solve nonlinear equation

I write a method to solve any equation

function [ result ] = get( func )
%UNTITLED2 Summary of this function goes here
%   Detailed explanation goes here
result=solve(func);
end

when I run it on command window,I get an error.

 >> f=@(x) 2*x+1

 f = 

    @(x)2*x+1
>> [ result ] = get( f )
??? Error using ==> error
Function is not defined for 'function_handle' inputs.

 Error in ==> solve>getEqns at 182
           error('symbolic:solve:errmsg1', ...

 Error in ==> solve at 67
 [eqns,vars] = getEqns(varargin{:});

 Error in ==> get at 4
 result=solve(func);

so how can I fix the error

Answer 1

[Oleg Komarov]

You cannot solve a function handle.

You have to convert the anonymous function handle to a string function:

fh = @(x,y) 2*x+1-2*y;

% Convert to string
fs = func2str(fh);

% Extract only function part w/o @(.)
fs = regexprep(fs,'@\([\w,]+\)','');

% Solve
solve(fs)

[Walter Roberson]

- Be careful about which variable is being solved for

- func2str() only going to do a literal string conversion. If any of the variables involved have "captured values", then the captured value will not have its value substituted by func2str()

- searching for the first ')' and deleting from the beginning to there would probably be more efficient than regexprep()

[Oleg Komarov]

The snippet is just un unrefined example, thus point 1 wasn't addressed in the example explicitly.

For point 2 I agree it becomes overly complicated (functions, workspace...) for a problem that can be stated as symbolic from the beginning

For point 3 premature optimization is the... :D (just wanted to write a one liner)

[Eman Ahmed Elsayed]

func2str doesn't work with me

>> f=@(x) 2*x+1

f =

@(x)2*x+1

>> func2str(f)

ans =

@(x)2*x+1

It's return the same equation

[Matt Fig]

Read the rest of the post. FUNC2STR is working just like Oleg showed...

Answer 2

[Walter Roberson]

solve() only applies to symbolic expressions. If you are going to use symbolic expressions you might as well do so from the start and save the trouble about constructing function handles.

[Oleg Komarov]

Totally agree

[Eman Ahmed Elsayed]

unfourtanetly, I must use handle function

[Walter Roberson]

If this is for an assignment, then it would help us to read the assignment question, as then we would not suggest things you cannot use.

[Walter Roberson]

If the assignment prohibits you from passing around symbolic variables, then why does it permit you to use solve(), the symbolic equation solver?

Answer 3

[Eman Ahmed Elsayed]

I'm still have the same problem

[Oleg Komarov]

What do you mean you have the same problem? Post the whole code you're using and the error message.