jiju | 23 Apr 21:30 2014
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Steps invoived in the calculation

Hi,

Is there any way to obtain all the steps involved in the mathematical calculations from sympy?

Thanks,
Jiju

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Alangi Derick | 23 Apr 13:00 2014
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Introduction

Good day to all the SymPy developer,
                   I am Alangi Derick and i am a sophomore in the University of Buea, Cameroon. I was looking at the organisations that was accepted by Google to participate in this years GSoC program(2014), i saw this great organisation called(SymPy) which interest me the most because i am a python programmer an i really want python to be my mother language. So i have decided that i am going to start working from now so that i get to understand the codebase of SymPy and participate in this organisation for the next years GSoC program(2015). I belong to the faculty of Engineering and specifically, the department of Computer Engineering. Like i said earlier, my intension is to make this software(Library) a successful on after i contribute to it and see it go a long way to the end users of it.
                    Thanks for your understanding.

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Ivica Nakić | 23 Apr 01:30 2014
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converting expression into function

Hi,

is there a simple way to convert an expression into a function?

For example, the solution of ODE by the function dsolve returns an expression, and I would like to define the corresponding function so I can write something like f(1) instead of f.subs(x,1).

Thanks,
Ivica

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Amit Saha | 22 Apr 22:28 2014
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Advise regarding using strings in SymPy

Hello all,

In my early days of exploring SymPy, I found often  that one *could*
use strings as arguments to various SymPy's functions, instead of
passing Symbol objects. A case in point is the solve() function. For
example:

>>> expr = input('Enter an expression: ')

Enter an expression: x + 3*y - 6
>>> expr = sympify(expr)
>>> solve(expr, 'y')
# get the solution back.

However, I have also learned along the way (from you all) that this is
not be relied upon. I shouldn't really use strings here.  So, I
thought that (something along these lines) is the more correct
approach:

# For example:
for s in expr.atoms(Symbol):
if s.name == 'y':
     solutions = solve(expr, s)

So, I think the latter is the approach I should really follow myself
and also tell others since that is the right thing to do?
Suggestions/comments are very welcome.

Thanks,
Amit.
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Amit Saha | 22 Apr 22:04 2014
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More specific parsing error?

Hello,

Consider the following:

>>> expr=input('Enter a mathematical expression: ')

Enter a mathematical expression: x**2 + 3x + x**3 + 2x

>>> expr = sympify(expr)

Traceback (most recent call last):

File "<pyshell#146>", line 1, in <module>

expr = sympify(expr)

File "/usr/lib/python3.3/site-packages/sympy/core/sympify.py", line
180, in sympify

raise SympifyError('could not parse %r' % a)

sympy.core.sympify.SympifyError: SympifyError: "could not parse 'x**2
+ 3x + x**3 + 2x'"

Is it possible to get a more specific error message here? Like which
of the terms are invalid, for example?

Thanks,
Amit.

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jiju | 22 Apr 22:01 2014
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Using sympy for a web application

Hi,

I have successfully installed sympy in server and has gone through various mathematical operations and plots it is able to perform.

My goal is to have a web application (php) which will communicate with sympy to get the answers and graphs for various algebraic expressions.

What I plan to do is
1. create a python script which will take the expression as a command line argument, execute it using sympy  and return the result.
2. From php, call this python script and retrieve the result.

I have succeeded in getting it worked except for graphs. But certainly, this are better ways of doing it .

Could you please guide me on the approach I need to follow to get graphs and results in html format from sympy ?


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Aaron Meurer | 22 Apr 18:13 2014
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Questions about the goals of CSymPy

I have some high level questions about CSymPy.

- What are the goals of the project?

- What are the things that should definitely go in CSymPy?

- What are the things that should definitely not go in CSymPy?

- How will CSymPy be architectured to allow things to happen in CSymPy
when they can but fallback to SymPy when they cannot.

