function y=find_bound_converge(f,d,signum,firststep,i,varargin); % FIND_BOUND_CONVERGE(f,d,signum,firststep,i,varargin); % f is a string that contains the name of the function % d is a string and must be either 'right' or 'left' % if d='right', then the function will be evaluated at values that % approach the limit value from the right (values of argument becoming smaller) % if d='left', then the function will be evaluated at values that % approach the limit value from the left(values of argument becoming larger) % signum can take the values -1,0,1 and NaN, and the routine stops % once the function takes a value with sign equal to signum % firststep is the amount added/subtracted in the first iteration, % the value added/subtracted at iteration n being 0.5^(n-1)*firststep % the function f is allowed to have more than one argument, and % i is the position of the argument for which convergence occurs % varargin gives the limit values for all the arguments of f if strcmpi(d,'right') x=firststep; elseif strcmpi(d,'left') x=-firststep; else error('Direction must be either right or left!'); end found_boundary=0; n=length(varargin); start_value=varargin{i}; if isnan(signum) while (found_boundary==0) x=0.5*x; varargin{i}=start_value+x; fvalue=feval(f,varargin{1:n}); if isnan(fvalue) found_boundary=1; y=start_value+x; end end else while (found_boundary==0) x=0.5*x; varargin{i}=start_value+x; fvalue=feval(f,varargin{1:n}); if (sign(fvalue)==signum) found_boundary=1; y=start_value+x; end end end