solve nonlinear equation

2011 5 31
3 个回答
4 次查看（30 天）

0 个投票

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

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回答（3 个）

Oleg Komarov
Oleg Komarov 2011-5-31

0 个投票

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)

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Walter Roberson
Walter Roberson 2011-6-1
- 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
Oleg Komarov 2011-6-1
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)
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
Matt Fig 2011-6-1
Read the rest of the post. FUNC2STR is working just like Oleg showed...

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Walter Roberson
Walter Roberson 2011-6-1

0 个投票

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.

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Oleg Komarov
Oleg Komarov 2011-6-1
Totally agree
unfourtanetly, I must use handle function
Walter Roberson
Walter Roberson 2011-6-1
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
Walter Roberson 2011-6-1
If the assignment prohibits you from passing around symbolic variables, then why does it permit you to use solve(), the symbolic equation solver?

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0 个投票

I'm still have the same problem

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Oleg Komarov
Oleg Komarov 2011-6-1
What do you mean you have the same problem? Post the whole code you're using and the error message.

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