Robert Dodier wrote:
> Mani chandra wrote:
>
>
>> I've attached the value of a particular func where it fails. But
>> this varies though. Also I restarted the code, making sure I evaluate
>> only the problematic part and it works. So, it must be an internal
>> memory limit for Maxima. Is there any way of increasing this?
>>
>
> Memory limits are set by the underlying Lisp implementation.
> I assume you have Maxima + ECL >= 9.2.1.
> If so you can adjust the heap size (in bytes) by executing in Maxima:
>
> :lisp (ext:set-limit 'ext:heap-size nnnnnnnnn)
>
> You can get the default limit by :lisp (ext:get-limit 'ext:heap-size)
> It's probably something relatively small like 256 M.
>
>
>> sin(2*x)*cos(2*y)*cos(2*z) - (-I*u_x0*e^(-I*x - I*y - I*z) - I*u_x1*e^(-I*x
>> - I*y) +
>>
>
> I guess I is the imaginary unit, right? Are u_x0, u_x1, and other u_x
> terms
> constants, or expressions containing x?
>
> There are a couple of things you can try to make this more digestible.
> (1) expand(foo) (where foo = expression you gave) to get a sum of
> simpler terms
> (2) map(integrate, bar) (where bar = expand(foo)) to integrate term by
> term. Not sure if that's really necessary.
>
> My advice is to try these heuristics in addition to increasing the
> heap size.
>
> Can I ask what is the purpose of solving this problem?
> I am always interested to hear what people are working on.
>
> HTH
>
> Robert Dodier
>
>
> >
>
>
Hi,
I'm glad you asked. There a set of equations known as the
Magnetohydrodynamic (MHD) equations which govern the behaviour of
electrically conducting fluids. One obtains these equations from the
Navier-Stokes equations and the Maxwell's equations. Now, the phenomenon
we're interested in is "Dynamos". Dynamos are magnetohydrodynamic
systems with a self-sustaining magnetic field. For example, the Earth is
a dynamo. (More specifically a geo-dynamo). This magnetic field
generation and reversals are a topic of current research and is what
we're working on. We numerically simulate MHD systems with a certain
fixed degrees of freedom (~ millions) and then try to reproduce and
analyse this behaviour using a low dimensional model, which is what the
code I've attached in my first mail, generates. You can find more work
being done by our group at the following website
http://home.iitk.ac.in/~mkv <http://home.iitk.ac.in/%7Emkv>
Regarding, setting the limit on the heap size, the commands which
you gave me don't seem to work. I've tried them in a standalone
installation of Maxima in my system.
Maxima encountered a Lisp error:
SB-INT:SIMPLE-READER-PACKAGE-ERROR at 21 (line 1, column 21) on
#<SB-IMPL::STRING-INPUT-STREAM {100575D161}>:
package "EXT" not found
Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
I'm not sure what implementation of lisp is being used in my Maxima
build and in the one included in SAGE. I couldn't get SAGE to pass those
commands in Maxima. I tried maxima.eval_string(":lisp (ext:get-limit
'ext:heap-size)"). Any suggestions on how to increase the heap size in
the Maxima included in SAGE would be nice.
Thanking you,
Mani chandra
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