if, elseif, else question

Hi everyone,

I have a question regarding "if, elseif, else".

The condition I have is in the following:

When t<65.4, T=473+5*t

t>65.4, T=800

and t<61.4, Coe=0.05+(2*10^(-5))*T

t>61.4, Coe=-10.4+0.024*T-(10^(-5))*T^2

Something is wrong with my code. It did not give the correct answer I've expected. The code I've written is in the following:

function dydt=Hi(t,y)
format long
 
  if t>0 & t< 61.4
     T=473+5*t; 
     Coe=0.05+(2*10^(-5))*T;
  elseif 61.4<t & t<65.4
     T=473+5*t;
     Coe=-10.4+0.024*T-(10^(-5))*T^2;
  else
     T=800; 
     Coe=-10.4+0.024*T-(10^(-5))*T^2;
  end
 
E1=90000;
k10=15000;
k1=k10*exp(-E1/(8.314*T));
n1=1;
 
 
 
A=y(1);
B=y(2);
 
 
dAdt=-k1*(A^(n1)-Coe);
dBdt=k1*(A^(n1)-Coe);
 
dydt=[dAdt; dBdt];


[t,y]=ode45('Hi',[0 250],[14.25 0.75]);
A=y(:,1);
B=y(:,2);

Does anyone know what mistake I've made and how can I revise it? Thank you!

[James Tursa]

Please post the ode equation you are trying to solve.

[Peter O]

I agree with James here. Structurally, your code is fine, and the outputs for A and B appear smooth.

[Robert U]

According to given inequalities values for T are undefined for t = 65.4 whereas values for Coe are undefined for t = 61.4. Your code is assigning the "else"-case for these undefined values. Furthermore it is not defined that first interval is valid only for t > 0 (Even though, t seems to be time. But you did not define that.)

I assume, the inequalities given are not entirely correct since you want to have a functional description that is steadily defined.

Your code jumps into "else" statement for t = 0 which leads to an unsteady output for T and Coe.

Please, elaborate on "It did not give the correct answer I've expected." What have you expected, and what have you got.

Kind regards,

Robert

[Rik]

Is t a vector or a scalar? A conditional should be a scalar, otherwise the result is probably not what you think it would be.