need mfile for my non linear system

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hasan s 2020-12-24

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评论： Walter Roberson 2021-1-22

I have to employ the newton raphson algorithm to solve my equations,. I need to create a function m-file to do so. This is my first matlab assignment and I'm not really familiar with it. I don't really know how to go about the iteration and I try to write it but matlab not solve. this is my try. Any help would be greatly appreciated.

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hasan s 2021-1-22

It has been discovered that the question I asked contains errors

The program has been canceled due to a mistake in the question

I deleted it so as not to affect the followers because my question is wrong

Your valuable suggestions remain.

Thanks for your efforts

Walter Roberson 2021-1-22

However, our solution is for the question as posted, and is useful for people who might want to study the techniques.

It is not uncommon for people to discover that they made a mistake in asking the question when they start thinking about the responses they got. It is also not uncommon that when users see how the volunteers interpret the question that was actually asked, that the user's thought processes are pulled out of the grove they were in, and are able to see how they should have proceeded. Thus, even questions containing mistakes are valuable to readers. Indeed, most questions that are posted contain a mistake of some sort, and figuring out what the mistake is is a lot of what we do here.

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Answer 1

Cris LaPierre 2020-12-24

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https://ww2.mathworks.cn/matlabcentral/answers/701952-need-mfile-for-my-non-linear-system#answer_583932

You can find examples and explanations about how to create a funciton file here:

https://www.mathworks.com/help/matlab/matlab_prog/create-functions-in-files.html

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Walter Roberson 2020-12-25

在 MATLAB Online 中打开

Your file name has a space in it. Untitled 33.m . You need to remove the space.

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;(G(i)^2)*(gamma(1+2/A(i))) 
+(2*B(i)*G(i)*gamma(1+1/A(i)) 
+B(i)^2-sum2);(G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)]; 

MATLAB does not continue lines automatically (unlike C, for example).

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;(G(i)^2)*(gamma(1+2/A(i)))
    1 0  1 0 1     2     3 320

so the part up to the ; is a valid complete element, and the ; explicitly marks the end of a row

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;(G(i)^2)*(gamma(1+2/A(i)))
                                    1 2 1  0 1     2     3 210

so the (G to end of line is a valid complete element. Inside [], when a line ends with no continuation symbol, that is treated as an implicit end of row, as if you had written a ; at the end of the line. Thus, the above line of code gives two complete matrix rows.

 +(2*B(i)*G(i)*gamma(1+1/A(i)) 
  1   2 1  2 1      2     3 21      <== missing )

You are inside [] so MATLAB will try to treat that as a matrix row. However, it is missing a ) to be a valid matrix row. The + at the beginning of the line is not a problem: it is treated as a "unary plus". Just the same way that you can write -5 to indicate 0 minus 5, or -x to indicate 0 minus x, you can write +5 to indicate 0 plus 5, or +x to indicate 0 plus x. In this context, the + does not signal that you are in the middle of an addition.

+B(i)^2-sum2);(G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)]; 
  1 0       !

Again, the + at the beginning of the line is valid unary operation and does not signal that you are in the middle of an addition. But then you have one extra ) on the matrix element.

What you probably wanted was

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;(G(i)^2)*(gamma(1+2/A(i)))... 
+(2*B(i)*G(i)*gamma(1+1/A(i))...
+B(i)^2-sum2);(G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)];

which in turn would be better written

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;
   (G(i)^2)*(gamma(1+2/A(i)))+(2*B(i)*G(i)*gamma(1+1/A(i))+B(i)^2-sum2);
   (G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)];

We are not able to test the code as you did not initialize T or G or B or A.

Also

Program (2)

You should probably be storing the second program in its own file.

Walter Roberson 2020-12-31

在 MATLAB Online 中打开

I did not write gamma "instead" of anything. Your code had

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;(G(i)^2)*(gamma(1+2/A(i))) 
+(2*B(i)*G(i)*gamma(1+1/A(i)) 
+B(i)^2-sum2);(G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)]; 

which already has gamma in it. I reformatted,

x=[B(i)+G(i)*(gamma(1+1/A(i)))-sum1;
    (G(i)^2)*(gamma(1+2/A(i)))+(2*B(i)*G(i)*gamma(1+1/A(i))+B(i)^2-sum2);
    (G(i)^3*gamma(1+3/A(i))+3*B(i)*G(i)^2*gamma(1+2/A(i))+3*G(i)*B(i)^2*gamma(1+1/A(i))+B(i)^3-sum3)]; 

which is just moving around the line breaks.

q=inv(d); 
p=q*x;

cannot be replaced by x/d but can be replaced by

p=d\x;

No,

A(i+1)=z; 
B(i+1)=z; 
G(i+1)=z; 

is not a replacement for the existing lines. z is a vector of length 3, but A(i+1) only designates a single output location. You also want A, B, and G to get different outputs, but assigning z to all of them would give the same value to each.

What you could do is

zcell = num2cell(z(1:3));
[A(i+1), B(i+1), G(i+1)] = zcell{:};

but this is less clear than just doing three assignment statements.

T=1;
A=2;
B=3;
G=4;

That will not work. You have

for j=1:50 
sum1=sum1+log((T(j)-B(i))/G(i)); 

When j becomes 2, you need to access T(2) but T has only been initialized as a scalar. You never store into T after the initial assignment.

hasan s 2021-1-6

THANK YOU VERY MUCH

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