function [a,b]=areafind(t0,h,c)
%利用進退法求出，調用函數為g,t0為初始值，h為步長,c為步長的系數
a=t0;
b=t0+h;

while 1
    
    if g(a)<g(b)
        h=h*c;
        a=a-h;
        b=a+h;
        
        if g(b)<g(b+h/c) && g(b)<g(a) 
            b=b+h/c;
            break;
        end
        
    else
       
        a=b;
        h=h*c;
        b=a+h;
        
        if g(a)<g(b) && g(a)<g(a-h/c) 
           a=a-h/c;
           break;
        end

    end
end