www.pudn.com > geometric.rar > oncurve.m, change:2004-08-13,size:3139b

function index=oncurve(x,y,xnot,ynot)  % index=oncurve(x,y,xnot,ynot) %  % ONCURVE returns zero if the point (xnot,ynot) is not determined to lie on % the piecewise linear curve represented by the vectors x & y. If % (xnot,ynot) does lie on the curve then the returned value is the index % such that (xnot,ynot) lies between  % (x(index),y(index)) & (x(index+1),y(index+1)).  % (If (xnot,ynot) is exactly equal to a point in (x,y) then index gives % that point. % % G.F. Margrave, December 1993 % % NOTE: It is illegal for you to use this software for a purpose other % than non-profit education or research UNLESS you are employed by a CREWES % Project sponsor. By using this software, you are agreeing to the terms % detailed in this software's Matlab source file.   % BEGIN TERMS OF USE LICENSE % % This SOFTWARE is maintained by the CREWES Project at the Department % of Geology and Geophysics of the University of Calgary, Calgary, % Alberta, Canada.  The copyright and ownership is jointly held by  % its author (identified above) and the CREWES Project.  The CREWES  % project may be contacted via email at:  crewesinfo@crewes.org %  % The term 'SOFTWARE' refers to the Matlab source code, translations to % any other computer language, or object code % % Terms of use of this SOFTWARE % % 1) Use of this SOFTWARE by any for-profit commercial organization is %    expressly forbidden unless said organization is a CREWES Project %    Sponsor. % % 2) A CREWES Project sponsor may use this SOFTWARE under the terms of the  %    CREWES Project Sponsorship agreement. % % 3) A student or employee of a non-profit educational institution may  %    use this SOFTWARE subject to the following terms and conditions: %    - this SOFTWARE is for teaching or research purposes only. %    - this SOFTWARE may be distributed to other students or researchers  %      provided that these license terms are included. %    - reselling the SOFTWARE, or including it or any portion of it, in any %      software that will be resold is expressly forbidden. %    - transfering the SOFTWARE in any form to a commercial firm or any  %      other for-profit organization is expressly forbidden. % % END TERMS OF USE LICENSE it=[]; %t=clock; n=length(x); index=0; % assume false closenough=10*eps;  % test for equality ind= find(x==xnot); if(~isempty(ind)) 	ind2=find(y(ind)==ynot); 	if(~isempty(ind2)) 			index=ind(ind2); 			return; 	end end  % find the points which bracket xnot,ynot indx = surround(x,xnot); indy = surround(y,ynot); %check for a vertical segment  if isempty(x(indy+1)) 	if isempty(x(indy)) 		indx=indy; 	end elseif ~isempty(x(indy+1)) 	if x(indy)==x(indy+1) 		indx=indy; 	end end  for k=1:length(indx) 	it=find(indx(k)==indy); 	if(~isempty(it)) 		itest=indx(k); 		break; 	end end  if(isempty(it)) 	return; end 	 %compute perpedicular distance  if( x(itest)~=x(itest+1) ) 	m=(y(itest+1)-y(itest))./(x(itest+1)-x(itest)); 	b=y(itest)-m.*x(itest);  	dtest=abs(m*xnot-ynot+b)./sqrt(m.*m+1);  else  dtest=abs(xnot-x(itest)); end d=min(dtest); 	 if(d<closenough) 		it=find(d==dtest); 		index=itest(it); 		%etime(clock,t) 		return; end