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

functionMATLABsyms

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),'-.')

Best Answer

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),'-.')
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