Matlab: Errorlinefunction (exponential)

Supplement to errorlines with Matlab

Exponential Fitting

(German) This plot is about the previous post with exponential behavior of the form "b*(exp(a*x)". The structur is the same as in "Errorlines" but it has one further input value.
function [smax,smin,rmax,rmin] = errexpfunc(x,y,xerr,yerr, count,scale)
"Scale" is the position of the interception auf the two functions in dependence of the x-values. The interception is fpr "scale = 0" at the first x-value, "scale = 2" at the last x-value and "scale = 1" in the middle.

source code:

function [smax,smin,rmax,rmin] = errexpfunc(x,y,xerr,yerr, count,scale)
%This is a function to plot a maximal and minimal errorline with given
%errors 'xerr' and 'yerr'. It also can create the box around the mesured
%values to see in which area the errorlines are plotted.
%For count 1 it plots just the errorline. For count 2 it plots the box and
%count 3 it plots both. Scale ist the value, where the intersection of the
%two functions are. It just exsists in the area [0;2).


l=numel(x);
xmid=x(1)+(x(l)-x(1))/2*scale
xerr=0;
if(xerr==0)
   xerr = zeros([l,1])
end
ymax=y+yerr
ymin=y-yerr

fitmax=fit(x,ymax,@(a,b,x) b*exp(a*x));
fitmin=fit(x,ymin,@(a,b,x) b*exp(a*x));
fitVal=fit(x,y, @(a,b,x) b*exp(a*x));
%Fit the maximal and the minimal errorlines through the mesured values with
%their deviations.
a=coeffvalues(fitmax);
b=coeffvalues(fitmin);
c=coeffvalues(fitVal);
amax=a(1);
amin=b(1);
bmax=a(2);
bmin=b(2);
afit=c(1);
bfit=c(2);

%Declare the 4 corners of the box
xlu=x(1)-xerr(1);
xld=x(1)-xerr(1);
xru=x(l)+xerr(1);
xrd=x(l)+xerr(1);

ylu=exp(amax*xlu)*bmax;
yrd=exp(amin*xrd)*bmin;
ymid=exp(afit*xmid)*bfit;

yru=exp(amax*xru)*bmax;
yld=exp(amin*xld)*bmin;
ymid=exp(afit*xmid)*bfit;
xcrnl=[xld xlu];
xcrnr=[xrd xru];
ycrnl=[yld ylu];
ycrnr=[yrd yru];

expmaxx=[xlu xmid xrd];
expmaxy=[ylu ymid yrd];
expminx=[xld xmid xru];
expminy=[yld ymid yru];

fitmax1=fit(expmaxx',expmaxy',@(a,b,x) b*exp(a*x));
fitmin1=fit(expminx',expminy',@(a,b,x) b*exp(a*x));
a=coeffvalues(fitmax1);
b=coeffvalues(fitmin1);
smax=a(1);
smin=b(1);
rmax=a(2);
rmin=b(2);



hold on;
if(count==1)
    h1=plot(fitmax1);
    set(h1,'Color',[0.0 0.7 0.3])
    h2=plot(fitmin1)
    set(h2,'Color',[0.0 0.7 0.3])
    legend([h1],'Errorfunctions');
end
if(count==2)
    h3=plot(fitmax,'--');
    set(h3,'Color',[0.8 0 0.4]);
    h4=plot(fitmin,'--');
    set(h4,'Color',[0.8 0 0.4]);
    plot(xcrnl',ycrnl','--','Color',[0.8 0 0.4]);
    plot(xcrnr',ycrnr','--','Color',[0.8 0 0.4]);
    legend([h4],'Errorbox');
end
if (count==3)
    h1=plot(fitmax1);
    set(h1,'Color',[0.0 0.7 0.3])
    h2=plot(fitmin1)
    set(h2,'Color',[0.0 0.7 0.3])
    h3=plot(fitmax,'--');
    set(h3,'Color',[0.8 0 0.4]);
    h4=plot(fitmin,'--');
    set(h4,'Color',[0.8 0 0.4]);
    plot(xcrnl',ycrnl','--','Color',[0.8 0 0.4]);
    plot(xcrnr',ycrnr','--','Color',[0.8 0 0.4]);
    plot(xcrnl',ycrnl','--','Color',[0.8 0 0.4]);
    plot(xcrnr',ycrnr','--','Color',[0.8 0 0.4]);
    legend([h1 h4],'Errorfunctions','Errorbox');
end

end