# In the simplex algorithm, when might some a variable leave a basis?

 -1 In the simplex algorithm in linear programming, what are conditions for a variable to leave a basis (not necessarily basis for the/an optimal solution)? I'm supposed to list as many sufficient and necessary conditions as possible for some basic variable $$x_q$$ which could be slack, artificial or non-slack and non-artificial. Let $$x_q$$ be the s-th basic variable. Suppose the s-th row of some current simplex tableau has 1 in the column of $$x_q$$ and 0's everywhere else. Under what circumstances, if any, might $$x_q$$ leave the basis? Can any of the values in the s-th row of the tableau ever change? Well since it's a basic variable, I'm guessing the $x_q$ column already has 0's everywhere except in the s-th row. Now, the $x_q$ row has 0's everywhere in the column of $x_q$ like: This is in the context of the Big M Method and artificial variables. I'm not quite sure what the relationship is exactly, though. What I tried: $$x_q$$ leaves if there is some non-basic variable $$x_r$$ that enters because $$z_r - c_r < 0$$ $$z_r - c_r = \min_j (z_j - c_j)$$ $$\frac{b_q'}{a_{qr}'} = \min_i \{\frac{b_i'}{a_{ir}'} | a_{ir}' > 0 \}$$ Is that right? Any other sufficient or necessary conditions? What is the relevance of the 0's in the row? Also, how do I approach the last question? I have no clue. asked 07 May '16, 07:21 BCLC 8●3●11 accept rate: 0%
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