MATLAB: Changing variable value based off x/y location of a product

variables

I've written some code to monitor a mock retail outlet which loads product location (x/y) data from a .xls file and plots it on top the stores blueprint.
the blueprint has defined payment and exit areas, and each product has a payment status variable (P#pay) where 0 = unpaid and 1 = paid. If the product enters the payment area the paystatus variable changes from 0 to 1. I wrote a for/if statement to handle this operation but it's not working properly and I cant seem to figure out why. Below is the code, and thanks for taking the time to look this over!
% Blank, Jacob
clear all
close all
clc
%define store dimensions blueprint
    hold on
    rectangle('position',[0,0,120,110])
%define shelving units
    rectangle('position',[15,20,10,75],'facecolor','y')
    rectangle('position',[35,20,10,75],'facecolor','y')
    rectangle('position',[55,20,10,75],'facecolor','y')
    rectangle('position',[75,10,10,30],'facecolor','y')
    rectangle('position',[90,10,10,30],'facecolor','y')
    rectangle('position',[105,10,10,30],'facecolor','y')
%define freezer space
    rectangle('position',[75,75,40,15],'facecolor','c')
    rectangle('position',[75,50,40,15],'facecolor','c')
%define payment portal
    rectangle('position',[15,0,20,10],'facecolor','g')
    text(21,5,'PAY')
    payYlimMax=10;
    payYlimMin=0;
    payXlimMax=35;
    payXlimMin=15;
%define exit
    rectangle('position',[0,0,15,10],'facecolor','r')
    text(2,5,'EXT')
    extYlimMax=10;
    extYlimMin=0;
    extXlimMax=15;
    extXlimMin=0;
    axis on
%product 1 location data
    P1 = xlsread('location_data','Product 1');
    n=size(P1,1);
    P1X=P1(2:n,1);
    P1Y=P1(2:n,2);
    plot(P1X,P1Y,'ko');
%product 1 payment status  
    P1pay=0;
    for i=1:n-1
        if payXlimMin < P1X(i) < payXlimMax && payYlimMin < P1Y(i) < payYlimMax
            P1pay = 1;
        end
    end   
%product 2 location data
    P2 = xlsread('location_data','Product 2');
    n2=size(P2,1);
    P2X=P2(2:n2,1);
    P2Y=P2(2:n2,2);
    plot(P2X,P2Y,'ko');
%product 2 payment status  
    P2pay=0;
    for i2=1:n2-1
        if payXlimMin < P2X(i2) < payXlimMax && payYlimMin < P2Y(i2) < payYlimMax
            P2pay = 1
        end
    end      
    hold off

Best Answer

" When you write "a<b<c" as you have, it can give you very unexpected results. Very likely you want it to mean "a is less than b and b is less than c", but that is not how matlab interprets it. It groups things this way: (a<b)<c and first determines whether a<b is true or false. Then since (a<b) looks to matlab as though it were a numerical quantity because it occurs in another inequality, it converts the true/false state to a 1 or 0, respectively, and determines whether that 1 or 0 is numerically less than c. This is very far from what you undoubtedly had in mind.
Always write (a<b)&(b<c) and never a<b<c to avoid catastrophes like this.
Roger Stafford "
^answer http://www.mathworks.com/matlabcentral/newsreader/view_thread/317738
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