CODEWITHSUNDEEP
matlabode
axel
axel

Reputation: 15

EDIT: how to pass ode parameters in second function-Matlab

I have a dynamical system ode, which I need to solve for various values of one of its parameters, the parameter r. However, the function sigm (sigmoid function), appears many times in the system and it was considered preferable to code it as a separate function outside of the system. 

r = 0:+0.01:1;
time = 0:.01:10;
y0 = [0 0 0 0 0 0 0 0]; 
y = NaN(length(time),length(y0),length(r));

for i=1:length(r)
    [t,y(:,:,i)] = ode45(@(t,y) ode(t,y,r(i)),time, y0);
    ...
end

function dydt = ode(~,y,r)

    dydt = NaN(8,1);

    dydt(1) = y(5);
    dydt(2) = y(6);
    dydt(3) = y(7);
    dydt(4) = y(8);
    dydt(5) = sigm(y(3)-y(4)) - y(5)- y(1);
    dydt(6) = sigm(y(3)-y(4)) - y(6) - y(2);
    dydt(7) = sigm(y(1)) - y(7) - y(3);
    dydt(8) = sigm(y(2)) - y(8) - y(4);
end

function X = sigm(u,r)
    X = 1/(1+exp(r*(6-u)));
end

The point where i am having a difficulty is that, the parameter r, only appears in the sigmoid function and not in the ode. Thus, when I am trying to solve the system for many values of this parameter, i get error not enough input arguments.

How can I pass this parameter into the second function?

A potential way, would be to put the whole sigm function, within the ode function:

function dydt = ode(~,y,r)

    dydt = NaN(8,1);

    dydt(1) = y(5);
    dydt(2) = y(6);
    dydt(3) = y(7);
    dydt(4) = y(8);
    dydt(5) = sigm(y(3)-y(4)) - y(5)- y(1);
    dydt(6) = sigm(y(3)-y(4)) - y(6) - y(2);
    dydt(7) = sigm(y(1)) - y(7) - y(3);
    dydt(8) = sigm(y(2)) - y(8) - y(4);

    function X = sigm(u)
            X = 1/(1+exp(r*(6-u)));
    end
end

, but I am guessing it is not a good coding tacticts

Upvotes: 0

Views: 32

Answers (1)

Lutz Lehmann
Lutz Lehmann

Reputation: 25992

Within the function declaration 

function dydt = ode(~,y,r)

the parameter r is defined as a local variable that can then be used like any other scalar value, such as passing it as the second parameter to sigm, like in

dydt(5) = sigm(y(3)-y(4), r) - y(5)- y(1);

Upvotes: 1

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