My main concern here is that CSymPy has not clear separation from
SymPy, and as a result it will end up growing larger and larger, until
it becomes an independent CAS (which is fine if that's the goal, but
my understanding was that it was supposed to be just a small fast
core).

In particular, if there is some feature of SymPy functions, how will
CSymPy be architectured so that it can take advantage of it without
having to completely reimplement that function in C++?

For instance, a current goal of CSymPy is to implement trig functions.
But this can be quite complicated if you consider all the different
things you can do with trig functions. Without even thinking about
trig simplification, there are complicated evaluation issues (e.g.,
consider sin(pi/7).rewrite(sqrt) in SymPy). It would be a shame to
reimplement all this logic twice, especially it is not needed for
performance.

Finally, I noticed that the CSymPy Python API doesn't adhere to SymPy
standards, e.g., it doesn't use .args. I think a first step in this
direction would be to make all CSymPy objects completely compatible
with SymPy. Probably a good idea would be to mixin Basic to all CSymPy
classes (is this possible?).

Aaron Meurer

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Kevin Bockstael | 22 Apr 10:11 2014
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including external forces with KanesMethod of LagrangesMethod


Hi

I would like to include a periodic external force into a multiple mass damper-system. My first thought was to include it in the forcelist (using KanesMethod)
which would then become something like in the code below. (where b is the frequency of the periodic force)
This however, returns an error whenever i want to integrate the dynamical equations.
Does anyone know how to include the external force f(t) = sin(b*t), so i can integrate the dynamical equations? 

Thanks

q1,u1,q2,u2 = dynamicsymbols('q1 u1 q2 u2')
q1d, q2d = dynamicsymbols('q1 q2',1)
m1,c1,k1, m2,c2,k2, g,t,b = symbols('m1 c1 k1 m2 c2 k2 g t b')
N = ReferenceFrame('N')
O=Point('O')
O.set_vel(N,0)
P = Point('P')
P.set_vel(N,-u1*N.y)
Q=Point('Q')
Q.set_vel(N,-(u2+u1)*N.y)
kd=[q1d-u1,q2d-u2]
FL = [(P,(2*k1*q1-k1*q2+c1*u1)*N.y),(Q,((k1+k2)*q2-k1*q1+c2*u2+sin(b*t))*N.y)]

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SAHIL SHEKHAWAT | 22 Apr 06:26 2014
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Web Backend for SymPy

I personally feel that like other CAS ( mathematica for example )  in order to increase our user-base we need to extend to the web and add parsing functionality (was also a GSOC proposed project) so that anyone without much know-how can use it. I am not sure how strongly other experienced developers feel about it but i want to do this. We already have SymPyGamma but not much it being done to improve it which is a bit upsetting.

To do that i seek everyone's suggestions about the project which i proposed as my GSOC proposal:
https://github.com/sympy/sympy/wiki/GSoC-2014-Application-Sahil-Shekhawat%3A-Web-based-backend-for-SymPy%27s-plotting-module-and-3D-plotting
Is there something which i must not do or something which i missed ?

I can not commit full time so it might be slow but i will try my best. Please help me to make SymPy even better
Thanks

Sahil Shekhawat

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Aaron Meurer | 21 Apr 21:52 2014
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GSoC projects announced

Hi everyone.  As many of you may have noticed, Google has announced the
results for Google Summer of Code.  I am proud to announce that we got ten
slots from Google.  The following projects have been accepted:

Student (Project): Mentor

- Akshay Narasimha (Improvements to the Geometry Module): Stefan Krastanov

- Avichal Dayal (Series Expansion): Sergey Kirpichev, Stefan Krastanov

- Harsh Gupta (Improving Equation Solvers): Matthew Rocklin, Sergey Kirpichev

- Jim Crist (Linearization Routines for Equations of Motion): Oliver
Lee, Luke Peterson

- Kundan Kumar (Implementation of system of ODEs and Improvement of ODEs
  solving Engine): Sean Vig, Tim Lahey

- Sachin Joglekar (sympy.vector module): Jason Moore

- Soumya Dipta Biswas (Implementation of Propositional and First Order Logic
  in SymPy): Aaron Meurer

- Sudanshu Mishra (Introducing Optics module): Sean Vig, Ondřej Čertík

- Sushant Hiray (Extending Elementary Functions in CSymPy): Ondřej Čertík

- Thilina Rathnayake (Linear Algebra Module for CSymPy): Ondřej Čertík

Additionally, the following proposal will be accepted through the PSF with PyDy.

