问题
I want to solve a set of equations, linear, or sometimes quadratic. I don't have a specific problem, but often, I have been in this situation often.
It is simple to use wolframalpha.com, the web equivalent of Mathematica, to solve them. But that doesn't provide the comfort and convenience of an iPython shell.
Is there a simple library to work on linear and quadratic equations from a python shell?
Personally, I find it extremely convenient to use the Casio 991 MS scientific calculator. I know how to set variables, solve equations, and do a lot. I want such a tool preferably usable from within an ipython shell. I am surprised not to have found any. I'm not impressed enough by sage; perhaps I am missing something.
回答1:
sympy is exactly what you're looking for.
回答2:
You discount the best answer as unacceptable.
Your question is "I want a free Computer Algebra System that I can use in Python."
The answer is "SAGE does that."
Have you looked at maxima/macsyma? SAGE provides bindings for it, and that's one of the more powerful free ones.
http://maxima.sourceforge.net/
回答3:
Here is how to solve your original question using Python (via Sage). This basically clarifies the remark Paul McMillan makes above.
sage: a,b,c = var('a,b,c')
sage: solve([a+b+c==1000, a^2+b^2==c^2], a,b,c)
[[a == 1000*(r1 + sqrt(r1^2 + 2000*r1 - 1000000))/(r1 + sqrt(r1^2 + 2000*r1 - 1000000) + 1000), b == -1/2*r1 - 1/2*sqrt(r1^2 + 2000*r1 - 1000000) + 500, c == r1], [a == 1000*(r2 - sqrt(r2^2 + 2000*r2 - 1000000))/(r2 - sqrt(r2^2 + 2000*r2 - 1000000) + 1000), b == -1/2*r2 + 1/2*sqrt(r2^2 + 2000*r2 - 1000000) + 500, c == r2]]
回答4:
For inexact solutions, read up on linear programming and sequential quadratic optimization, then search for Python libraries that performs such optimizations for you.
If the equations require integer solutions, you should search for Diophantine equation solvers for Python.
Just note that using a simple solver for Project Euler is missing the point. The fun, and educational part, is learning how to solve it yourself using primitive methods!
回答5:
Have you looked at SciPy?
It has an example in the tutorials on solving linear algebra:
http://docs.scipy.org/doc/scipy/reference/tutorial/linalg.html#solving-linear-system
回答6:
A free web-service for solving large-scale systems of nonlinear equations (1 million+) is APMonitor.com. There is a browser interface and an API to Python / MATLAB. The API to Python is a single script (apm.py) that is available for download from the apmonitor.com homepage. Once the script is loaded into a Python code, it gives the ability to solve problems of:
- Nonlinear equations
- Differential and algebraic equations
- Least squares model fitting
- Moving horizon estimation
- Nonlinear model predictive control
- etc.
For the new user, the APM Python software has a Google Groups forum where a user can post questions. There are bi-weekly webinars that showcase optimization problems in operations research and engineering.
Below is an example of an optimization problem (hs71.apm).
Model
Variables
x[1] = 1, >=1, <=5
x[2] = 5, >=1, <=5
x[3] = 5, >=1, <=5
x[4] = 1, >=1, <=5
End Variables
Equations
x[1] * x[2] * x[3] * x[4] > 25
x[1]^2 + x[2]^2 + x[3]^2 + x[4]^2 = 40
minimize x[1] * x[4] * (x[1]+x[2]+x[3]) + x[3]
End Equations
End Model
The optimization problem is solved with the following Python script:
# Import
from apm import *
# Select server
server = 'http://xps.apmonitor.com'
# Application name
app = 'eqn'
# Clear previous application
apm(server,app,'clear all')
# Load model file
apm_load(server,app,'hs71.apm')
# Option to select solver (1=APOPT, 2=BPOPT, 3=IPOPT)
apm_option(server,app,'nlc.solver',3)
# Solve on APM server
solver_output = apm(server,app,'solve')
# Display solver output
print solver_output
# Retrieve results
results = apm_sol(server,app)
# Display results
print '--- Results of the Optimization Problem ---'
print results
# Display Results in Web Viewer
url = apm_var(server,app)
print "Opened Web Viewer: " + url
回答7:
For reference: Wolfram Alpha's solution:
a-1000!=0, b = (1000 (a-500))/(a-1000), c = (-a^2+1000 a-500000)/(a-1000)
In python, using sympy's solver module (note that it assumes all equations are set equal to zero):
>>> import sympy
>>> a, b, c = sympy.symbols('a, b, c')
>>> sympy.solve([a + b + c - 1000, a**2 + b**2 - c**2], b, c)
[(1000*(a - 500)/(a - 1000), (-a**2 + 1000*a - 500000)/(a - 1000))]
And of course, a != 1000, as a-1000 is the denominator of the two equations.
