Math Forum Discussions

shatrah

Posts: 11
Registered: 1/26/14

Re: Differential equation and ode45 or ode15i
Posted: Jan 27, 2014 10:25 PM

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"Steven Lord" <Steven_Lord@mathworks.com> wrote in message <lc6dl9$mlf$1@newscl01ah.mathworks.com>...
>
> "shatrah " <shatrah1978@gmail.com> wrote in message
> news:lc63k7$dh3$1@newscl01ah.mathworks.com...
> > "Torsten" wrote in message <lc5tqg$495$1@newscl01ah.mathworks.com>...
> >> "shatrah " <shatrah1978@gmail.com> wrote in message
> >> <lc5sso$kdh$1@newscl01ah.mathworks.com>...
> >> > "Torsten" wrote in message <lc5r64$o8h$1@newscl01ah.mathworks.com>...
> >> > > "shatrah " <shatrah1978@gmail.com> wrote in message
> >> > > <lc5q4c$4a9$1@newscl01ah.mathworks.com>...
> >> > > > "Torsten" wrote in message
> >> > > > <lc5mi0$n5t$1@newscl01ah.mathworks.com>...
> >> > > > > "shatrah " <shatrah1978@gmail.com> wrote in message
> >> > > > > <lc35in$d3g$1@newscl01ah.mathworks.com>...
> >> > > > > > dq/dz=dy/dz+q dy/dz=z*y
> >> > > > > > ds/dz=dy/dz+dq/dz y=10, dy/dz=0 for z=0
> >> > > > > > z=15, dz/dz=0 for z=0
> >> > > > > > q=11, dq/dz=0 for z=0
>
your answer on ode15i but my question on ode45 ?
> *snip*
>
> > Thanks fo reply ....
> > Please just answe this questin ( my clear one ) Can I use this on matlab
> > ode45 , dy(1)=dy(2)+d(3) ???? Or must left side contain only dy and right
> > side don't contain dy ??? Clear question !!! Thanks
>
> For a system like this, use a mass matrix. See the "Mass Matrix and DAE
> Properties" section on this page:
>
> http://www.mathworks.com/help/matlab/ref/odeset.html
>
> Rewrite your system as:
>
> dq/dz - dy/dz = q
> dy/dz = z*y
> - dy/dz - dq/dz + ds/dz = 0
>
> For this system, your mass matrix would be:
>
> [1 -1 0; 0 1 0; -1 -1 1]
>
> Your f(t, y) would then return [q; z*y; 0], and the solutions would be
> [dqdz; dydz; dsdz].
>
> --
> Steve Lord
> slord@mathworks.com
> To contact Technical Support use the Contact Us link on
> http://www.mathworks.com