Why do I get "Array indices must be positive integers or logical values"

Very new at matlab, i'm trying to fit linear function to a set of values. I keep getting "Array indices must be positive integers or logical values"

Please advise.

x = [62857 63320 63202 64754 64109 64298]'; % Population 
y = [16366669 16864938 17087795 17224537 17301839 17095073]'; % Ridership
n = numel(y); % number of points being fitted
plot(x,y, '+')
 
A = [ones(6,1), x]; % design matrix 
m = size(A,2); %  parameters that we want fitted
b = A \ y;
f(x) = b(1) + b(2) *x;
xi = linspace(0,100);
fxi = f(xi);
plot(x, y, '+', xi, fxi)

Answer 1

[Mauro Fusco]

Arrays in Matlab are indexed starting from 1. Just replace xi = linspace(0,100); with

xi = linspace(1,100);

and it will not give error.

[maria serey-roman]

Thank you, that worked!

[Walter Roberson]

This deals with the problem accidentally, and does not solve the real issue.

Answer 2

[Walter Roberson]

Please read https://www.mathworks.com/matlabcentral/answers/453477-error-array-indices-must-have-positive-or-logical-values#answer_368263 : you are confusing formula and expressions.

Also, your x range is about 60000, but the range over which you plot the projected line is 0 to 100.

plot(x, y, '+', x, polyval(flipud(b), x))