Why are the quantities equal to 0?

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In summary: Nerd)I may be wrong about a plus or minus sign, for which you should check your course material. (Worried)But I think the bottom row means that we want to maximize $z$ under the constraint that:$$z - x_2 + 5x_3 = 30 \quad \Rightarrow \quad z = 30 + x_2 - 5x_3$$So if I'm right about the signs, we want to maximize $30 + x_2 - 5x_3$.
  • #1
evinda
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Hello! (Wave)

I am looking at the general form of the Simplex algorithm with the use of tableaux.

$\overline{x_0}$ is a basic non degenarate feasible solution and thus the columns $P_1, \dots, P_m$ are linearly independent.

The first step is to create a $(m+1) \times (n+4)$ matrix as follows:

  • At the first column we write the basic columns: $P-1, \dots, P_m$.
  • At the second column we write the values of the corresponding coefficients of the objective funtion.
  • At the third column we write the initial basic feasible non degenerate solution $\overline{x_0}$.
  • At the next $n$ columns we write the elements of the columns of the matrix $A$.
  • The last column remains empty for now.
  • At the last row we write the value $z_0$ of the objective function that corresponds to the solution $\overline{x_0}$ and also the values of the differences $z_k-c_k, k=1, \dots, n$

Remark

The value of $z_k$ is the dot product of the second and the $(3+k)$-th column.Why does it hold that $z_1-c_1=0, \dots, z_m-c_m=0$ ?

Isn't it $z_1-c_1=c_1 \cdot 1 + c_2 \cdot 0+ \dots + c_m \cdot z_m=c_1$? Or am I wrong? (Thinking)
 
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  • #2
Also, suppose that we are given the following linear programming problem:

$$\max (5x_1-4x_2) \\ x_1-x_2+x_3=6 \\ 3x_1-2x_2+x_4=24 \\ -2x_1+3x_2+x_5=9 \\ x_1 \geq 0, i=1, \dots, 5$$

The first tableau is this:

$$\begin{matrix}
B & c_B & b & P_1 & P_2 & P_3 & P_4 & P_5 & \theta \\
P_3 & 0 & 6 & 1 & -1 & 1 & 0 & 0 & \\
P_4 & 0 & 24 & 3 & -2 & 0 & 1 & 0 & \\
P_5 & 0 & 9 & -2 & 3 & 0 & 0 & 1 & \\
& z & 0 & -5 & 4 & 0& 0 & 0 &
\end{matrix}$$

How did we deduce that $z_1-c_1=-5$ ?
 
  • #3
Hey evinda! (Smile)

What are $c_k$ and $z_k$? (Wondering)

The objective function is $z=5x_1-4x_2 \quad\Rightarrow\quad z -5x_1 + 4x_2 = 0$.
The bottom row consists of those coefficients of $x_k$. (Nerd)
 
  • #4
I like Serena said:
The objective function is $z=5x_1-4x_2 \quad\Rightarrow\quad z -5x_1 + 4x_2 = 0$.
The bottom row consists of those coefficients of $x_k$. (Nerd)

Ah I see... (Nod)

What represents the third column of the bottom row? (Thinking)
 
  • #5
evinda said:
Ah I see... (Nod)

What represents the third column of the bottom row? (Thinking)

Erm... the third column of the bottom row... that seems to be $-5$.
That's the coefficient of $x_1$ in the objective function, multiplied by $-1$. (Thinking)
 
  • #6
I like Serena said:
Erm... the third column of the bottom row... (Thinking)

I meant the column of b...
Do we write $0$ at the last row since there is no 4th component of $b$ or is something else meant?
 
  • #7
evinda said:
I meant the column of b...
Do we write $0$ at the last row since there is no 4th component of $b$ or is something else meant?

