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• Sympy python circumference

  - by Mattia Villani

  I need to display a circumference. In order to do that I thought I could calculata for a lot of x the two values of y, so I did: import sympy as sy from sympy.abc import x,y f = x**2 + y**2 - 1 a = x - 0.5 sy.solve([f,a],[x,y]) and this is what I get: Traceback (most recent call last): File "<input>", line 1, in <module> File "/usr/lib/python2.7/dist-packages/sympy/solvers/solvers.py", line 484, in solve solution = _solve(f, *symbols, **flags) File "/usr/lib/python2.7/dist-packages/sympy/solvers/solvers.py", line 749, in _solve result = solve_poly_system(polys) File "/usr/lib/python2.7/dist-packages/sympy/solvers/polysys.py", line 40, in solve_poly_system return solve_biquadratic(f, g, opt) File "/usr/lib/python2.7/dist-packages/sympy/solvers/polysys.py", line 48, in solve_biquadratic G = groebner([f, g]) File "/usr/lib/python2.7/dist-packages/sympy/polys/polytools.py", line 5308, i n groebner raise DomainError("can't compute a Groebner basis over %s" % domain) DomainError: can't compute a Groebner basis over RR How can I calculate the y's values ?

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• Is there something like Sympy for Java?

  - by Shane Fulmer

  I'm looking for a symbolic math library for Java along the lines of sympy for Python. Does anyone know of anything? Thanks!

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• Using "from __future__ import division" in my program, but it isn't loaded with my program

  - by Sara Fauzia

  I wrote the following program in Python 2 to do Newton's method computations for my math problem set, and while it works perfectly, for reasons unbeknownst to me, when I initially load it in ipython with %run -i NewtonsMethodMultivariate.py, the Python 3 division is not imported. I know this because after I load my Python program, entering x**(3/4) gives "1". After manually importing the new division, then x**(3/4) remains x**(3/4), as expected. Why is this? # coding: utf-8 from __future__ import division from sympy import symbols, Matrix, zeros x, y = symbols('x y') X = Matrix([[x],[y]]) tol = 1e-3 def roots(h,a): def F(s): return h.subs({x: s[0,0], y: s[1,0]}) def D(s): return h.jacobian(X).subs({x: s[0,0], y: s[1,0]}) if F(a) == zeros(2)[:,0]: return a else: while (F(a)).norm() > tol: a = a - ((D(a))**(-1))*F(a) print a.evalf(10) I would use Python 3 to avoid this issue, but my Linux distribution only ships SymPy for Python 2. Thanks to the help anyone can provide. Also, in case anyone was wondering, I haven't yet generalized this script for nxn Jacobians, and only had to deal with 2x2 in my problem set. Additionally, I'm slicing the 2x2 zero matrix instead of using the command zeros(2,1) because SymPy 0.7.1, installed on my machine, complains that "zeros() takes exactly one argument", though the wiki suggests otherwise. Maybe this command is only for the git version.

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• how to handle an asymptote/discontinuity with Matplotlib

  - by Geddes

  Hello all. Firstly - thanks again for all your help. Sorry not to have accepted the responses to my previous questions as I did not know how the system worked (thanks to Mark for pointing that out!). I have since been back and gratefully acknowledged the kind help I have received. My question: when plotting a graph with a discontinuity/asymptote/singularity/whatever, is there any automatic way to prevent Matplotlib from 'joining the dots' across the 'break'? (please see code/image below). I read that Sage has a [detect_poles] facility that looked good, but I really want it to work with Matplotlib. Thanks and best wishes, Geddes import matplotlib.pyplot as plt import numpy as np from sympy import sympify, lambdify from sympy.abc import x fig = plt.figure(1) ax = fig.add_subplot(111) # set up axis ax.spines['left'].set_position('zero') ax.spines['right'].set_color('none') ax.spines['bottom'].set_position('zero') ax.spines['top'].set_color('none') ax.xaxis.set_ticks_position('bottom') ax.yaxis.set_ticks_position('left') # setup x and y ranges and precision xx = np.arange(-0.5,5.5,0.01) # draw my curve myfunction=sympify(1/(x-2)) mylambdifiedfunction=lambdify(x,myfunction,'numpy') ax.plot(xx, mylambdifiedfunction(xx),zorder=100,linewidth=3,color='red') #set bounds ax.set_xbound(-1,6) ax.set_ybound(-4,4) plt.show()

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• Is it possible to plot implicit equations using Matplotlib?

  - by Geddes

  Hello all - many thanks again to people who have kindly offered help (especially to Mark for his outstanding response to my previous question). I would like to plot implicit equations (of the form f(x,y)=g(x,y) eg. x^y=y^x) in Matplotlib. Is this possible? All the best, Geddes

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• Developing a Configurable Pricing Program

  - by Ben DeMott

  The organization I work at has some interesting requirements when it comes to pricing for online commerce. Currently the developers write different 'pricing rules' and those rules can be applied to our items based on attributes of the items. For Example: INPUTS: [cost, sug_retail, discontinued, warehouse_qty, orderable_qty, brand, type, days_available, shipping_rate, weight, map_protected, map_discount] MATCH: brand=x, warehouse_qty 1, discontinued=True, map_protected=False SET: retail_price = (sug_retail * 0.95), offer_price1 = (cost * 1.25 + shipping_rate) I am looking to allow the merchandising team to have more control over the pricing and formulas - they are afterall technical enough to write excel formulas. I've been looking at writing a desktop application that uses something like numexpr http://code.google.com/p/numexpr/ or http://sympy.org/en/index.html to allow non-programmers to integrate their own logic into our pricing backend. We have multiple price-tiers we have to set, for multiple markets, so an elegant solution is needed. It's getting frustrating for the dev team to continually tweak/manage all of the pricing rules (we sell over 200 brands in 3 markets). My question is; does this seem like a decent approach? Can you think of a better way to parse string-mathematical-grammer? Can you think of a different way for users to provide formula's to integrate into a automated pricing system? Does anyone know of any examples of existing applications that do this? Excel, and Access are out of the question - the volume of data we manipulate has already proven the need to automate it - now we just need some visibility into that automation.

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• Python Pari Library?

  - by silinter

  Pari/GP is an excellent library for functions relating to number theory. The problem is that there doesn't seem to be an up to date wrapper for python anywhere around, (pari-python uses an old version of pari) and I'm wondering if anyone knows of some other library/wrapper that is similar to pari or one that uses pari. I'm aware of SAGE, but it's far too large for my needs. GMPY is excellent as well, but there are some intrinsic pari functions that I miss, and I'd much rather use python than the provided GP environment. NZMATH, mpmath, scipy and sympy were all taken into consideration as well. On a related note, does anyone have any suggestions on loading the pari dll itself and using the functions contained in it? I've tried to very little success, other than loading it and learning about function pointers.

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