Passing the input to another function

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Hi everyone,

I'm trying to write a function for solving 1st order ODEs: dy/dx=f(x,y(x)) using taylor methode and I want it in a seperate file than the file where the user inputs the function:

here's the main program:

clear all
syms x y
f=input('fct')
g=inline(f)
yi=taylor(g,3,5,0,1,0.1)

here's the taylor fct:

function yi=taylor(f,o,np,x0,y0,h)
% o is order
% np is number of points
% x0 is the 1st point
% y0 is the value of the solution in x0 (initial condition)
% h is the step
        xi=x0:h:x0+np*h
        format long 
        syms x y 
        
        F=symfun(f,[x y]) %here is the problem
        
        dF(1)=F;
        for i=2:o
            dF(i)=diff(dF(i-1),x)+dF(1)*diff(dF(i-1),y);
        end
        df=matlabFunction(symfun(dF,[x y]));
        yi(1)=y0;
        for i=1:np
            d=df(xi(i),yi(i));
            r=0;
            for j=1:o
                r=r+((h^j)/factorial(j))*d(j);
            end
            yi(i+1)=yi(i)+r;
        end
end

my problem is that it wouldn't let me convert the f that i have just input to symbolic, so I want to know how to pass a function that was introduced by the user to another one and use symbolic functions in it (i.e: diff)

Thank you