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微分方程笔记

时间:2014-05-14 08:52:13      阅读:314      评论:0      收藏:0      [点我收藏+]

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线性常微分方程解法


一阶线性微分方程

dybubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣+P(x)y=Q(x)bubuko.com,布布扣
对应的齐次线性方程
dybubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣+P(x)y=0bubuko.com,布布扣
此齐次方程可以用分离变量法求得通解: y=Cebubuko.com,布布扣?P(x)dxbubuko.com,布布扣bubuko.com,布布扣

常数变易法求非齐次线性方程的通解:
将齐次方程的通解中的C换成u(x): y=uebubuko.com,布布扣?P(x)dxbubuko.com,布布扣bubuko.com,布布扣 带入非齐次线性方程,可求得其解为:
y=Cebubuko.com,布布扣?P(x)dxbubuko.com,布布扣+ebubuko.com,布布扣?P(x)dxbubuko.com,布布扣Q(x)ebubuko.com,布布扣P(x)dxbubuko.com,布布扣dxbubuko.com,布布扣
即非齐次线性方程的通解等于对应的齐次方程的通解加非齐次方程的一个特解

二 伯努利方程

dybubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣+P(x)y=Q(x)ybubuko.com,布布扣nbubuko.com,布布扣bubuko.com,布布扣
可变换为一阶线性微分方程:
z=ybubuko.com,布布扣1?nbubuko.com,布布扣bubuko.com,布布扣 ,可化为:
dzbubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣+(1?n)P(x)z=(1?n)Q(x)bubuko.com,布布扣

三 可降阶的高阶微分方程

1)
ybubuko.com,布布扣(n)bubuko.com,布布扣=f(x)bubuko.com,布布扣
两边积分,可降为n-1阶的微分方程
ybubuko.com,布布扣(n?1)bubuko.com,布布扣=f(x)dx+Cbubuko.com,布布扣1bubuko.com,布布扣bubuko.com,布布扣
连续n次积分,可得方程含有n个任意常数的通解
2)
ybubuko.com,布布扣′′bubuko.com,布布扣=f(x,ybubuko.com,布布扣bubuko.com,布布扣)bubuko.com,布布扣
ybubuko.com,布布扣bubuko.com,布布扣=pbubuko.com,布布扣 ,则ybubuko.com,布布扣′′bubuko.com,布布扣=pbubuko.com,布布扣bubuko.com,布布扣bubuko.com,布布扣 , 原方程变换为关于变量x,p的一阶微分方程
pbubuko.com,布布扣bubuko.com,布布扣=f(x,p)bubuko.com,布布扣
其通解为
dybubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣=φ(x,Cbubuko.com,布布扣1bubuko.com,布布扣bubuko.com,布布扣
积分可得原方程通解:
y=φ(x,Cbubuko.com,布布扣1bubuko.com,布布扣)dx+Cbubuko.com,布布扣2bubuko.com,布布扣bubuko.com,布布扣
3)
ybubuko.com,布布扣′′bubuko.com,布布扣=f(y,ybubuko.com,布布扣bubuko.com,布布扣)bubuko.com,布布扣
(方程中不含自变量x的显式)
ybubuko.com,布布扣bubuko.com,布布扣=pbubuko.com,布布扣 , 有
ybubuko.com,布布扣′′bubuko.com,布布扣=dpbubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣=dpbubuko.com,布布扣dybubuko.com,布布扣bubuko.com,布布扣 dybubuko.com,布布扣dxbubuko.com,布布扣bubuko.com,布布扣=pdpbubuko.com,布布扣dybubuko.com,布布扣bubuko.com,布布扣bubuko.com,布布扣
原方程化为:
pdpbubuko.com,布布扣dybubuko.com,布布扣bubuko.com,布布扣=f(y,p)bubuko.com,布布扣
其通解为
ybubuko.com,布布扣bubuko.com,布布扣=p=φ(y,Cbubuko.com,布布扣1bubuko.com,布布扣)bubuko.com,布布扣
分离变量并积分可得原方程的通解:
dybubuko.com,布布扣φ(y,Cbubuko.com,布布扣1bubuko.com,布布扣)bubuko.com,布布扣bubuko.com,布布扣=x+Cbubuko.com,布布扣2bubuko.com,布布扣bubuko.com,布布扣






微分方程笔记,布布扣,bubuko.com

微分方程笔记

标签:style   class   c   ext   color   http   

原文地址:http://www.cnblogs.com/crossmind/p/3725560.html

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