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

Hi,

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

Answer 1

[Image Analyst]

Did you try

fitresult = max([0, fitresult]); % bump negative values up to zero.

[CMatlabWold]

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])