complex numbers as function output

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Sunetra CV
Sunetra CV el 22 de Oct. de 2019
Respondida: Hari Krishna Ravuri el 7 de Nov. de 2019
The functions used to solve my ODE's using Euler's method give real values in the first iteration ; where as the function returns complex variables from the third iteration. I'm not able to figure out the reason behind this.
function file
function f =f_UP(K)
global M Cp R P z t A tda
P = (R*K(1)*K(2));
% z = (1.4888*(t^0.75)*(Cp^0.25)*(A^0.25)*(K(3)^0.25)*(K(2)^0.25)*((K(2)-tda)^0.25))
% z = 1.4888*(t^0.75)*(Cp^0.25)*(A^0.25)*(K(3)^0.25)*(K(2)^0.25)*((K(2)-tda)^0.25);
f(1) = ((-K(1))*(1.113-2.14*z +2.81*z^2-1.76*z^3+0.396*z^4+ ...
0.08694*z^5-0.0579*z^6+0.0077*z^7))-((K(3))*(0.4235+1.5*z-1.133*z^2+0.3741*z^3-...
0.04537*z^4));
f(2)= (((-1)*R*(K(2)))./(P*M*Cp))*(760.91-1608.08*(z)+2449.22*z^2-...
(2001.61*z^3)+ 904.51*z^4 -212.087*z^5+20.095*z^6);
f(3)= ((-1)/((K(1))*(K(3))))*((1.113-2.14*z+2.81*z^2-1.76*z^3+ ...
0.396*z^4+0.08694*z^5-0.0579*z^6 +0.0077*z^7));
f=f'
Main file
clear all
close all
global M Cp R A tda z t
deltt =0.1;
t_span = 0:1;
x_H2O = 0.5;
x_CO2 = 0.5;
M_CO2 = 44*(10^-3); %kg/mol
M_H2O = 18*(10^-3); %kg/mol
M = (x_CO2*M_CO2) + (x_H2O*M_H2O);
A = 3.14*(0.091)^2;
tda = 300;
R = 8.314; %m3.Pa/mol/K
cp_CO2 = 1168; %J/kg/K
cp_H2O = 2147; %J/kg/K
Cp = (x_CO2*cp_CO2)+(x_H2O*cp_H2O)
K(1,:) = [0.43545,800,1.2]
t = 0;
tend =10;
td = 0:tend;
or i= 1:length(td)
z = 1.4888*(td(i)^0.75)*(Cp^0.25)*(A^0.25)*(K(3)^0.25)*(K(2)^0.25)*((K(2)-tda)^0.25)
K(i+1,:)= K(i,:)' + deltt*f_UP(K(i,:))
g(i)= z
% t = t+1
end
  2 comentarios
dpb
dpb el 22 de Oct. de 2019
I'd guess z goes negative...use debugger to step through and watch what happens where to find your logic error...
Sunetra CV
Sunetra CV el 23 de Oct. de 2019
Thank You. I'll look into it.

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Respuestas (1)

Hari Krishna Ravuri
Hari Krishna Ravuri el 7 de Nov. de 2019
You may consider debugging your script using MATLAB Debugger. Please refer https://in.mathworks.com/help/matlab/debugging-code.html for more information on debugging a MATLAB script.

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