the code doesn't update the values

anyone can help with this matlab code it doesn't update the values of p and t

n=1
while n<20
 p=10^((30.59051-8.2*log10(t))+(0.0024804*t)-(3142.31/t))
 t=314+((6.324-p)/(6.66*(10^-4)*101.32));
 n=n+1;
end

Answer 1

[dpb]

Of course it does, it just doesn't do what you think it should, apparently...

ADDENDUM-

If you're also expecting to build vectors of t and p, then you need to tell Matlab that, too...

Several problems here...

• First, t is undefined at the beginning of the loop

What is it to be to begin with. If you start w/ t=0, then

log10(0)-->-Inf

and you divide by it later on, too. Solve those issues and you'll at least get some numeric output.

Before the loop add

p=zeros(20,1); t=p;   % preallocate

Inside the loop then

p=...

needs must become

p(n)=...;

and likewise for t to save the individual values.

[ibrahim]

i started with t=300

[dpb]

Your equations are very unstable--in particular t oscillates wildly and then essentially "blows up". Observe first few iterations...

>> t=300;p=0;
>>  n=1; disp([n t p])
while n<6 
p=10^((30.59051-8.2*log10(t))+(0.0024804*t)-(3142.31/t));
t=314+((6.324-p)/(6.66*(10^-4)*101.32));
n=n+1; 
disp([n t p])
end
   1   300     0
  2.0000  355.3940    3.5308
  3.0000 -360.1268   51.8135
 1.0e+18 *
 0.0000            -3.4568 + 2.5115i   0.2333 - 0.1695i
  5.0000  407.7179         0
 1.0e+03 *
  0.0060   -4.1697    0.3089
>>

This isn't a Matlab problem; it's in the equations as written...

[ibrahim]

thank you

[dpb]

So what are the equations intended to represent and where did you obtain them? Looks like a correlation of some sort; are you sure you've coded them correctly and are using proper units to scale t,p initial values within defined range of the correlation is so?

Answer 2

[Azzi Abdelmalek]

You need to initialize your variable t