warning in Polyval - Warning: Matrix is singular, close to singular or badly scaled. Results may be inaccurate. RCOND = NaN.

Hi everybody.. I am having the following warning using polyval

It happens after I delete negative values from a dataset since before this cleaning it worked.

% TOLGO I VALORI NEGATIVI
% Creo un array di indici logici che indica quali righe hanno almeno un valore negativo
idx_neg = any(rawData < 0, 2);

cleanData = rawData;
% Elimino le righe selezionate
cleanData(idx_neg, :) = [];
pressureIN = cleanData(:,1);
pressureOUT= cleanData(:,2);
flowrate = cleanData(:,3);

PHeadLoss = pressureIN - pressureOUT;



%DATA
figure('Name',' PRESSURE HEAD LOSS vs FLOWRATE')
plot(flowrate, PHeadLoss, '*k');
title('Pressure Head Loss vs FLOW RATE');
xlabel('flow rate');
ylabel('P Head Loss');
hold on
%densityplot(flowrate, PHeadLoss, [50,50]);

[p, S, mu] = polyfit(flowrate, PHeadLoss, 2)

[y,delta] = polyval(p,flowrate,S,mu);

%LINEAR FIT
plot(flowrate, y, 'r-');
%hold on

% Linear Fit of Data with 95% Prediction Interval
%plot(flowrate,y+2*delta,'m--',flowrate,y-2*delta,'m--')
title('Pressure Head Loss vs FLOW RATE');
xlabel('flow rate');
ylabel('P Head Loss');

while the watning is:

p =

NaN NaN NaN

S =

struct with fields:

R: [3×3 double]

df: 751629

normr: NaN

mu =

NaN

NaN

Warning: Matrix is singular, close to singular or badly scaled.

Results may be inaccurate. RCOND = NaN.

> In polyval (line 109)

Thanks in advance!

[VBBV]

Maybe there's text in data being read. Can you share the data file?

Answer 1

[Bruno Luong]

Check your data with this command

all(isfinite(rawData(:)))

if it returns 0/false then your data is not valid