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