Indeed, there is no constant in the function we want to maximize, so the corresponding column $b$ has a $0$ in its position. (Nod)
 
  • #8
I like Serena said:
Indeed, there is no constant in the function we want to maximize, so the corresponding column $b$ has a $0$ in its position. (Nod)

At the second tableaux, at this position there is the number $30$...
So doesn't this mean anything? (Thinking)
 
  • #9
evinda said:
At the second tableaux, at this position there is the number $30$...
So doesn't this mean anything? (Thinking)

I don't see a second tableau. :confused:

Either way, if there is a value of $30$ there, it means we have a constant in the function we want to maximize or minimize. (Nerd)
 
  • #10
I like Serena said:
I don't see a second tableau. :confused:

This is the second tableau:

$\begin{matrix}
B & c_B & b & P_1 & P_2 & P_3 & P_4 & P_5 & \theta\\
P_1 & 5 & 6 & 1 & -1 & 1 & 0 & 0 & - \\
P_4 & 0 & 6 & 0 & 1 & -3 & 1 & 0 & \frac{6}{1}\\
P_5 & 0 & 21 & 0 & 1 & 2 & 0 & 1 & \frac{21}{1} \\
& z & 30 & 0 & -1 & 5 & 0 & 0 &
\end{matrix}$
I like Serena said:
Either way, if there is a value of $30$ there, it means we have a constant in the function we want to maximize or minimize. (Nerd)
Could you explain it further to me? (Thinking)
 
  • #11
evinda said:
This is the second tableau:

$\begin{matrix}
B & c_B & b & P_1 & P_2 & P_3 & P_4 & P_5 & \theta\\
P_1 & 5 & 6 & 1 & -1 & 1 & 0 & 0 & - \\
P_4 & 0 & 6 & 0 & 1 & -3 & 1 & 0 & \frac{6}{1}\\
P_5 & 0 & 21 & 0 & 1 & 2 & 0 & 1 & \frac{21}{1} \\
& z & 30 & 0 & -1 & 5 & 0 & 0 &
\end{matrix}$

Could you explain it further to me? (Thinking)

I may be wrong about a plus or minus sign, for which you should check your course material. (Worried)
But I think the bottom row means that we want to maximize $z$ under the constraint that:
$$z - x_2 + 5x_3 = 30 \quad \Rightarrow \quad z = 30 + x_2 - 5x_3$$
So if I'm right about the signs, we want to maximize $30 + x_2 - 5x_3$.
 

FAQ: Why are the quantities equal to 0?

Why do some quantities have a value of 0?

Quantities can have a value of 0 for a variety of reasons. One possible explanation is that the quantity is not present at all. For example, if we are measuring the number of apples in a basket and there are no apples in the basket, the quantity would be 0. Another reason could be that the quantity has been cancelled out by an equal and opposite quantity, resulting in a net value of 0.

Why is 0 considered a neutral or balancing number?

0 is considered a neutral or balancing number because it represents a balance between positive and negative quantities. For example, if we have 5 apples and we take away 5 apples, the resulting quantity would be 0. It can also be thought of as a midpoint between positive and negative numbers on a number line.

How can 0 be used in mathematical calculations?

0 can be used in mathematical calculations in a variety of ways. It can act as an additive identity, meaning that when 0 is added to any number, the result is that same number. It can also be used as a multiplication identity, meaning that when 0 is multiplied by any number, the result is 0. Additionally, 0 can be used in division as a placeholder for a number that is too small to be represented.

Why is it important to understand the concept of 0 in science?

The concept of 0 is crucial in science because it allows us to accurately measure and compare quantities. In many scientific experiments and calculations, we need to account for the presence or absence of a certain quantity. 0 allows us to represent and understand these relationships. Additionally, 0 is used in many scientific theories and equations, such as the laws of thermodynamics and the concept of absolute zero in temperature.

Can 0 ever have a negative value?

No, 0 can never have a negative value. By definition, 0 represents the absence of a quantity or the midpoint between positive and negative values. It cannot have a negative value because it would then no longer represent this concept. Additionally, 0 is considered a non-negative number, meaning it is greater than or equal to 0, but not less than 0.

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