Newton-Raphson Method Error

I have created a function to do Newton-Raphson method on a gas law problem. Supposedly, you enter pressure, temperature, and receive the specific volume as a result. Unfortunately, I only seem to be receiving one of my constants as the output. I can't seem to find where I went wrong. Any help?

function result=MyNewtonFn(p,t)
a=0.1747;
b=0.00138;
r=0.29681;
l(1)=1;

      function u=fun(x)
          u=(p+a./x.^2).*(x-b)/(r*t);
      end

      function w=der(q)
          w= (p + a./q.^2)/(r*t) + (2*a.*(b - q))/(r*t.*q^3);
      end

      for v=1:1000
          l(v+1)=l(v)-(fun(l(v))/(der(l(v))));
          err(v)=abs((l(v+1)-l(v))/(l(v)));
      if err(v)<=0.01
          break
      end
      end

result=l(v+1)

end

Answer 1

[Meysam Mahooti]

https://www.mathworks.com/matlabcentral/fileexchange/73563-newton-raphson-method