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How to Prevent Lowess 3D Curve From Dipping into Negative Values

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CMatlabWold on 28 Oct 2020
Commented: CMatlabWold on 28 Oct 2020
I have a code. The Z value represents total complaints. When I run the code to get a 3D scatterplot with Lowess curve, the curve dips into negative values. Since it is impossible to have a negative value of complaints, this is a problem for me.
I need the Lowess curve to stay in the positive realm. I'd appreciate any help.
This is my code:
function [fitresult, gof] = createFit1(x, y, z)
ss0 = readtable('StatenIsland3D.xlsx')
x = ss0{:,1}
y= ss0{:,2}
z = ss0{:,3}
[xData, yData, zData] = prepareSurfaceData( x, y, z );
% Set up fittype and options.
ft = fittype( 'lowess' );
% Fit model to data.
[fitresult, gof] = fit( [xData, yData], zData, ft, 'Normalize', 'on' );
% Plot fit with data.
figure( 'Name', 'Staten Island' );
h = plot( fitresult, [xData, yData], zData );
legend( h, 'Staten Island', 'z vs. x, y', 'Location', 'NorthEast', 'Interpreter', 'none' );
% Label axes
xlabel( 'x', 'Interpreter', 'none' );
ylabel( 'y', 'Interpreter', 'none' );
zlabel( 'z', 'Interpreter', 'none' );
grid on

Answers (1)

Image Analyst
Image Analyst on 28 Oct 2020
Did you try
fitresult = max([0, fitresult]); % bump negative values up to zero.
  1 Comment
CMatlabWold on 28 Oct 2020
If I add it under
[fitresult, gof] = fit( [xData, yData], zData, ft, 'Normalize', 'on' );
fitresult = max([0, fitresult])
I get this message:
Error using fittype/horzcat (line 6)
Concatenation of double objects not permitted.
Error in LowessTrial2 (line 17)
fitresult = max([0, fitresult])

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