trendline.m

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% trendline computation
% (not optimised)
%
% Matlab 7 Release 14 SP2

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  Property of Freescale
%  Freescale Confidential Proprietary
%  Freescale Copyright (C) 2005 All rights reserved
%  ----------------------------------------------------------------------------
%  $RCSfile: trendline.m.rca $
%  $Revision: 1.4 $
%  $Date: Thu Dec 14 14:15:16 2006 $
%  Target: Matlab
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

function [y4,xS]=trendline(x,y,N,step,xSMax)
if nargin==3
    xSMax = max(x);
end
xSMax = max(xSMax,max(x));
xS=[min(x):step:xSMax];
y2=log10(y);
warning off all 
coeff=polyfit(x,y2,N);
y3 = zeros(size(xS,1),size(xS,2));
y3_2 = zeros(size(x,1),size(x,2));
for i=1:N+1
    temp = (xS.^(N+1-i))*coeff(i);
    y3 = y3 + temp;
    temp2 = (x.^(N+1-i))*coeff(i);
    y3_2 = y3_2 + temp2;
end
y4 = pow2(y3*log2(10));
warning on all