Input undefined in a function describing differential equations

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I am new at learning how to use the differential equation solvers in MATLAB. I am trying to work out epidemic model differential equations. I got this tutorial online regarding my subject and I tried to use it. The function is given below:

function ypsir =ypsir(t,y)
a = .01;
b = .1;
ypsir(1) =-a*y(1)*y(2);
ypsir(2) = a*y(1)*y(2)-b*y(2);
ypsir(3) = b*y(2);
ypsir = [ypsir(1) ypsir(2) ypsir(3)]';

but when I run it, it keeps on saying input y is undefined. Can someone pls help! Thanks in advance

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Azzi Abdelmalek 2013-5-3

编辑：Azzi Abdelmalek 2013-5-3

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You can not run a function, you should call it.

Look at ode45

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Ojaswita 2013-5-4

编辑：Azzi Abdelmalek 2013-5-4

在 MATLAB Online 中打开

Thanks... i am creating another m file that calls this function, and its giving me an error... in the line that i am using to call the function. Again, this is from the same tutorial that i was using...

to = 0;
tf =50;
yo = [99 1 0];
[t y] = ode45('ypsir',[to tf],yo);
plot(t,y(:,1),t,y(:,2),t,y(:,3))

Zhang lu 2013-5-4

编辑：Zhang lu 2013-5-4

do ypsir.m file you called at your matlab current folder, if not ,do it.

Input undefined in a function describing differential equations

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