Error in function ?

when I run it I got the following error

Undefined function or variable 'TBack'.

Error in interp (line 18)
TBack;

Error in physio (line 10)
        v=interp(t);

Error in testingfile (line 47)
    p1=physio(t(i)+alfa);

Answer 1

[Jim Riggs]

I think that the statement

TBack;

at the end of the interp function does not belong. Just delete it.

Here is another issue:

In your interp function, you cannot execute the loop for k=1 to length (t_test) because you are referencing element (k+1) this will cause you to have an "out of bounds" subscript error when k=length(t_test).

The loop should run for k=1 to length(t_test)-1

[Willim]

Output argument "TBack" (and maybe others) not assigned
during call to "interp".

Error in physio (line 10)
        v=interp(t);

Error in testingfile (line 47)
    p1=physio(t(i)+alfa);

After changing them I still have the error

[Jim Riggs]

I think that the error with "TBack" is that the function output needs to be defined for all logic paths in the code.

You have one logic path (the first "if" condition) where this variable will not be assigned. You have two choices to fix this:

1) Add a definition for TBack in your first "if" statement, e.g.

if t1 <=0 || t1 >9
    TBack = -99;  
    ...
end
elsif
...   

This represents a "nonsense" condition where the function is undefined.

2) Or you can assign a default value for TBack before the if statement.

This way, TBack will always have a value assigned.

[Willim]

 function [TBack]=interp(t1);
t_test=[0 1 2 4 5 7 8 9];
T = [0 5 8 -6 -6 6 3 -4];

% find the t loction 
for k=1:length(t_test)-1
    if t1 <= 0 || t1 > 9
        fprintf('Undefined \n')
        TBack=-1;
%     elseif t1 == 9
%         TBack= -4;
        break
    elseif t_test(k) <= t1 && t_test(k+1)> t1
        TBack=(((T(k+1)-T(k))/(t_test(k+1)-t_test(k)))*(t1-t_test(k)))+T(k);
    end
end
%TBack;
end

it still has the error

[Willim]

I think it's going well when I change the for loop to 7 , but the result is completely wrong

%% The main 
t=[1e-23 1 2 4 5 7 8 9];
x=1;
alfa=0.1;
h=0;
for i=1:1:7
    p1=physio(t(i)+alfa);
    p2 = physio(t(i));
    h(i)=alfa*(p1- p2)
    x(i+1)=x(i)*(1+0.8*h(i)*(1-(x(i)/25)))
end
plot(t,x)
hold on
title('The Locistic Model of a Population System Driven by physiological time')
xlabel('Time ,t')
ylabel('Population Size')
%% ode 45
tspan = [0 9];
x0 = 1;
[t,y] = ode45(@(t,x) 0.8*x*(1-(1/25)*x), tspan, x0);
plot(t,y)
grid on 
title('The Locistic Model of a Population System Driven by Chronological time')
xlabel('Time ,t')
ylabel('Population Size')

[Jim Riggs]

If you are intending to interpolate T using t_test , then the correct formula is:

TBack = (t1-t_test(k))/(t_test(k+1)-t_test(k)) * (T(k+1)-T(k)) + T(k);

[Jim Riggs]

I just noticed that you commented out the condition

elseif t1 == 9    

If you do this, then you should change the conditional on the next statement from

elseif t_test(k) <= t1 && t_test(k+1) > t1

to

elseif t_test(k) <= t1 && t_test(k+1) >= t1

otherwise, there is no defined action for t1 = 9.

[Jim Riggs]

I'm afraid that I cannot help you if you do not like the results, since I do not understand the problem you are working.

But if I have been helpful, please accept my answer.

Perhaps you should clean up your code, and then post a new question showing the code and the results you are getting, and why you think it is not right (i.e. what is the expected result?). Maybe someone else knows about this particular type of problem.