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Matrix of Relation

Mathematics · FE Reference Handbook section

Mathematics
2 formulas
10 exam-style examples
~49 min
All Mathematics lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Entries in a relation (adjacency) matrix — solve for matrix entries — Matrix of Relation

a relation matrix linking survey stations to control points Given rows (elements of the first set) (n_r) = 9.0000; columns (elements of the second set) (n_c) = 17.0000, determine the matrix entries (E) in entries.

Given

  • rows(elementsofthefirstset)(nr)=9.0000rows (elements of the first set) (n_r) = 9.0000
  • columns(elementsofthesecondset)(nc)=17.0000columns (elements of the second set) (n_c) = 17.0000

Find

matrix entries (E), in entries

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for E:

    E=nrncE = n_r n_c
  3. Step 3 — List the givens: rows (elements of the first set) (n_r) = 9.0000, columns (elements of the second set) (n_c) = 17.0000.

  4. Step 4 — Substitute the given values:

    E=nrncE = n_r n_c
  5. Step 5 — Evaluate:

    E=153.0 entriesE = 153.0\ \text{entries}
  6. Step 6 — Check: returning E = 153.0 entries to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=153.0 entriesE = 153.0\ \text{entries}

Why the other options are there

  • 306.0 — kept a factor of two that cancels in the correct rearrangement.
  • 76.5000 — dropped that same factor in the other direction.
  • 168.3 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 2
Entries in a relation (adjacency) matrix — solve for rows (elements of the first set) — Matrix of Relation (2)

a finite state machine transition table stored as a Boolean matrix Given matrix entries (E) = 232.0 entries; columns (elements of the second set) (n_c) = 9.0000, determine the rows (elements of the first set) (n_r).

Given

  • matrixentries(E)=232.0entriesmatrix entries (E) = 232.0 entries
  • columns(elementsofthesecondset)(nc)=9.0000columns (elements of the second set) (n_c) = 9.0000

Find

rows (elements of the first set) (n_r)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_r is given, so isolate n_r symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_r:

    nr=Encn_{r} = \dfrac{E}{n_c}
  3. Step 3

    Listthegivens:matrixentries(E)=232.0entries,columns(elementsofthesecondset)(nc)=9.0000List the givens: matrix entries (E) = 232.0 entries, columns (elements of the second set) (n_c) = 9.0000
  4. Step 4 — Substitute the given values:

    nr=232.0ncn_{r} = \dfrac{232.0}{n_c}
  5. Step 5 — Evaluate:

    nr=25.7778n_{r} = 25.7778
  6. Step 6 — Check: returning n_r = 25.7778 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nr=25.7778n_{r} = 25.7778

Why the other options are there

  • 51.5556 — kept a factor of two that cancels in the correct rearrangement.
  • 12.8889 — dropped that same factor in the other direction.
  • 28.3556 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 3
Entries in a relation (adjacency) matrix — solve for columns (elements of the second set) — Matrix of Relation (3)

a relation matrix linking pipe nodes to demand nodes Given matrix entries (E) = 353.0 entries; rows (elements of the first set) (n_r) = 18.0000, determine the columns (elements of the second set) (n_c).

Given

  • matrixentries(E)=353.0entriesmatrix entries (E) = 353.0 entries
  • rows(elementsofthefirstset)(nr)=18.0000rows (elements of the first set) (n_r) = 18.0000

Find

columns (elements of the second set) (n_c)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_c is given, so isolate n_c symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_c:

    nc=Enrn_{c} = \dfrac{E}{n_r}
  3. Step 3

    Listthegivens:matrixentries(E)=353.0entries,rows(elementsofthefirstset)(nr)=18.0000List the givens: matrix entries (E) = 353.0 entries, rows (elements of the first set) (n_r) = 18.0000
  4. Step 4 — Substitute the given values:

    nc=353.0nrn_{c} = \dfrac{353.0}{n_r}
  5. Step 5 — Evaluate:

    nc=19.6111n_{c} = 19.6111
  6. Step 6 — Check: returning n_c = 19.6111 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nc=19.6111n_{c} = 19.6111

Why the other options are there

  • 39.2222 — kept a factor of two that cancels in the correct rearrangement.
  • 9.8056 — dropped that same factor in the other direction.
  • 21.5722 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 4
Entries in a relation (adjacency) matrix — solve for matrix entries (case 2) — Matrix of Relation (4)

a relation matrix linking survey stations to control points Given rows (elements of the first set) (n_r) = 19.0000; columns (elements of the second set) (n_c) = 10.0000, determine the matrix entries (E) in entries.