- Tarun Gaba (PyDy Viz Improvements and Enhancements): Chris Dembia, Jason
  Moore

Join me in congratulating these students on their acceptance.

In case you don't know, Google Summer of Code is a program where Google pays
students to write code for open source projects.  SymPy was accepted as a
mentoring organization this year.  The goal of the program is to help the
students learn new skills, in particular in our case:

* contributing to opensource
* working with the community
* learn git, pull requests, reviews
* teach them how to review other's people patches
* do useful work for SymPy
* have fun, and encourage the students to stay around

To all the students who are accepted, you should be receiving an email from
your mentor soon to discuss how you will be communicating over the summer
about your project.  You should meet with your mentor about once a week during
the summer to go over your progress.  You should either meet on a public
channel (like Gitter), or else post minutes of your meeting in some public
channel, so that the whole community can see your progress too.

As I suggested on the mailing list earlier this year, we may also want to try
doing Google+ hangouts this year.  Face to face chats can be very effective.
And you can make the hangout public, so that people can watch it in real time,
and the video will be uploaded to YouTube so that people can watch it later as
well if they want.

Another idea is to use Gitter custom channels.  Be sure to make them public
and share the link if you do.

Some of you have been assigned two mentors.  They will both work to keep you
on track for different aspects of your proposal.  If you have two mentors and
one is not available for something, or does not know the answer, you can ask
the other.

I would like all of us to strongly encourage students this summer to submit
pull requests early and often.  This will go a long ways towards making sure
that you don't end the summer with a ton of code written that never gets
merged.  Students should help review pull requests by other students, so that
we don't get bogged down reviewing so much code.

We also require that all students keep a weekly blog of their work over the
summer.  If you don't already have a blog, you should start one.  I recommend
using either Wordpress, Blogger, or creating your own blog on GitHub pages.
If you are savvy enough to set it up, I recommend GitHub pages, but if you
aren't, both Wordpress and Blogger are good enough.  The only requirement is
that it has an RSS feed, so we can put it on planet.sympy.org.  I also
recommend that it have some kind of comments box, so that people can comment
on your work.  Once you have set up your blog, send a pull request adding it
to https://github.com/sympy/planet.sympy.org/blob/master/planet.ini.

Starting on the week of May 19 (when the GSoC period officially begins), we
will expect you to have at least one blog post a week, describing your
progress for that week, or something interesting about your project.  If you
don't have a post by the beginning of the day on Saturday, your mentor or I
will email you to remind you about it.

I will also blog throughout the summer on own blog at
http://asmeurersympy.wordpress.com/. I invite other mentors who have blogs to
do the same.  And I encourage all community members to follow and comment on
the student blogs, so you can see their progress.

I would like to thank all the students who applied this year and everyone who
submitted a patch.  I would also like to thank all the mentors for helping
review patches and proposals.

This summer is looking to be another very productive one for SymPy, and I look
forward to it!

Aaron Meurer

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jiju | 21 Apr 20:19 2014
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Basic execution - SymPy

Hi,

I have successfully installed SymPiy. Consider the following python  script test.py with output -sin(x) as expected

from sympy import *
var('x')
print diff(cos(x), x)

I would like to pass diff(cos(x), x) as a command line argument to python  script as python test.py  diff(cos(x), x). Could you help me in how to execute this then?

I tried to use print os.system(sys.argv[1]) which is not working! Thanks in advance



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