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Re: How to solve or approximate a first order differential equation ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg123245] Re: How to solve or approximate a first order differential equation ?
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Tue, 29 Nov 2011 07:03:25 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jasv6s$762$1@smc.vnet.net> <javp9t$jap$1@smc.vnet.net>

On Nov 28, 2:54 am, Dino <dinodebla... at gmail.com> wrote:
> Hello and thanks for your reply,
>
> I have a list like this(these are the first terms:
> data = {{1.1795*10^-12, 0.}, {1.1795*10^-12, 0.000011918},
> {1., 0.0000276853}, {1., 0.000027194}, {1., 0.0000242474},
> {1., 0.0000267025}, {1., 0.0000281765}, {1., 0.0000276853},
> {1., 0.000031607}, {1., 0.0000276853}, {1., 0.000027194},
> {2., 0.0000262109}, {2., 0.0000232628}, {2., 0.0000379602},
> {2., 0.0000355202}, {2., 0.0000311167}, {2., 0.000035031},
> {2., 0.0000306263}, {2., 0.0000374716}, {2., 0.0000360052},
> {3., 0.0000306263}, {3., 0.0000203098}, {3., 0.0000355202},
> {3., 0.0000384486}, {3., 0.0000345417}, {3., 0.0000345417},
> {3., 0.0000237551}, {3., 0.0000252315}, {3., 0.0000257192},
> {4., 0.0000237551}, {4., 0.0000267025}}
>
> and it gives me some errors. Is that possible to keep only a selected
> amount of data, because it would be easier to work with a less amount
> of data.
> Furthermore the first terms {xi, ...} are repeated because there are
> more measures for each second. How to keep only one value for each
> {xi, ...} ?

Use the means:

{#, Mean@Cases[data,{#,_}][[All,2]]}& /@ Union@data[[All,1]]

{{1.1795*^-12, 5.959*^-6},
 {1., 0.0000275753},
 {2., 0.0000325783},
 {3., 0.0000298549},
 {4., 0.0000252288}}

> In conclusion I would like to keep only for example 50 terms from the
> list of data and make the model work as you showed.
>
> Thanks,



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