Problem Help!

Here are my codes, I keep getting wrong feedback which drive me crazy! Here's the problem: Basicly the problem is to solve a nonlinear equation by using the fzero command. The function is Φ（r)=[Φ0*e^-r/delta]/(4*pi*D*r) And solve r when Φ（r)/Φ0=10% Every parameters are in the command

My problem is: Index exceeds matrix dimensions.

Error in YZHW61 (line 47) fprintf(' %6.3f %2u %6.2f %+6.2E \n',...

%%YZHW61
%Find the distance away from the point source of laser
%
%Written 2/11/2012 by YZ
%Last updated 2/11/2012 by YZ
%
%First list parameters
%μs’=μs（1-g)=10cm-1
%μt’=μa+μs’=10.1cm-1
%D=（1/3）*μt’=3.37cm-1
%δ=sqrt（D/μa）=5.8
%So the final equation becomes Φ(r)=(Φ0*e^(-r/5.8))/(4*pi*3.37*r)
%Simplify the equation and we get:
%Φ=(e^(-r/5.8))/13.48*pi*r where Φ(Phi)=Φ(r)/Φ0 that represents the
%percentage of the new light intensity compared to the original 
%light intensity
date
clear all
%First plot Diffusion Equation for r between 0.5 and 100
for i=1:1:200; %loop counters musht be be nonzero,positive integers
    r=i/2; %this will give us 0.5cm distance
    press(i)=r;
    g=0.9;
    mius=100;
    miua=0.1;
    mius1=mius*(1-g);
    miut1=miua+mius1;
    D=(1/3)*miut1;
    delta=sqrt(D/miua);
    P(i)=exp(-r/delta)/(4*pi*D*r)*100;
end
hold on
plot(press,P);axis equal; grid
%
% Get user input for the light fluence rate(percentage)
%We need to pass this information to the function by using the global
%variable
global Phi
Phi=0.1;
%
%Choose initial guess
distance=1;
[r,error,exitflag,output]=fzero(@Diffusion,distance);
%
%What's the solution, how many iterations, what's the error?
fprintf=('distance  (Iterations   fluence rate   error)  \n');
fprintf('  %6.3f      %2u           %6.2f     %+6.2E    \n',...
    r, output.funcCount, Phi, error)
plot(r,0.1,'o')

And here is my function:

function Pest=Diffusion(distance)
%Diffusion equation for distance r
%
%First written by YZ on 2/11/2012
%Last updated by YZ on 2/11/2012
%
global Phi
    g=0.9;
    mius=100;
    miua=0.1;
    mius1=mius*(1-g);
    miut1=miua+mius1;
    D=(1/3)*miut1;
    delta=sqrt(D/miua);
    Pest=exp(-distance/delta)/(4*pi*D*distance)*100-Phi;
end

Really appreicate anyone who can help me!

[Walter Roberson]

What problem are you encountering? There is nothing in your source that an on-looker would clearly understand to be "feedback", and you have not mentioned any error message.

[Yu]

I'm so sorry, please see the edited verision.

Answer 1

[Image Analyst]

Several errors in your code. The big one is this line:

fprintf=('distance  (Iterations   fluence rate   error)  \n');

You are not allowed to have an equal sign after fprintf(). I think what you did was to essentially overwrite fprintf with a character string. Then in the next line you tried to access some element of the string beyond the end of it.

Secondly, you are overwriting error(). DON'T DO THAT! It's a built in function. Use "errorStructure" as the name instead of "error".

[r,errorStructure,exitflag,output]=fzero(@Diffusion,distance);

[Yu]

Thank you for your answer, however, I changed r from 0.005 to 1 and changed the initial guess to 0.005 due to my understand and graph to the function; but then I encountered a new problem: too many output arguments.It that because I choos the wrong initial guess? Because I changed to different values and still get the same mistake.

[Image Analyst]

I don't care at all about those. Did you change what I said to change? Did you remove the equal sign and rename error to errorStructure?

[Yu]

I did; actually the changes are made after I did what you want me to change.

[Image Analyst]

I don't see how r was ever .005. I see that it was r=i/2. Where does it now equal 1? Also, what line said that some function had too many output arguments? It helps if you paste the error.

[Yu]

Error using error

Too many output arguments.

Error in YZHW61 (line 47)

fprintf(' %6.3f %2u %6.2f %+6.2E \n',...

This is my error.

And I set r range from 0.005 to 1; because i have to be nonzero and positive figures so I let r=i/200 to get the range of r.

for i=1:1:200; %loop counters musht be be nonzero,positive integers

r=i/200; %this will give us 0.005 distance

[Image Analyst]

Doesn't make sense. You're not using "error" anymore, remember? I told you to change it to "errorStructure" and you said you did.

[Yu]

distance=0.005;

[r,errorStructure,exitflag,output]=fzero(@Diffusion,distance);

This is what I did according to your suggestion.

[Yu]

Got it, thank you so much !

[Image Analyst]

I guess you also eventually remembered to change it in the fprintf() also.