A data dependence is loop independent if dependence is between instances in the same iteration
Consider a loop

there is a loop independent dependence from S₁ to S₂ if there is an integer i such that

OR

there is an iteration in which S₁ writes into X and S₂ reads from the same element of X.

A data dependence is loop dependent if dependence is between different iterations.

there is a loop dependent dependence from S₁ to S₂ if there exist integers i₁ and i₂ such that

OR

S₁ writes into X in iteration i₁ and S₂ reads from the same location in a later iteration i₂.

Therefore, to find out data dependence from S₁ to S₂, one has to solve