makedist 'PiecewiseLinear'

The code below is almost verbatim from the Matlab documentation regarding the use of makedist with 'PiecewiseLinear'. It works as expected.

clear
load hospital
[f,x] = ecdf(hospital.Weight)
f2 = f(1:5:end); % keep a less dense grid of points
x2 = x(1:5:end);

fig1=figure;
hold on
pd3 = makedist('PiecewiseLinear','x',x2,'Fx',f2)
hist = pdf(pd3,x);
stairs(x,hist)

With a very minor modificaiton, the 'PiecewiseLinear' command throws and error.

clear
load hospital
[f,x] = ecdf(hospital.Weight)
f2 = f(1:1:end); % keep the original grid of points
x2 = x(1:1:end);

fig1=figure;
hold on
pd3 = makedist('PiecewiseLinear','x',x2,'Fx',f2)
hist = pdf(pd3,x);
stairs(x,hist)

The error is

Error using prob.PiecewiseLinearDistribution>checkParams (line 226)
X must be a row vector of at least two sorted real values.

Error in prob.PiecewiseLinearDistribution (line 98)
            checkParams(x,Fx);..........

I am deeply confused as to why it would suddenly throw an error. The vectors x2 and f2 seem to meet the criteria for appropriate input.

Any help would be appreciated.

Answer 1

[Harsha Priya Daggubati]

Hi,

Your vector X has to be strictly increasing (X1<X2). I can see X(1) and X(2) are equal to 111. This is causing the issue.

Hope this helps!