回答8:
I have just started using GNU Scientific Library, which however is C library. Looks like there are Python bindings too. So, it might be worth looking at.
回答9:
I'd use Octave for this but I agree, the syntax of Octave isn't what I'd call thrilling (and the docs always confuse me more than they help, too).
回答10:
I don't think there is a unified way of dealing with both linear and quadratic (or generally nonlinear) equations simultaneously. With linear systems, python has bindings to linear algebra and matrix packages. Nonlinear problems tend to be solved on a case by case basis.
回答11:
It depends on your needs:
If you want an interactive graphical interface, then sage is probably the best solution.
If you want to avoid using a graphical interface, but you still want to do computer algebra, then sympy or maxima may cover your needs. (sympy looks very promising, but it still have a long way to go before they can replace mathematica).
If you don't really need symbolic algrebra, but you need a way to program with matrices, solve differential equations, and minimize functions, then scipy or octave are excelent starting points.
回答12:
Take a look at this:
http://openopt.org/FuncDesignerDoc#Solving_systems_of_nonlinear_equations
It is extremely easy to use and quite powerful
回答13:
Well, I just googled into this page by accident. I see many suggestions regarding this and that software tool, but does any tool actually provide an answer? The actual answer is:
[a,b,c] = [200,375,425]
How did I get this? By writing a quick program in the Maxima programming language to find it via "brute force" searching. It only took about 10 minutes to write, seeing as how I'm familiar with the Maxima language. It took a few seconds for the program to run. Here is the program:
euler_solve():= block ( [ a, b, A, B, end:1000],
for a thru end do
(
for b thru end do
(
c: 1000 -a -b,
if c < 0 then
b:end
else if a^2 + b^2 = c^2 then
(
A:a,
B:b,
a:end,
b:end
)
)
),
return( [A,B,c])
);
You can just cut and paste the above code into the wxMaxima user interface, which I run under Ubuntu and not MS Windows. Then you just enter the function name: euler_solve(), hit return, wait a few seconds, and out pops the answer. This particular kind of problem is so simple that you could use any general-purpose programming language to do the search.
回答14:
Try applying Bisection method in py to find the root given an interval:
def f(x, rhs): # f(x) = e^x
return math.e ** x - rhs # e^x = rhs -> e^x - rhs = 0
def solve(rhs, a = 0, b = 100, tol = 1e-3):
while True:
c = (a + b) / 2.0
if(f(a, rhs) * f(c, rhs) > 0):
a = c
else:
b = c
if(abs(f(c, rhs)) < tol):
break
return c
y = math.e ** 3.75 # x = 3.75
print(solve(y)) # 3.7499..
回答15:
On second thoughts, I went through sage in detail and clearly it is the best math free software available.
Just some of the different python math related libraries, it integrates is absolutely awesome.
Mathematics packages contained in Sage:
Algebra GAP, Maxima, Singular
Algebraic Geometry Singular
Arbitrary Precision
Arithmetic GMP, MPFR, MPFI, NTL
Arithmetic Geometry PARI, NTL,
mwrank, ecm Calculus Maxima, SymPy,
GiNaC Combinatorics Symmetrica,
Sage-Combinat Linear Algebra Linbox,
IML Graph Theory NetworkX Group
Theory GAP Numerical
computation GSL, SciPy, NumPy,
ATLAS
Other packages contained in Sage:
Command line IPython Database ZODB,
Python Pickles, SQLite Graphical
Interface Sage Notebook, jsmath
Graphics Matplotlib, Tachyon3d, GD,
Jmol Interactive
programming language Python
Networking Twisted
来源：https://stackoverflow.com/questions/1642357/simplest-way-to-solve-mathematical-equations-in-python