[aspect-devel] building a temperature initial condition

Rene Gassmoeller rene.gassmoeller at mailbox.org
Fri Feb 24 16:05:01 PST 2017

Hi Felipe,

While John is right that you can declare several components for a 
function, I am not sure this will help in your specific case, because it 
is impossible (as far as I know) to access one component from another 
component (and the temperature plugin expects only a single component in 
the function anyway). If your 'u' would be a complicated constant, you 
could declare it as 'set Function constants = ...' and access it in your 
function expression. Unfortunately it depends on x,y,z.

So you will probably need to duplicate it in every place of your 
function (you can break lines, I think with '\'?). If you feel the 
function is still to unreadable, you have likely crossed the line, where 
a plugin is more appropriate then a complicated function expression. 
Though from experience where this line is is different for every user (I 
have seen seven line function expressions with multiple if-else 
statements and trigonometric functions, while I switch to writing a new 
plugin as soon as I need more than two lines).



On 02/24/2017 02:31 PM, John Naliboff wrote:
> Hi Felipe,
> deal.II can certainly handle multiple expressions for a given function 
> (https://www.dealii.org/8.4.0/doxygen/deal.II/classFunctionParser.html). 
> I think some of the particle routines in ASPECT also allow for 
> multiple expressions?
> However, if you plan on writing a moderately complicated expression(s) 
> perhaps a plugin is more suitable?
> Cheers,
> John
> *************************************************
> John Naliboff
> Assistant Project Scientist, CIG
> Earth & Planetary Sciences Dept., UC Davis
> On 02/24/2017 10:56 AM, FELIPE ORELLANA ROVIROSA wrote:
>>  Hi all,
>>      I wonder whether it is possible to build up a Temperature 
>> function using several variables. I am working on an initial 
>> condition for Temperature (Function expression)
>>      I am trying to implement something like this
>>      u = u(x,y,z...)
>>      T = f1(u) + f2(u) + f3(u) + ...
>>      In this case, the predefinition of u allows me to save writing. 
>> Otherwise I would need to write the 'long' expression of u on the 
>> Function expression for T several times..
>>     somehow, can the Function expression, or that part of the code, 
>> have more than one function, and do composition of functions ?
>> Is this possible?
>> Felipe
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