# How to use a fzero function and subfunctions?

1 visualizzazione (ultimi 30 giorni)
Stasha il 3 Dic 2013
Commentato: Stasha il 3 Dic 2013
Hi,
I am working on a code that involves using an fzero function but I can't figure out how to make it work. I need to find the density of air. This is what I have thus far.
%Parameters
T=250; Tb=340; Bstr=20.5*10^6; b_4=-0.00168785; b_3=-0.0223299;
b_2=-0.1704; b_1=-1.94783; b0=2.16059; b1=-0.0222243; c_3=2.50287;
c_2=-5.52109; c_1=4.29631; c0=1.19665; R=8.314; P=0.01;
tau=T/Tb;
B=Bstr*(b_4*tau^-4+b_3*tau^-3+b_2*tau^-2+b_1*tau^-1+b0*tau^0+b1*tau^1);
C=Bstr^2*(c_3*tau^-3+c_2*tau^-2+c_1*tau^-1+c0*tau^0);
x0=(initalguess);
x=fzero(@func1,x0);
p=0.029*pbar;
##### 5 CommentiMostra 4 commenti meno recentiNascondi 4 commenti meno recenti
Matt J il 3 Dic 2013
This button.
It is on the toolbar in every Question/Answer/Comment box.

Accedi per commentare.

### Risposta accettata

Stasha il 3 Dic 2013
Modificato: Matt J il 3 Dic 2013
%Inputs
%T = Temperature, P = Pressure
T = input('Required temperature in Kelvin')
P = input('Required pressure in MPa')
%Parameters
Tb=340; Bstr=20.5*10^6; b_4=-0.00168785; b_3=-0.0223299;
b_2=-0.1704; b_1=-1.94783; b0=2.16059; b1=-0.0222243; c_3=2.50287;
c_2=-5.52109; c_1=4.29631; c0=1.19665;
%Equation 2
tau=T/Tb;
B=Bstr*(b_4*tau^-4+b_3*tau^-3+b_2*tau^-2+b_1*tau^-1+b0*tau^0+b1*tau^1);
C=Bstr^2*(c_3*tau^-3+c_2*tau^-2+c_1*tau^-1+c0*tau^0);
x0=1;
x=fzero(@(pbar) 1+B*pbar+C*pbar^2,x0)
p=0.029*pbar;
%Parameters
Ts=132.5; pstr=314.3; H=6.1609*10^-6; A1=1.128516; A_5=2.60661; A0=-1.00;
A_1=-0.709661; A_2=0.662534; A_3=-0.197846; A_4=0.00770147; B1=0.465601;
B2=1.26469; B3=-0.511425; B4=0.2746;
%Equation 1
pr=p/pstr;
Tr=T/Ts;
yt=A1*Tr+A_5*Tr^0.5+A0*Tr^0+A_1*Tr^-1+A_2*Tr^-2+A_3*Tr^-3+A_4*Tr^-4;
yp=B1*pr+B2*pr^2+B3*pr^3+B4*pr^4;
y=H*(yt+yp);
end
%subfunction
function [] = pbar
% Parameters
T=250; R=8.314;
Z=P/pbar*R*T;
Z=1+B*pbar+C*pbar^2
end
##### 0 CommentiMostra -1 commenti meno recentiNascondi -1 commenti meno recenti

Accedi per commentare.

### Più risposte (1)

sixwwwwww il 3 Dic 2013
Your code is working but its not giving correct ans because of your initial condition:
%Parameters
T=250;
Tb=340;
Bstr=20.5*10^6;
b_4=-0.00168785;
b_3=-0.0223299;
b_2=-0.1704;
b_1=-1.94783;
b0=2.16059;
b1=-0.0222243;
c_3=2.50287;
c_2=-5.52109;
c_1=4.29631;
c0=1.19665;
%Equation 2
tau=T/Tb;
B=Bstr*(b_4*tau^-4+b_3*tau^-3+b_2*tau^-2+b_1*tau^-1+b0*tau^0+b1*tau^1);
C=Bstr^2*(c_3*tau^-3+c_2*tau^-2+c_1*tau^-1+c0*tau^0);
x0 = 1;
x = fzero(@(pbar)1+B*pbar+C*pbar^2 ,x0) ;
##### 1 CommentoMostra NessunoNascondi Nessuno
Stasha il 3 Dic 2013
Sixwwwwww, The code you said runs fine is not my complete code. The one above it is and that is the one I'm getting an error on.

Accedi per commentare.

### Categorie

Scopri di più su Acoustics, Noise and Vibration in Help Center e File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by