function x=chase (a,b,c,f)

 % the method of chaase*******************************

 %  a, b, c,分别是是方程组的下对角，主对角，上对角的三条

 %  alpha，beta， gama分别是Crout分解的主和次对角线

 %    /beta(1)    0    ...             ...        0  0     \

 %    |alpha(2)   beta(2)  ...          ...       0  0     |

 %  L=|0          alpha(3) ...beta(3)                      |

 %    |                                                    |

 %    |                                                    |

 %    \                                   alpha(3) beta(n) /

 %********************************************************

 beta(1)=b(1);gama(1)=c(1)/beta(1);y(1)=f(1)/beta(1);

 for i=2:length(b)

 alpha(i-1)=a(i-1);beta(i)=b(i)-alpha(i-1)*gama(i-1);

 if i<=length(b)-1

     gama(i)=c(i)/beta(i);

 end

 y(i)=(f(i)-alpha(i-1)*y(i-1))/beta(i);

 end

 x(length(b))=y(length(b));

 for i=length(b)-1:-1:1

 x(i)=y(i)-gama(i)*x(i+1);

 end