Given

  • rows(elementsofthefirstset)(nr)=19.0000rows (elements of the first set) (n_r) = 19.0000
  • columns(elementsofthesecondset)(nc)=10.0000columns (elements of the second set) (n_c) = 10.0000

Find

matrix entries (E), in entries

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for E:

    E=nrncE = n_r n_c
  3. Step 3 — List the givens: rows (elements of the first set) (n_r) = 19.0000, columns (elements of the second set) (n_c) = 10.0000.

  4. Step 4 — Substitute the given values:

    E=nrncE = n_r n_c
  5. Step 5 — Evaluate:

    E=190.0 entriesE = 190.0\ \text{entries}
  6. Step 6 — Check: returning E = 190.0 entries to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=190.0 entriesE = 190.0\ \text{entries}

Why the other options are there

  • 380.0 — kept a factor of two that cancels in the correct rearrangement.
  • 95.0000 — dropped that same factor in the other direction.
  • 209.0 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 5
Entries in a relation (adjacency) matrix — solve for rows (elements of the first set) (case 2) — Matrix of Relation (5)

a finite state machine transition table stored as a Boolean matrix Given matrix entries (E) = 113.0 entries; columns (elements of the second set) (n_c) = 5.0000, determine the rows (elements of the first set) (n_r).

Given

  • matrixentries(E)=113.0entriesmatrix entries (E) = 113.0 entries
  • columns(elementsofthesecondset)(nc)=5.0000columns (elements of the second set) (n_c) = 5.0000

Find

rows (elements of the first set) (n_r)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_r is given, so isolate n_r symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_r:

    nr=Encn_{r} = \dfrac{E}{n_c}
  3. Step 3

    Listthegivens:matrixentries(E)=113.0entries,columns(elementsofthesecondset)(nc)=5.0000List the givens: matrix entries (E) = 113.0 entries, columns (elements of the second set) (n_c) = 5.0000
  4. Step 4 — Substitute the given values:

    nr=113.0ncn_{r} = \dfrac{113.0}{n_c}
  5. Step 5 — Evaluate:

    nr=22.6000n_{r} = 22.6000
  6. Step 6 — Check: returning n_r = 22.6000 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nr=22.6000n_{r} = 22.6000

Why the other options are there

  • 45.2000 — kept a factor of two that cancels in the correct rearrangement.
  • 11.3000 — dropped that same factor in the other direction.
  • 24.8600 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 6
Entries in a relation (adjacency) matrix — solve for columns (elements of the second set) (case 2) — Matrix of Relation (6)

a relation matrix linking pipe nodes to demand nodes Given matrix entries (E) = 346.0 entries; rows (elements of the first set) (n_r) = 16.0000, determine the columns (elements of the second set) (n_c).

Given

  • matrixentries(E)=346.0entriesmatrix entries (E) = 346.0 entries
  • rows(elementsofthefirstset)(nr)=16.0000rows (elements of the first set) (n_r) = 16.0000

Find

columns (elements of the second set) (n_c)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_c is given, so isolate n_c symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_c:

    nc=Enrn_{c} = \dfrac{E}{n_r}
  3. Step 3

    Listthegivens:matrixentries(E)=346.0entries,rows(elementsofthefirstset)(nr)=16.0000List the givens: matrix entries (E) = 346.0 entries, rows (elements of the first set) (n_r) = 16.0000
  4. Step 4 — Substitute the given values:

    nc=346.0nrn_{c} = \dfrac{346.0}{n_r}
  5. Step 5 — Evaluate:

    nc=21.6250n_{c} = 21.6250
  6. Step 6 — Check: returning n_c = 21.6250 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nc=21.6250n_{c} = 21.6250

