iam trying to input two equations throw edit text in matlab gui and i want to know what is the error (iam solving by newton's method for non-linear equations)

syms x y

f1=get(handles.f1,'string');

fn1=inline(f1); 

f2=get(handles.f2,'string');

fn2=inline(f2); 

g1=get(handles.g1,'string');

g2=get(handles.g2,'string');

n=get(handles.n,'string');

g1=str2double(g1);

g2=str2double(g2);

n=str2double(n);

xo =[g1;g2];

h=[fn1;fn2];

   g=[diff(fn1,x) diff(fn1,y);diff(fn2,x) diff(fn2,y)]; 

j=inv(g);

for i=1:n

f= double(subs(h,{x,y},{[xo(1)],[xo(2)]}));

j= double(subs(g,{x,y},{[xo(1)],[xo(2)]}));

   xn=xo-j*f;

   xo=xn;

   out=xn;

end

out=num2str(out);

set(handles.out,'string',out)

[Geoff Hayes]

abdelaziz - are you observing an error with the above code, and if so, what is it? Please clarify your question.

By the way, without knowing what your controls represent (i.e. f1, f2, g1, g2, n) if they are numbers then I expect that you will need to convert them from strings to numbers. Something like

 n=str2num(char(get(handles.n,'string')));

And the reverse when going the other way if out is a number (or maybe it is an expression?)

 set(handles.out,'string',num2str(out))

[abdelaziz abdelaziz]

f1 and f2 are input equations for g1;g2 is matrix 2*1 for initial guess n is number of iterations the error appeared is ( xn=xo-j*f;) he said Matrix dimensions must agree.

[Geoff Hayes]

Please clarify what you mean by he said Matrix dimensions must agree. Which line of your code does this error message correspond to? Typically it means that you are trying to do some sort of operation (addition, subtraction, multiplication, etc.) between two matrices that have incompatible dimensions for the operation..

[abdelaziz abdelaziz]

the error says : inline function cant be concatenated and also there is error

h=[fn1;fn2];

i dont now what is meant by that errors

Answer 1

[Walter Roberson]

You need to use double() on the symbolic numbers, such as

f = double(subs(h,{x,y},{[xo(1)],[xo(2)]}));

[Walter Roberson]

Do not use inline functions. For example, recode

fn1=inline(f1);

to

fn1 = matlabFunction(sym(f1));

or

fn1t = str2func(['@(x) ' fn]);  %generate anonymous function
fn1 = fn1t(x);     %apply it at the symbol x

Which one you use will depend upon whether the expression provided by the user is going to be in symbolic toolbox notation or in MATLAB notation. For example for x+x^2+x^3 can the user write

sum(x^n,n=1..3)

which is symbolic notation, or would they write

sum(x.^(1:n))

which is MATLAB notation.