while loop running forever during attempt at Newton Rhapson method

This code keeps running seemingly forever, or at least a few minutes. I can't figure out why, could someone please explain what is going wrong? unless i wrote the actual functions of d wrong it should be expected to converge towards something until the while loop condition isn't fullfilled anymore

d=0.007;
dI=1.219;
Rfi=1.76*(10^(-4));
Rf0=Rfi;
hs=356;
ht=hs;
kw=60;
dTm=29.6;
Q=801368;
Aex=64.15;

a=((1/ht)+Rfi)/dI;
b=log(d/dI)/2*kw;
c=d*(a+b)+Rf0+(1/hs);

f=(c^(-1))-Q/(Aex*dTm);

df=-1*(c^(-2))*(a+b)*(dI/(d*2*kw))*(1/dI);

%d1-do ska va mindre än tol
%i slutet av iterationen
%så man kan sätta while

d=0.007;
d0=d;
d1=10;
abs(d1-d0);
while abs(d1-d0)>10^(-8);
    d0=d;
    d1=d0-f/df;
    d=d1;
end
d1

Answer 1

[VBBV]

d=0.007;
dI=1.219;
Rfi=1.76*(10^(-4));
Rf0=Rfi;
hs=356;
ht=hs;
kw=60;
dTm=29.6;
Q=801368;
Aex=64.15;
a=((1/ht)+Rfi)/dI;



%d1-do ska va mindre än tol
%i slutet av iterationen
%så man kan sätta while

d=0.007;
d0=d;
d1=10;
abs(d1-d0);
while abs(d1-d0)>10^(-8);
    
    b=log(d/dI)/(2*kw);
    c=d*(a+b)+Rf0+(1/hs);
    
    f=(c^(-1))-Q/(Aex*dTm);
    
    df=-1*(c^(-2))*(a+b)*(dI/(d*2*kw))*(1/dI);
    d0=d;
    d1=d0-f/df;
    d=d1;
end
d1

d1 = 0.0191

[VBBV]

Place the lines of coe inside the while loop which are function of variables d and expression for evaluating d1 inside the while loop

b=log(d/dI)/(2*kw);
c=d*(a+b)+Rf0+(1/hs);
f=(c^(-1))-Q/(Aex*dTm);
df=-1*(c^(-2))*(a+b)*(dI/(d*2*kw))*(1/dI);

[Torsten]

@VBBV

Are you sure it must read

b=log(d/dI)/(2*kw);

instead of

b=log(d/dI)/2*kw;

as in the original code ?

Answer 2

[Torsten]

Your function doesn't seem to have a zero.

d=0.007;
dI=1.219;
Rfi=1.76*(10^(-4));
Rf0=Rfi;
hs=356;
ht=hs;
kw=60;
dTm=29.6;
Q=801368;
Aex=64.15;

a=((1/ht)+Rfi)/dI;
b=@(d)log(d/dI)/2*kw;
c=@(d)d.*(a+b(d))+Rf0+(1/hs);

f=@(d)(c(d).^(-1))-Q/(Aex*dTm);
D = 0.1:0.01:10;
plot(D,f(D))

df=@(d)-1*(c(d)^(-2))*(a+b(d))*(dI/(d*2*kw))*(1/dI);

%d1-do ska va mindre än tol
%i slutet av iterationen
%så man kan sätta while

d=0.007;
d0=d;
d1=10;
abs(d1-d0);
while abs(d1-d0)>10^(-8);
    d0=d;
    %df0 = (f(d0+1e-7)-f(d0))*1e7
    d1=d0-f(d0)/df(d0);
   % d1 = d0-f(d0)/df0;
    d=d1
end

d = 2.6870

d = -2.3299e+07

d = 3.2216e+29 + 6.0366e+28i

d = -3.0746e+96 - 1.9209e+96i

d = -1.4912e+297 +1.6013e+298i

d = Inf + Infi

d = NaN + NaNi

d1

d1 = NaN + NaNi