a=load('d:\shuju\X90D4.dat','r');
y=a(10:1000);
n=length(y)
N=5*n+45;
x1=[50:5:N];
x=x1';
b=length(x)
plot(x,y,'g');
pcoef=polyfit(x,y,30)
xx=50:N; 
yy=polyval(pcoef,xx); 
plot(x,y,'g',xx,yy,'r') ;