One pivot: entering column, ratio test, and row reduction

Intermediate Simplex algorithm, StatQuest
Created by Best · 15.07.2026 at 20:54 UTC

A single move of the algorithm has two decisions and one calculation. First, choose which variable to increase by scanning the top row for the largest negative number. If the cookie column holds $-3$, the most negative entry, you move along the cookie axis.

Second, decide how far to go with the ratio test: for the entering column, divide each constraint row's total by that row's positive entry in the entering column. You choose the smallest ratio, because any larger ratio would land outside the feasible region. If two ratios tie for smallest, take the row with the lower index.

Then comes the calculation, Gaussian elimination on that column. Scale the chosen row so its entry in the entering column becomes $1$, then add multiples of it to the other rows so every other entry in that column becomes $0$. Now you read coordinates straight off the tableau: a column that is a single $1$ with zeros elsewhere means that variable equals its paired total, while a column still mixing several values reads as zero for that variable. The upper-right corner tracks revenue at the current vertex.

University approvals: 0
Related cards
Builds on Building the simplex tableau · Simplex algorithm, StatQuest
Next Iterating to the optimum, and a three-variable run · Simplex algorithm, StatQuest
Video Content
Tasks
Question 1

How do you choose the column to move along (the entering variable)?

Question 2

The ratio test gives $25$, $16.7$, and $10$. Which do you pick, and why?

Question 3

After row reduction, how do you read a variable's value from a column?

Question 4

Where does the current revenue appear in the tableau?

Card Info
  • Topic: Simplex algorithm, StatQuest
  • Difficulty: Intermediate
  • Completed: 0 users
Creator
Best
Best
BestBuddy