steporback.m

高斯迭代加速收敛计算非线性规划高斯迭代加速收敛计算非线性规划

function [a,b]=StepOrBack(FUN,x1,h0,flag)
h=h0;
y1=feval(FUN,x1);
x2=x1+h;
y2=feval(FUN,x2);
if y2>=y1
h=-h;
x3=x1;
y3=y1;
x1=x2;
y1=y2;
x2=x3;
y2=y3;
end
h=2*h;
x3=x2+h;
y3=feval(FUN,x3);
while y2>=y3
x1=x2;
y1=y2;
x2=x3;
y2=y3;
h=2*h;
x3=x2+h;
y3=feval(FUN,x3);
end
if h<0
a=x3;
b=x1;
else
a=x1;
b=x3;
end
% all the lines below are designed to show whether the root range result of the specified
% function is right or no
% which means all lines below you can delete them all
% frmluck 2007,10,8
if flag
x0=a:abs(0.1*h):b;
[m,n]=size(x0);
for i=1:n
y0(i)=feval(FUN,x0(i));
end
str=sprintf('range of single root [%.4f,%.4f] and step=%.2f',a,b,h);
plot(x0,y0,'LineWidth',2);
title(str)
grid on
end