Why I get error to solve this ODE with euler method?

Question

cindyawati cindyawati 2023-4-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1942389-why-i-get-error-to-solve-this-ode-with-euler-method

编辑： cindyawati cindyawati 2023-4-6

Hello, I need to solve this equation with euler method but I got error in array

This equation is:

dMn(t) dt = Kn-1M1(t)Mn-1(t) - KnM1(t)Mn(t) - μnMn(t)

and my code in MATLAB is

%Metode Euler

%dMn/dt= Kn-1*M1(t)*Mn-1(t)-Kn*M1(t)*Mn(t)-Mun*Mn(t)

clc;clear;

%initial variabel

sigma = 50;

K1 = 10^-4;

K0 = 0.1;

n = 6;

Oa = 10;

Pa = 100;

mui = 10^-3;

muo = 10^-4;

mup = 10^-5;

dt = 0.001;

t = 0:dt:100;

n = zeros(length(t),1);

M(1)= 2;

Mn = 0:6;

Kn = K1*M(t)*M(1)-K1*M(1)*M(t)-mui*M(t);

for i = 1:length(t)-1

K(i+1) = K(i)*M1(i)*Mn(i)-K(i)*M1(i)*Mn(i)-mui(i)*Mn(i) ;

end

and MY ERROR IS

Array indices must be positive integers or logical values.

2 个评论
显示无隐藏无

Dyuman Joshi 2023-4-6

在 MATLAB Online 中打开

You are trying to use non-integral values (variable t) as indices to define Kn, which is not allowed.

As the error states array indices must be positive integers.

Are you trying to solve an ODE?

dt = 0.001;
t = 0:dt:100;
Kn = K1*M(t)*M(1)-K1*M(1)*M(t)-mui*M(t);
Array indices must be positive integers or logical values.

cindyawati cindyawati 2023-4-6

yes, i trying to solve ODE with euler

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Luca Ferro 2023-4-6

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1942389-why-i-get-error-to-solve-this-ode-with-euler-method#answer_1210439

First a suggestion, this line really doesn't make any sense:

M(1)= 2;

just do

M=2;

and you get the same result and you don't have to carry around extra syntax. Still i'm not sure that you wanted M as a double since you use it as an array later.

Then the error is on line:

Kn = K1*M(t)*M(1)-K1*M(1)*M(t)-mui*M(t);

You are trying to access a double (M) as if it was an array with M(t). M has only one element and using an index on it doesn't really work. What's more is that the index that you are using later, dt, is not an integer, meaning that it cannot be resolved anyways. What's the element 0.1 in an array? Positions only go by integers, so 1,2,3,...

Later in the code at line:

K(i+1) = K(i)*M1(i)*Mn(i)-K(i)*M1(i)*Mn(i)-mui(i)*Mn(i) ;

you use a variable that doesn't exist, M1. This will throw an error as well

I would suggest a solution but i'm very confused by what we are trying to achieve.

Also if you could write the equation in LateX it would be better.