ReZero's Utopia.

# Sympy 解方程

Word count: 308Reading time: 1 min
2017/02/08 Share
1. 解普通方程

``````from sympy import *
x = Symbol('x')
y = Symbol('y')
print solve([2 * x - y - 3, 3 * x + y - 7],[x, y])``````
``````* * *

![test](http://img.blog.csdn.net/20170208213138869?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZ2l0aHViXzM1OTU3MTg4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)

* * *``````
1. 解微积分

``````from sympy import *
n = Symbol('n')
s = ((n+3)/(n+2))**n

#无穷为两个小写o

print limit(s, x, oo)``````
2. 求定积分

``````from sympy import *
t = Symbol('t')
x = Symbol('x')
m = integrate(sin(t)/(pi-t),(t,0,x))
n = integrate(m,(x,0,pi))
print n``````

3. 解微分方程

``````#y' = 2xy  的通解

from sympy import *
f = Function('f')
x = Symbol('x')
print dsolve(diff(f(x),x) - 2*f(x)*x,f(x))

#说明：

f = Function('f')
x = Symbol('x')

#表示f(x)的导：

diff(f(x), x, index)
>>> diff(sin(x), x, 1)
cos(x)

dsolve(eq, f(x))
#第一个参数为微分方程（要先将等式移项为右端为0的形式)
#第二个参数为要解的函数(在微分方程中)``````
1. 矩阵化简

``````from sympy import *
x1,x2,x3 = symbols('x1 x2 x3')
a11,a12,a13,a22,a23,a33 = symbols('a11 a12 a13 a22 a23 a33')
m = Matrix([[x1,x2,x3]])
n = Matrix([[a11,a12,a13],[a12,a22,a23],[a13,a23,a33]])
v = Matrix([[x1],[x2],[x3]])
f = m * n * v
f[0] 化简， subs代入计算
print f[0].subs({x1:1, x2:1, x3:1})``````

Author：ReZero

CATALOG