Error says "Subscript indices must either be real positive integers or logicals"

x  = [1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 9, 8, 7, 6, 5, 4, 3, 2, 1]; 
n  = -9:9; 
x1 = 5*x(n-2) - 3*x(n+4) 

Array indices must be positive integers or logical values.

How to remove this error?

[Sam Chak]

What is variable n? It seems that n indicates the relative position (left and right) from the mean of the data set x, which is an array. In array indexing in MATLAB, the sequential position are assigned as positive integers that begins from 1 (Python indexing starts at 0). This is the Rule in MATLAB.

So, you need to play with a little bit of arithmetics in your head, just as shown by bhai @Arun.

Answer 1

[Arun]

Hey,

here, the variable 'x' has index values ranging from 1 to 19. So to remove the error keep the index value with in that range of 1 to 19. For n-2 and n+4 both to be in range 1 to 19 the supported value for are in range 3 to 15. You can use the following code:

x = [1,2,3,4,5,6,7,8,9,9,9,8,7,6,5,4,3,2,1];
n = 3:15;
x1 = 5 * x(n-2) - 3*x(n+4)

x1 = 1×13

-16 -14 -12 -7 -2 6 14 22 30 33 36 34 32

another workaround can be to restructure the equation with respect to the size of 'x', one possible way is:

x = [1,2,3,4,5,6,7,8,9,9,9,8,7,6,5,4,3,2,1];
n = -9:9;
n = n + 10;
x1 = 5 * x(n)-2 - 3*x(n)+4

x1 = 1×19

4 6 8 10 12 14 16 18 20 20 20 18 16 14 12 10 8 6 4

Hope this gives you an idea to proceed.