Fitting nonlinear model to data

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Sonisa 2018-9-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417651-fitting-nonlinear-model-to-data

评论： Sonisa 2018-9-5

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I have been trying to fit nonlinear model to my data

Here are the codes:

X = [0.05 0.06 0.07 0.08 0.09 0.1 0.125 0.15 0.175 0.2 0.25 0.3 0.4 0.5 0.6 0.7 0.8 -0.1 -0.5 -0.8];%FAW40;
Y = [0.3 0.4 0.35 0.42 0.3 0.32 0.35 0.37 0.38 0.495 0.45 0.55 0.6 0.55 0.6 0.6 0.65 0.2 0.3 0.5]; %NDVI;
figure
% plot(FAW40_GS,NDVI_GS,'ok');
k = diff(x)<0; %select only data when the soil is drying
x = X(1:end,:);
y = Y(2:end,:);
plot(x(k(:,1),1),y(k(:,1),1),'ok')
hold all
plot(x(k(:,2),2),y(k(:,2),2),'+k')
plot(x(k(:,3),3),y(k(:,3),3),'dk')
set(gca,'XLim',[0 1])
set(gca,'XTick',(0:0.1:1))
%set(gca,'YLim',[0 1])
set(gca,'YTick',(0:0.1:1));
hold all
ylabel('\bf NDVI','fontsize',14);
xlabel('\bf FAW','fontsize',14);
slope = 0.2;
r = 0.40;
ypred = @(A, x)(A(1) ./ (A(2) + exp([(r-Y)*slope])));
A0 = [0.2;-0.5];
A1 = [ 0.3; -0.2];
opts = statset('nlinfit');
opts.RobustWgtFun = 'bisquare';
A_fit = nlinfit(x,y,ypred,A0,A1,opts);
hold all
plot(x',y','ko', x,ypred(A_fit,x'))
legend('Data','Fitted','location', 'northwest')
 _But when I did I get the error 
Error using nlinfit (line 185)
Requires a vector second input argument. Any help would be appreaciated.
 _

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Matt J 2018-9-5

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Nope. Those lines will not execute

>> x = 0.637259937  0.621294757  0.672668532 0.521265646  0.421903196  0.549649009 0.312588087 0.28327584  0.359424364 0.253502479  0.253985122  0.313290724 0.209563459  0.2319699  0.274603618 0.156334057  0.183523167  0.236265826 0.475258711  0.560432822  0.629973282 0.238506777  0.253712482 0.302720237
 x = 0.637259937  0.621294757  0.672668532 0.521265646  0.421903196  0.549649009 0.312588087 0.28327584  0.359424364 0.253502479  0.253985122  0.313290724 0.209563459  0.2319699  0.274603618 0.156334057  0.183523167  0.236265826 0.475258711  0.560432822  0.629973282 0.238506777  0.253712482 0.302720237
                 ↑
Error: Invalid expression. Check for missing multiplication operator, missing or unbalanced
delimiters, or other syntax error. To construct matrices, use brackets instead of
parentheses.