Array indices must be positive integers or logical values.

Error in TASKA (line 22)

A(t)=(A0-B0/YB)./(1-(B0/(YB*A0))*exp(-((YB*A0/B0)-1)*K*B0.*t));

[David Hill]

What is the value of t? The only thing you are indexing into is A. The error appears to tell you that t is not a positive integer or logical value.

[Navaneetha Krishnan Murugadoss]

ti=0;

tf=12;

[David Hill]

You cannot index with 0 (indexing for matlab starts at 1)

[Navaneetha Krishnan Murugadoss]

my initial value is 0 and final value is 12 hours i need to find the value inbetwwen this time

[David Hill]

Cannot help further unless you provide more information (all variables with values and context)

Answer 1

[Image Analyst]

A thorough discussion is in the FAQ:

https://matlab.fandom.com/wiki/FAQ#.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22

In the meantime, try getting rid of (t) on the left hand side.

A = (A0-B0/YB) ./ (1-(B0/(YB*A0)) .* exp(-((YB*A0/B0)-1)*K*B0 .* t));

Answer 2

[Navaneetha Krishnan Murugadoss]

clc
clear all
YB=1;
YP=0.15;
A0=1;
B0=3;
P0=0;
K= 5E-5;
ti=0;
tf=12;

F=@(t,y)[-K*y(1)*y(2);-YB*K*y(1)*y(2);YP*K*y(1)*y(2)];

% create function of ODE

% f = [da/dt;db/dt,dp/dt]

[t,y]= ode89(F,[ti tf],[A0;B0;P0]);

%ODE89

A(t)=(A0-B0/YB)/(1-(B0/(YB*A0))*exp(-((YB*A0/B0)-1)*K*B0*tf));

% Analytical solution

plot(tf,y(:,1),'-0',tf,A_t','-*')
title('Solution of ODE with ODE89 and comparison with Analytical value');
xlabel('Time t');
ylabel('solution A(ODE89)& A(t) Analytical Value');
xlabel('Time t');
ylabel('solution A (ODE89) & A(t) Analytical value');
xlabel('Time t');
ylabel('Solution A(ODE89) & A(t) Analytical ');

legend('A(ODE89)','A(t) Analytical')

disp('time A(ODE89) A(t) Analytical ')

disp([tf y(:,1) A_t])

[Image Analyst]

You posted this as the "Answer".

So, did this "Answer" of your fix it? Otherwise take another look at my answer.

[Navaneetha Krishnan Murugadoss]

I tried using removing t in A but it shows

Error using plot

Invalid color or line style.

Error in TASKA (line 26)

plot(tf,y(:,1),'-0',tf,A,'-*')

[Walter Roberson]

plot(rand(1,5), '-o')

plot(rand(1,5), '-O')

plot(rand(1,5), '-0')

Error using plot
Invalid color or line style.

which is to say that your '-0' is dash-zero and that is not a recognized line style or color. Using dash-oh or dash-capital-oh is fine.