# To know the units of t span used in ode45 command

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Saraswathi S le 22 Juil 2021
Commenté : Saraswathi S le 22 Juil 2021
I am using ODE45 command to solve 8 ordinary differential equations. My doubt is if im specifying tspan=[0 1000] , what will be the units of time like is it in seconds, minutes, hours?
code:
tspan=[0 1000];
yo=[1;2;3;4;5;6;7;8;9];
[tsol,ysol]=ode45(@filename,tspan,yo];
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James Tursa le 22 Juil 2021
The units of tspan is dictated by how you formulate your differential equation in the function handle. ode45( ) doesn't assume or know anything about units.
Saraswathi S le 22 Juil 2021
Thank you so much Sir

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### Réponse acceptée

Yongjian Feng le 22 Juil 2021
You can type this in the matlab command line window:
help ode45
to get help for ode45 function.
The first input argument is a function handler. This is the function that tells you what t means. In other words, whatever unit of t is used in the function handler, it is also used in the tspan.
Does it make sense?
Thanks,
Yongjian
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Saraswathi S le 22 Juil 2021
Yes, Thank you so much Sir

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### Plus de réponses (1)

Steven Lord le 22 Juil 2021
There is no unit inherent to the t variable used by ode45. Just implement your ODE function correctly for your time units.
If you're solving a physics problem and using standard gravity you should formulate it in seconds.
If you were modeling a predator-prey system using the Lotka-Volterra equations then your time units would probably be years.
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Saraswathi S le 22 Juil 2021
Okay Sir. Thank you so much.

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