c4_3.m

这是我从一本基于MATLAB实现的数值分析算法的书中自带的光盘程序

%C4_3.m
%用改进的试位法求f(x)=0的根
function C4_3
a=input('Lower bound:a?');
b=input('Upper bound:b?');
ep=input('Tolerance:ep?');
it_limit=input('Iteration limit?');
 y_a=func3(a);
 y_b=func3(b);
 IT=0;
 KL=0;
 KR=0;
 s=abs(y_b-y_a);
 fprintf('It,     a,      c,       b,       f(a),      f(b),      abs(f(a)-f(b)) \n');
 while s>ep
    IT=IT+1;
    if IT>it_limit break;end
    if y_a*y_b>0
       fprintf('无根！'); 
    else
       c=a-((b-a)/(y_b-y_a))*y_a;
       y_c=func3(c);
       aa=a; 
       y_aa=y_a;
       bb=b;
       y_bb=y_b;
       if y_a*y_c<0
          b=c;
          y_b=y_c;
          KL=KL+1;
          if KL>0 
             y_a=y_a/2;
          end
       else
           a=c;
           y_a=y_c;
           KR=KR+1;
           if KR>0
              y_b=(y_b)/2;
           end
       end
    end
    s=abs(y_b-y_a);
    fprintf('%1d,  %6.5f,  %6.5f,  %6.5f,  %6.5f,  %6.5f,  %6.5e \n',IT,aa,c,bb,y_aa,y_bb,abs(y_a-y_b)); 
 end