Hey there people of the mailing list! Below is a copy of an email I
sent to Ondrej
asking about how I can do something for my project....anyone got any
ideas please help! :)
Hi there Ondrej...
I love your project, I would like to support it once I have gotten my
head round it a bit more...
I have two problems with using sympy with numpy for my 4th year
master's project (which, of course,I will release under GNU when all
is said and done...)
The first is that I want to build up function expressions like:
x=sympy.Symbol('x')
a=[1,2,3]
fn=a[0]sin(a[1]*x)+a[2]
and be able to change the values of the elements of the list/array to
change the values of the function parameters (without having to hand
code it using def function(), my algorithm involves generating
different functions with different parameters by operating on existing
sympy function objects)
so the above would give me fn=1*sin(2*x)+3
and I would like to be able to change, say, a[2]=4 so that a=[1,2,4]
and
fn=1*sin(2*x)+4
The above may be enough to solve my problem, in the course of my
project I have
also found the need to interface with scipy.optimise.leastsq() which
is proving more difficult than I expected. I found a better least
squares Levenberg-Marquardt implementation (based on MINPACK fortran
routines) but would need to 'unsympify' my sympy function in order to
use it. Is there some way I can convert from sympy functions to numpy
functions, as I think the reverse is possible with sympify()?
Thank you very much in advance for any help you can give me (I have
found information to be sparse, I intend also to write an introduction
to scientific programming with scipy/sympy/Scientific/pyMPI based on
my experiences when I have finished).
Tim Varkalis
p.s. just thought i'd add, at the moment I'm going the rather
inefficient route of
building strings containing "def fn(blah, blah):\n\t <generated
function>" and then
evaluating them with exec(string). I have yet to see how well numpy
and/or
Scientific deal with differentiating functions constructed in this
way...
BTW does anyone know why eval(string) doesn't handle escape
characters? they
just passed through giving me syntax error....
Anyways, would love to hear thoughts from anyone/everyone
interested...
Cheers, Tim
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