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From: "Dinesh " <revooridinesh@gmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: HOw to solve these type of equations
Date: Sun, 5 Aug 2012 01:38:17 +0000 (UTC)
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> if no y3' then it not differential equation but algebra like in
> school. just move the known to the left and unknown to the right to
> solve and for the first 2 differentials use the matlab od54 functions
> but need initial conditions

Thank you for the reply 
the three equations are functions of y1,y2,y3 and i know the values before time 0-

my original equations are C1*y1' = F*C2*y2 - C3*y1
y2' = C4 -B* C5*y3 - C6*y1
y2-C7=x(t)*y3

X(t) is a known function
where F = 0 when y3<y1
                1 when y3>y1
B=0 when C7<y3
     1 when C7>y3

so what I am thinking is at time t1 i will get the values for F and B depending on previous values and X value will be known and I need the solution for the unknowns at time t1. I tried solving this by newton raphshon method but the solution is not converging.

Thanks a lot