How to define variables in the main program instead of in the function file

I want to use a loop in the main program to make

a

the different value, and then get different graphics, but without defining

a

in the function file it can't run, how to solve, thank you!

codes are as this

function file

function f = rigid(t,y)

syms a

f = zeros(2,1);    % a column vector
f(1) = a*y(2) * y(1);
f(2) = -y(1) * y(2);

main program

a=1;

options = odeset('RelTol',1e-4,'AbsTol',[1e-4 1e-4]);
[T,Y] = ode45(@rigid,[0 12],[1 1],options);

plot(T,Y(:,1),'-',T,Y(:,2),'-.')

Answer 1

[madhan ravi]

function f = rigid(t,y,a)
% syms a %% not needed
f = zeros(2,1);    % a column vector
f(1) = a*y(2) * y(1);
f(2) = -y(1) * y(2);

%-------
a=1;
options = odeset('RelTol',1e-4,'AbsTol',[1e-4 1e-4]);
[T,Y] = ode45(@(t,y)rigid(t,y,a),[0 12],[1 1],options);
plot(T,Y(:,1),'-',T,Y(:,2),'-.')

[dcydhb dcydhb]

it there any other methods ,because i have many other parameters to change, and

a

is just a simple example.

[madhan ravi]

That was also an example you can change other parameters too , it's called parameterization see the link below:

https://in.mathworks.com/help/matlab/math/parameterizing-functions.html

for a = 1:10
    options = odeset('RelTol',1e-4,'AbsTol',[1e-4 1e-4]);
    [T,Y] = ode45(@(t,y)rigid(t,y,a),[0 12],[1 1],options);
    plot(T,Y(:,1),'-',T,Y(:,2),'-.')
end

[dcydhb dcydhb]

solve the problem and thanks a lot!!!