Problem with my Code?

2011 4 18
2 个回答
回答已采纳
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0 个投票

[EDIT: 20110512 17:03 EDT - reformat - WDR]
I keep getting the error Undefined function or method 'Newton' for input arguments of type 'inline'. I'm doing newtons method and I can't figure out what that error means and what part of my code is wrong.
function x = Newton(f, fp, x, nmax, error)
x=1;
e=2.71828;
f(x)=inline('(x)*(5000)*(e^(-x)))-((100)+(0.73)*(5000)*(e^(-x))');
fp(x)=inline('-5000*(e^(-x))*(x-1.73)');
nmax = 10;
error = 1.0e-15;
x = Newton(f,fp,x,nmax,error)
fprintf('x(0) = %10g \n', x)
for n = 1:nmax
d = f(x)/fp(x);
x = x - d;
fprintf('x(%i) = %10g \n', n, x)
if abs(d) < error
fprintf('Converged! \n')
return
end
end
end

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 采纳的回答

Paulo Silva
Paulo Silva 2011-4-18

0 个投票

There's no Newton function on MATLAB current path or any other path that MATLAB is aware, you get the same error for
whateverfunctionisayso(inline('x'))
This should be your script:
x=1;
f=inline('x*5000*exp(-x)-(100+0.73*5000*exp(-x))');
fp=inline('-5000*exp(-x)*(x-1.73)');
nmax = 10;
error = 1.0e-15;
x = Newton(f,fp,x,nmax,error)
fprintf('x(0) = %10g \n', x)
And this is your function:
function x = Newton(f, fp, x, nmax, error)
for n = 1:nmax
d = f(x)/fp(x);
x = x - d;
fprintf('x(%i) = %10g \n', n, x)
if abs(d) < error
fprintf('Converged! \n')
return
end
end
end
Save the function to the current path or another that MATLAB is aware of and run the script.

16 个评论
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Cote
Cote 2011-4-18
okay so completely get rid of the newton() parts?
Paulo Silva
Paulo Silva 2011-4-18
you are confused with the script that calls the function and the function
SCRIPT
x=1;
e=2.71828;
f(x)=inline('(x)*(5000)*(e^(-x)))-((100)+(0.73)*(5000)*(e^(-x))');
fp(x)=inline('-5000*(e^(-x))*(x-1.73)');
nmax = 10;
error = 1.0e-15;
x = Newton(f,fp,x,nmax,error)
fprintf('x(0) = %10g \n', x)
FUNCTION
function x = Newton(f, fp, x, nmax, error)
for n = 1:nmax
d = f(x)/fp(x);
x = x - d;
fprintf('x(%i) = %10g \n', n, x)
if abs(d) < error
fprintf('Converged! \n')
return
end
end
end
Cote
Cote 2011-4-19
Wait sorry how can I save the function to the current path and use it with the script?
Paulo Silva
Paulo Silva 2011-4-19
just press the save button from the editor, the m file name should be the same as the function name and the folder (that opens first) is the current path, press save.
Cote
Cote 2011-4-19
So if my function is saved as Newton.m then I open a new file and use my script in there?
Cote
Cote 2011-4-19
I can't get this to work, not quite sure what I'm doing wrong but I still think it has something to do with the way I'm saving the files and its directory
Paulo Silva
Paulo Silva 2011-4-19
Use this script instead
x=1;
f=inline('x*5000*exp(-x)-(100+0.73*5000*exp(-x))');
fp=inline('-5000*exp(-x)*(x-1.73)');
nmax = 10;
error = 1.0e-15;
x = Newton(f,fp,x,nmax,error)
fprintf('x(0) = %10g \n', x)
Cote
Cote 2011-4-19
isn't this the same as before?
Paulo Silva
Paulo Silva 2011-4-19
there were problems resulting in the error "unbalanced or unexpected parenthesis or bracket", works fine with that last code.
Cote
Cote 2011-4-19
So do I just use this in the editor right after the function x = Newton(f, fp, x, nmax, error) part
Paulo Silva
Paulo Silva 2011-4-19
replace all the script that calls the function with the corrected one I posted, keep the function file the same.
Cote
Cote 2011-4-19
when I run the script and function together i get Error in ==> iscellstr whatever that means
Walter Roberson
Walter Roberson 2011-4-19
Exactly which line does it say that the problem is occurring at? When you put a breakpoint at that line and run again, what values do you see for the variables of that routine? When you go downwards in the call stack to find your routine, which line of the routine is it indicating invoked the problem? When you put a breakpoint at that line, then what values are you passing in to the call you see there? What happens when you delete all of your previous MATLAB Questions without even thanking the people who assisted you in solving your problem?
Cote
Cote 2011-4-19
Nevermind I got it to work thanks for all your help!
Cote
Cote 2011-4-19
And that thank you is directed towards Paulo and Matt

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更多回答（1 个）

Matt Tearle
Matt Tearle 2011-4-18

0 个投票

That message generally means that your function file isn't on the MATLAB path. Is Newton.m in your current directory?
There are some other issues with your code, but they wouldn't cause that error.

5 个评论
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Matt Tearle
Matt Tearle 2011-4-18
Looks like Paulo figured out what you were trying to do. So I'll just add that function handles are preferable to inline, and, either way, use y = exp(x) instead of e = 2.71828; y = e^x
Cote
Cote 2011-4-18
Thanks for the suggestion and that would mean I just need to change all of my e's to y's after setting y = exp(x) correct?
Paulo Silva
Paulo Silva 2011-4-19
exp(1) equals to your e variable, that is 2.718281828459046
on the inline expressions use exp instead of the e variable
f(x)=inline('(x)*(5000)*(exp(-x)))-((100)+(0.73)*(5000)*(exp(-x))');
fp(x)=inline('-5000*(exp(-x))*(x-1.73)');
Paulo Silva
Paulo Silva 2011-4-19
Matt is also right about using function handles instead of inline expressions but I wouldn't bother much with it, all should work good with your current code.
Cote
Cote 2011-4-19
okay thank you

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