Problem with my Code?

[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

Answer 1

[Paulo Silva]

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.

[Cote]

okay so completely get rid of the newton() parts?

[Paulo Silva]

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]

Wait sorry how can I save the function to the current path and use it with the script?

[Paulo Silva]

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]

So if my function is saved as Newton.m then I open a new file and use my script in there?

[Paulo Silva]

yes

[Cote]

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]

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]

isn't this the same as before?

[Paulo Silva]

there were problems resulting in the error "unbalanced or unexpected parenthesis or bracket", works fine with that last code.

[Cote]

So do I just use this in the editor right after the function x = Newton(f, fp, x, nmax, error) part

[Paulo Silva]

replace all the script that calls the function with the corrected one I posted, keep the function file the same.

[Cote]

when I run the script and function together i get Error in ==> iscellstr whatever that means

[Walter Roberson]

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]

Nevermind I got it to work thanks for all your help!

[Cote]

And that thank you is directed towards Paulo and Matt

Answer 2

[Matt Tearle]

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.

[Matt Tearle]

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]

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]

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]

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]

okay thank you