I have variables $X1,...,X10$ and $X1hat,..., X10hat$ in a system of equations. How can I refer to these variables in a summation? I am looking for something like:

Sum[X`i' X`i'hat,{i,10}]
  • $\begingroup$ Instead of x1, use x[1]. Then you can use x[i]. $\endgroup$ – Szabolcs May 7 '17 at 7:37
  • $\begingroup$ Thanks! It solved my problem for variables. But is there also a way to do something similar for an equation to avoid writing it multiple times? For example instead of writing eq1=X[1]^2,...,eq10=X[10]^2, write something like: {eq[i] = X[i]^2, {i, 10}} in a system of equations? $\endgroup$ – Hossein May 7 '17 at 7:51
  • $\begingroup$ Use Table to make a list of equations. $\endgroup$ – Szabolcs May 7 '17 at 8:55

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