how can i solve it

i=1:100;
vx_1(i)=(X1(i)-X1((i)-1))/(t(i)-t((i)-1));          % In general
vx_1(1)= (X1(1)-X1(N-1))/(t(N)-t(N-1));             % for i=1

I get the error: Array indices must be positive integers or logical values.

How can I solve it

it works well when you put i= single digit but does not work for array? eg it works well when i=6

[Rik]

http://web.archive.org/web/20210822105224/https://www.mathworks.com/matlabcentral/answers/1435977-how-can-i-solve-it

Answer 1

[Walter Roberson]

When i is 1 then i-1 is 0, and you would be referring to X1(0) and t(0) .

MATLAB cannot use index 0.

See my discussion in https://www.mathworks.com/matlabcentral/answers/1413192-z-must-be-a-matrix-not-a-scalar-or-vector#comment_1693702 for what needs to be done.