MATLAB: Hi, I have a question about displaying the line limit for p-chart. The line always displayed in y=0.

control chartp-chartstatistical process control

clear all
close all
clc
n=xlsread('statTest.xls',5,'C2:C51'); % sample size set 
p=xlsread('statTest.xls',5,'D2:D51'); % probability of having the non-confirming units
pAverage=(sum(p))/(sum(n)); % average probability of defects
% construct the p-chart

n=50;
c=1;
while c<=50;
    CL(c)=pAverage; % centraline vector
    LCL(c)=pAverage-3*((pAverage*(1-pAverage)/n)^(0.5)); % upper control limit vector
      UCL(c)=pAverage+3*((pAverage*(1-pAverage)/n)^(0.5)); % lower control limit vector
      si1(c)=CL(c)+((UCL(c)- CL(c))/3);
      si2(c)=si1(c)+((UCL(c)- CL(c))/3);
      si3(c)=CL(c)-(CL(c)/3);
      si4(c)=si3(c)-(CL(c)/3);
      if LCL(c)<0; % lower control limit can not be negative
          LCL(c)=0;
      end
      c=c+1;
  end
% construct the time vector
t=1:50; 
% construct the p-chart
figure
plot(t,UCL,'k--',t,si1,'m:',t,si2,'g:', t,CL,'-',t,si3,'m:',t,si4,'g:', t,LCL,'k--',t, p,'*:'); hold on
legend('UCL','1Sigma','2Sigma','CL','1Sigma','2Sigma','LCL')
xlabel('defects')
ylabel('c')

Best Answer

Probabilities are between 0 and 1. When you plot a value between 0 and 1 on a plot that goes up to 450, the value is going to be squished near the y axes.
Related Question