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diff eq
Posted:
Apr 7, 2013 9:33 AM


I am trying to use ode45 to to solve a system of first order linear diff eq They are a set of 4 diff eq X'=AX where X' is a 4x1 column matrix of dx_i/dt where i= 1,2,3 or 4 A is 4x4 matrix of time independent values (ie coefficient values) X is a 4x1 column matrix of x_i(t) where i= 1,2,3 or 4
this is what I am typing into MATLAB: function dx = system_ex(t,x) dx = zeros(4,1); dx(1) = 2.4712*x(1) + 0.005*x(2) + 0.56*x(3)+ 0.1*x(4); dx(2) = 0.385*x(1)  0.1002*x(2) dx(3) = 0.002*x(2)  0.6462*x(3) dx(4) = 0.007*a(2)  0.2042*x(4) [T,X] = ode45(@systems_ex,[0 10],[1 0 0 0]) plot(t,x(:,1))
and it is returning 'Input argument "x" is undefined' and dx(1) = 2.4712*x(1) + 0.005*x(2) + 0.56*x(3)+ 0.1*x(4); error in line 3 of my code
I am not understanding the 'input arg x is undefined I am trying to let the x_i's to be activities in compartments of a biological system as a function of time, which I am trying to solve for in the diff eq. How would I let MATLAB know this?
any help will be appreciated



