polyfit at 74 how can I improve results?

     Type of error coming how can I make good results warning(message('MATLAB:polyfit:RepeatedPoints'));

In polyfit at 74 Warning: Polynomial is badly conditioned. Add points with distinct X values or reduce the degree of the polynomial.

I am using this 
[p S mu]= polyfit(x1(1:xxx),y2,3);

Answer 1

[Image Analyst]

Do you have some x1 values that are repeated? What does this say

length(unique(x1(1:xxx)) - length(x1(1:xxx))  % No semicolon

[RS]

1 is answer

[Image Analyst]

Can't be 1, must be -1 because you can never have more unique values than original values. So, this is as I thought. One of the x values is repeated, meaning that you have two different y values for the same x value and thus the "curve" would have to be perfectly vertical at that location. That is not allowed. Do something to resolve that "step" in your data and it should then be okay.

[RS]

every time I am doing fitting it is not coming -1 how can I do? some time it is coming some positive numbers.