bisect.m

来自「several numerical method code」· M 代码 · 共 26 行

function root = bisection(func, xl, xu, es, maxit)
% uses bisection method to find the root of a function
% input:
% func= name of function
% xl, xu = lower and upper guesses
% es = (optional) stopping criterion (%)
% maxit = (optional) maximum allowable iterations
% output:
% root = real root
if feval(func,xl)*feval(func,xu) >0 % if guesses do not bracket a sign
error ('no bracket') % dispaly an error message
return % and terminate
end
% if necessary, assign default values
if nargin<5, maxit = 50; end % if maxit blank set to 50
if nargin<4, es = 0.001; end % if es blank set to 0.001
% bisection
iter = 0;
xr = xl;
while (1)
xrold = xr;
xr = (xl + xu)/2;
iter = iter + 1;
disp(iter); disp(xr) % display calculated result
if xr ~= 0, ea = abs((xr-xrold)/xr)*100; endtest = feval(func,xl)*feval(func,xr);if test < 0xu = xr;elseif test > 0xl = xr;elseea =0;endif ea <= es | iter >= maxit, break, endendroot = xr;