) the parameter values of a and b, I don't know how to do it.

b=1; a=1:10;
x = 1; y =2;
for i=1:10
    % how to passing a(i) and b in the anonymouos function
    mm{i} = f_handle(x,y);
end

Should I redefine a anonymous function or by other way?

Answer 1

[madhan ravi]

 b = 1;
 a = 1:10;
 x = 1;
 y = 2;
 mm = cell(1, 10); 
 f_handle = @(x,y,a,b) [a*(x+y),b*(x-y)];
 for ii = 1:10
     mm{ii} = f_handle(x,y,a(ii),b);
 end
 celldisp(mm)

[madhan ravi]

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

[zongxian]

I'm sorry to bother you. I read the web page, but I still confusing. Your meaning is redefine a anonymous function which contains (x,y,a,b)? Can you give me a sample? Thank you.

[madhan ravi]

 b = 1;
 a = 1:10;
 x = 1;
 y = 2;
 mm = cell(1, 10); 
 f_handle = @(x,y,a,b) [a*(x+y),b*(x-y)];
 for ii = 1:10
     mm{ii} = f_handle(x,y,a(ii),b);
 end
 celldisp(mm)

[zongxian]

Maybe I didn’t make it clear, I only know f_handle (other funciton pass to me, it is not a fixed form, only know that there are two unknown parameters of a and b), now I set values for a and b, then calculation based on this f_handle, but your codes rewrite the f_handle (I think it should be auto redefine).

[madhan ravi]

 doc matlabFunction % I can’t help further  you are making a simple thing really hard to understand

[zongxian]

@madhan ravi thank you.

[madhan ravi]

 n = 1; % predefined
 f = @(x) x^n
 F = func2str(f);
 str = regexprep(F,'.*\)','');
 SYM = str2sym(str);
 "Input in the order of" + char(symvar(SYM))
 F_handle = matlabFunction(SYM)
 F_handle(2,3) % 2 assigned to n

[zongxian]

I also tried to convert it to a string, and then to an anonymous function, but it was not successful. Your way is good, but there is a problem that all variables change to input variables.

for example:

m=1;n=2;
f = @(x) x^n+m    ===>    

f= @(m,n,x)m+x.^n

If I just want to add a parameter? other parameter sill keep its values

m=1;n=2;
f = @(x) x^n+m    ===>    

m=1;
f= @(n,x)m+x.^n

Anyway, I think your method has helped me a lot.

[madhan ravi]

 n = 1;
 m = 2;
 save m
 f = @(x) x^n+m
 F = func2str(f);
 str = regexprep(F,'.*\)','');
 SYM = str2sym(str);
 syms(symvar(SYM))
 clear m
 load m
 subs(subs(SYM, {x,n},{2,3}))

Answer 2

[Steven Lord]

Once you've created an anonymous function handle that "remembers" a particular value, you cannot change that "remembered" value. You would need to recreate the function handle to change it.

n = 2;
f = @(x) x.^n; % n is locked into the value 2 at this point
y1 = f(3) % 9

n = 4;
y2 = f(3) % still 9 not 3^4 = 81

f = @(x) x.^n; % Recreating f "remembers" the new value of n
y3 = f(3) % 81

If you have a value that you want to be able to change, you should probably have the anonymous function accept it. You could, if you need a function with a specific signature, write an adapter. In the example below g accepts both x and n, while f2 and f3 fix specific values for n but make use of g to compute their results.

g = @(x, n) x.^n;
f2 = @(x) g(x, 2);
f3 = @(x) g(x, 3);

[zongxian]

If we have a anonymous function handle like your exmple (n =3; f = @(x) x.^n;), then we can not change the value of n in this handle. We can only redefine anonymous function handle after a predetermined value of n, (i.e. n = 4; f = @(x) x.^n;). Thank you.

[madhan ravi]

Not true. See https://www.mathworks.com/matlabcentral/answers/564617-change-parameter-values-in-anonymous-function#comment_936908

[Steven Lord]

In your comment you defined a new function handle F_handle. You didn't modify the existing function handle f.

[madhan ravi]

Right. I misread OPs comment. What I meant by that was there’s an alternative to overcome that problem.