[time-nuts] matlab, python, etc.

Bob Camp lists at rtty.us
Mon Jan 7 18:20:50 UTC 2013


Hi

The original spec called out "needs to run Matlab". If that's already a
given, then CPU horsepower is the variable to optimize vs payroll hours.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: Monday, January 07, 2013 12:44 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] matlab, python, etc.

I think you have it backwards.   The purpose of Matlab and things like it
is NOT to save computer time.  It is to have enginerring man hours.   For
example a problem can be coded in two hours in Matlib that would take me a
week to code in C.   But then when you run the software the C coded
solution might run 10X faster and be done in minutes rather than hours.
 But look at the TOTAL time, a day for Matlab a Week for C.  We save much
time and money but we used the computer harder.    Of course those numbers
are just round examples.

If you are building a production system and intend to distribute many
thousands of units then saving cost of the parts matters but if you are
building just 5 or 10 units then the cost of the engineering dominates and
you almost don't care the cost of the parts.    This is the Matlab/C
des=cision too, using something like LabView or Matlab reduces engineering
costs but pushes it out to execution costs.   It depends how many times the
code will be run.  If you will be running it thousands of times per week,
code it in C


On Mon, Jan 7, 2013 at 6:40 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 1/7/13 4:30 AM, Bob Camp wrote:> HI
> >
> > Well if you are getting it done in seconds on Matlab, then you likely
> don't need Matlab very badly. Around here a typical Matlab setup is indeed
> CPU bound for a *lot* longer than that during a normal work day. Two or
> three hours a day is not at all unusual.
>
> I do tons of stuff on Matlab that runs in seconds, because it's a easy and
> facile development environment. Here's a time-nutsy sort of example..
>
> I've been working on systems for time and frequency distribution among
> orbiters and landers at a planet.  Say you're flying one of those
> newfangled Deep Space Atomic Clocks on an orbiter, and you want to
> propagate that to other orbiters or landers.  The questions that come up
> are things like "how much RF power do we need to radiate", "what
> performance is achievable at the lander, for an orbiter with orbit
> parameters X and Y"..
>
> So you've got to run an orbit propagator, then take that data and run it
> through some sort of ad-hoc models for the time/frequency transfer
> performance, and then take that and come up with some meaningful plots to
> put on a slide or in a report.  And then, someone asks, ok, that was for a
> 400km circular orbit around Titan, but what if we make it elliptical with
a
> 2000km apoapsis, oh, and by the way, what's the maximum time we can NOT
run
> the transmitter during periapsis, and still get decent nav performance.
>
>
> sure, I could load up the orbits in something like STK or SOAP, generate a
> file of positions or link analysis, then ingest that into something that
> does the time analysis, etc.
>
> Or, I can just use an existing Matlab toolbox that does the orbit
> propagator, run it through the existing Matlab code that does the link and
> time modeling, and use Matlab to generate the pretty plots.  And when the
> weird question comes up, I can just change a few numbers, re-run it, see
> that it's going to be a disaster, performance wise, go back to them and
> say, "are you sure you want to do that, why not a 1200m apoapsis?" or
> something like that.
>
>
>
> There's a whole lot of stuff that time-nuts do in terms of data analysis
> that is pretty quick and easy in Matlab (or Octave), especially for
> "fooling around".  I'm not wild about Matlab's data acquisition
> capabilities, but then, I'm less wild about LabView (because under it all,
> I'm a "edit the text file, compile and run" kind of guy).
>
> And if you're doing something like filters and control loops, Matlab makes
> it pretty easy, and has a lot of library stuff.  Granted, all this also
> exists for most other languages, e.g. Python.
>
> A couple years ago, I was trying to figure out a way to measure the gain
> and noise behavior of a GPS receiver with just the raw bits from the
> sampler.  Matlab makes it easy to generate data and do the analysis.
>
>
> Ultimately, Matlab (and related products) saves developer time which is
> expensive.  It's faster (wall clock wise) to just call a toolbox routine
> to, say, do some curve fit or digital filter than it is to code it up in
> something else.  This is especially true when the developers are more
> domain knowledge specialists rather than software engineers: they like
> using Matlab, they're familiar with it.
>
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-- 

Chris Albertson
Redondo Beach, California
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