www.pudn.com > geometric.rar > slope.m, change:2004-08-13,size:2692b


function s=slope(x,y,xnot)  % s=slope(x,y,xnot) % % compute the slope of the curve given by x,y at the point xnot. If the curve % is multivalued, then multiple s's will be returned. If the curve is a polygon, then % it must have its first and last points explicitly equal. The curve is assumed  % piecewise linear. If xnot is exactly equal to a point in x, then the slope  % returned is the average of the segments before and after xnot. % % 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  	ind=find(x==xnot); 	if(isempty(ind)) 		ind=surround(x,xnot); 		s=(y(ind)-y(ind+1))./(x(ind)-x(ind+1)); 	else 			n=length(x); 			% extrapolate ends for end conditions 			m1=(y(2)-y(1))/(x(2)-x(1)); 			x0=x(1)-(x(2)-x(1)); 			y0=y(1)+(x0-x(1))*m1; 			mn=(y(n)-y(n-1))/(x(n)-x(n-1)); 			xn1=x(n)+(x(n)-x(n-1)); 			yn1=y(n)+(xn1-x(n))*mn; 			x=[x0 x xn1];% pad first and last samples for end conditions 			y=[y0 y yn1]; 			ind=ind+1; 			s1=(y(ind)-y(ind+1))./(x(ind)-x(ind+1)); 			s2=(y(ind-1)-y(ind))./(x(ind-1)-x(ind)); 		s=.5*(s1+s2); 	end