MATLAB: Running a While Loop and Not Getting a Different Answer

newton raphsonsolvingsystems of equations

Hello All,
I am attempting to code the Vectorial Newton Raphson Method to solve a system of equations and my code does not seem to be working. Rather, after running 100 iterations of the code I am merely getting my input back as the answer.
Here is the code:
        function[xfinal,yfinal]=NewtonVectorial(x, y, d1, d2, R, H, tol, maxiter)
        xR=x;
        yR=y;
        iter=0;
        while(1)
        xold=xR;
        yold=yR;
        new=[xold;yold]-([-sin(xold)-sin(xold+yold),-     sin(xold+yold);cos(xold)+cos(xold+yold),cos(xold+yold)])\([d1.*cos(xold)+d2.*cos(xold+yold)-R;d1.*sin(xold)+d2.*sin(xold+yold)-H])
        iter=iter+1;
        if abs(new-[xold;yold])<tol
            break
        end
        if iter>maxiter
            break
        end
        xold=new(1,1);
        yold=new(2,1);
        end
        xold
        yold
        iter
I have hard coded my partial derivatives for my Jacobian as well as the two functions I am trying to solve.
As an example for the output, this is what I am getting:
>> NewtonVectorial(pi/2,pi/4,1,1,1,1.1,.01,100)
xold =
    1.5708
yold =
    0.7854
iter =
   101
Where yold and xold are just the numbers I initially put into the code.
Any insight as to why my code is not yielding correct values would be greatly appreciated.
Thanks.

Best Answer

Drake - the problem is that the xold and yold are always being reset to x and y in the first two lines of the while loop
 while(1)
    xold=xR;
    yold=yR;
Just move these two lines outside of the loop, getting rid of xR and yR as
 xold=x;
 yold=y;
 iter=0;
 while(1)
     new=[xold;yold]- ...
     % etc.
 end
and try running your code again.
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