MATLAB: Undefine variable ‘t’

#undefine variable

I do not know at which point I make mistake.

function dydt = comb(t,y)
R = 8314.510; % J/kmol.K
Cp = 1200; % J/kg.K
h_F = 4e7; % J/kg
Po = 2545284; % Pa
To = 753; % K
Fo = Po/(17*R*To);
Oxo = 16*Po/(17*R*To);
Pro = 0;
dydt = [-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1)));...
     (-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1));...
     16*((-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1)));...
     -17*((-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1)))]
[t,y]= ode15s(@comb, [0 0.004],[300;Po/(17*R*To);16*Po/(17*R*To);0]);
plot(t,y(:,1),'-o');
title('Temperature vs time');
xlabel('Time, t [s]');
ylabel('Temperature, T[K]');
end

Best Answer

R = 8314.510; % J/kmol.K

Cp = 1200; % J/kg.K

h_F = 4e7; % J/kg

Po = 2545284; % Pa

To = 753; % K

Fo = Po/(17*R*To);
Oxo = 16*Po/(17*R*To);
Pro = 0;
[t,y]= ode15s(@comb, [0 0.004],[300;Po/(17*R*To);16*Po/(17*R*To);0]);   %function calling ourside the function definition
plot(t,y(:,1),'-o');
title('Temperature vs time');
xlabel('Time, t [s]');
ylabel('Temperature, T[K]');
function dydt = comb(t,y)
R = 8314.510; % J/kmol.K
Cp = 1200; % J/kg.K
h_F = 4e7; % J/kg
Po = 2545284; % Pa
To = 753; % K
Fo = Po/(17*R*To);
Oxo = 16*Po/(17*R*To);
Pro = 0;
dydt = [-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1)));...
     (-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1));...
     16*((-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1)));...
     -17*((-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))-(y(2)*(-h_F*(-6.19e9*exp(-15098/y(1))*(y(2)^0.1)*((0.21*y(3))^1.65))/(Cp*Po/(R*y(1))))/y(1)))]
end

Related Solutions

MATLAB: Solvin Differential Algebraic Equations

function main
  %gaslift systems network
  tspan = [0:1:60];
  % The script for gas lift network model defining initial conditions and
  % boundaries
  y0 =[2812.3; 1269.75; 9200.4; 136.9; 2300.2; 160; 80.52; 113.87; 127.9; 
      340.29; 428.8; 130.54; 30; 50.77; 1.853;63.65; 7.71; 55.93; 13.62; 1.36;
      205.86; 11.56; 194.3];
  M = diag([ones(1,5) zeros(1,18)]);
  options = odeset('Mass',M);
  % call 
  [t,y] = ode15s(@gas_lift_ftn,tspan,y0,options);
end
function out = gas_lift_ftn(t,y)
  %Define other parameters%
  mu_o = 0.01; 
  pi = 3.14; 
  Lw = 1500;
  Hw = 1000; 
  Dw = 0.121;
  Lbh = 500; 
  Hbh = Lbh; 
  Dbh = Dw; 
  La = Lw; 
  Ha = Hw; 
  Da = 0.189;
  Lr = Lbh;
  Hr = Lbh; 
  Dr = Dw; 
  Aw = (pi/4)*Dw^2;
  Abh = Aw;
  Ar = Aw;
  Aa = (pi/4)*Da;
  Va = La*pi/4*(Da^2-Dw^2);
  rho_o = 800;
  Civ = 0.1e-03; Crh = 10e-3; Cpc = 2e-3;
  Pr = 150; Ps = 20; PI = 0.7; 
  Ta = 28+273; Tw = 32+273; Tr = 30+273; Mw = 20; R = 0.083145;
  g = 9.8*10e-5; GOR = 0.1; wgl = 2.217;
  out=zeros(23,1);
  out(1) = wgl - y(15);
  out(2) = y(15) - y(19) + y(18);
  out(3) = y(20) - y(21);
  out(4) = y(19) - y(22);
  out(5) = y(21) - y(23);
  out(6) = ((((Ta*R)/(Va*Mw))+((g*La)/(La*Aa)))*y(1)) - y(6);
  out(7) = (Mw*y(6)) -(Ta*R*y(9));
  out(8) = (((((Tw*R)/Mw))*((y(2))/((Lw*Aw)+(Lbh*Abh)-(y(3)/rho_o)))- 0.5*((y(2)+(y(3))/(Lw*Aw))*g*Hw))-y(7));
  out(9) = y(2)+ y(3)-(rho_o*Lbh*Abh)-(Lw*Aw*y(10));
  out(10) = (y(7)+((g/(Lw*Aw))*(y(3)+y(2)-(rho_o*Lbh*Abh)*Hw))+((128*mu_o*Lw*y(16))/(pi*Dw^4*((y(2) + y(3))*y(7)*Mw*rho_o)/(y(3)*y(7)*Mw + rho_o*R*Tw*y(2)))))-y(8);
  out(11) = (y(8)+ (y(10)*g*Hbh)+((128*mu_o*Lbh*y(20))/(pi*Dbh^4*rho_o)))-y(12);
  out(12) = (Tr*R*y(4))-(Mw*Lr*Ar*y(13));
  out(13) = y(4)+ y(5)-(Lr*Ar*y(11));
  out(14) = (y(13) + y(11)*g*Hr + ((128*mu_o*Lr*y(17))/(pi*Dr^4*((y(4) + y(5))*y(13)*Mw*y(11))/(y(5)*y(13)*Mw + y(11)*R*Tr*y(4)))) - y(14));
  out(15) = (Civ*sqrt(y(9)*(y(6)-y(8))))-y(15);
  out(16) = (Cpc*sqrt(y(10)*(y(7)-y(14))))-y(16);
  out(17) = (Crh*sqrt(y(11)*(y(6)-Ps)))- y(17);
  out(18) = (PI*(Pr -y(12)))- y(20);
  out(19) = GOR* y(20) -y(18);
  out(20) = (y(2)*y(16)) - (y(2)*y(19)) - (y(3)*y(19));
  out(21) = (y(3)*y(16)) - (y(2)*y(21)) - (y(3)*y(21))
  out(22) = (y(4)*y(17)) - (y(4)*y(22)) - (y(4)*y(22))
  out(23) = (y(5)*y(17)) - (y(5)*y(23)) + (y(5)*y(23))];
end

MATLAB: Error using trustnleqn (line 28) Objective function is returning undefined values at initial point. FSOLVE cannot continue.

For the original version of the function, there appear to be an infinite number of solutions spaced approximately 3/1509800 /2 apart in the imaginary plane, with real component 57599/850000 . For example one solution is at approximately

57599/850000 -245788448974313916824885/24556871395725172650816064*1i

With the solutions being roughly 1E-6 apart, you would need to use quite fine tolerances on the fsolve to get convergence.

For the revised version, the solutions appear to be closer than 1/100000 apart in the imaginary plane.

Best Answer

Related Solutions

MATLAB: Solvin Differential Algebraic Equations

MATLAB: Error using trustnleqn (line 28) Objective function is returning undefined values at initial point. FSOLVE cannot continue.

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