Why the other options are there

  • 43.2500 — kept a factor of two that cancels in the correct rearrangement.
  • 10.8125 — dropped that same factor in the other direction.
  • 23.7875 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 7
Entries in a relation (adjacency) matrix — solve for matrix entries (case 3) — Matrix of Relation (7)

a relation matrix linking survey stations to control points Given rows (elements of the first set) (n_r) = 11.0000; columns (elements of the second set) (n_c) = 4.0000, determine the matrix entries (E) in entries.

Given

  • rows(elementsofthefirstset)(nr)=11.0000rows (elements of the first set) (n_r) = 11.0000
  • columns(elementsofthesecondset)(nc)=4.0000columns (elements of the second set) (n_c) = 4.0000

Find

matrix entries (E), in entries

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for E:

    E=nrncE = n_r n_c
  3. Step 3 — List the givens: rows (elements of the first set) (n_r) = 11.0000, columns (elements of the second set) (n_c) = 4.0000.

  4. Step 4 — Substitute the given values:

    E=nrncE = n_r n_c
  5. Step 5 — Evaluate:

    E=44.0000 entriesE = 44.0000\ \text{entries}
  6. Step 6 — Check: returning E = 44.0000 entries to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=44.0000 entriesE = 44.0000\ \text{entries}

Why the other options are there

  • 88.0000 — kept a factor of two that cancels in the correct rearrangement.
  • 22.0000 — dropped that same factor in the other direction.
  • 48.4000 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 8
Entries in a relation (adjacency) matrix — solve for rows (elements of the first set) (case 3) — Matrix of Relation (8)

a finite state machine transition table stored as a Boolean matrix Given matrix entries (E) = 90.0000 entries; columns (elements of the second set) (n_c) = 17.0000, determine the rows (elements of the first set) (n_r).

Given

  • matrixentries(E)=90.0000entriesmatrix entries (E) = 90.0000 entries
  • columns(elementsofthesecondset)(nc)=17.0000columns (elements of the second set) (n_c) = 17.0000

Find

rows (elements of the first set) (n_r)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_r is given, so isolate n_r symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_r:

    nr=Encn_{r} = \dfrac{E}{n_c}
  3. Step 3

    Listthegivens:matrixentries(E)=90.0000entries,columns(elementsofthesecondset)(nc)=17.0000List the givens: matrix entries (E) = 90.0000 entries, columns (elements of the second set) (n_c) = 17.0000
  4. Step 4 — Substitute the given values:

    nr=90.0000ncn_{r} = \dfrac{90.0000}{n_c}
  5. Step 5 — Evaluate:

    nr=5.2941n_{r} = 5.2941
  6. Step 6 — Check: returning n_r = 5.2941 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nr=5.2941n_{r} = 5.2941

Why the other options are there

  • 10.5882 — kept a factor of two that cancels in the correct rearrangement.
  • 2.6471 — dropped that same factor in the other direction.
  • 5.8235 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 9
Entries in a relation (adjacency) matrix — solve for columns (elements of the second set) (case 3) — Matrix of Relation (9)

a relation matrix linking pipe nodes to demand nodes Given matrix entries (E) = 335.0 entries; rows (elements of the first set) (n_r) = 10.0000, determine the columns (elements of the second set) (n_c).

Given

  • matrixentries(E)=335.0entriesmatrix entries (E) = 335.0 entries
  • rows(elementsofthefirstset)(nr)=10.0000rows (elements of the first set) (n_r) = 10.0000

Find

columns (elements of the second set) (n_c)

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except n_c is given, so isolate n_c symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for n_c:

    nc=Enrn_{c} = \dfrac{E}{n_r}
  3. Step 3

    Listthegivens:matrixentries(E)=335.0entries,rows(elementsofthefirstset)(nr)=10.0000List the givens: matrix entries (E) = 335.0 entries, rows (elements of the first set) (n_r) = 10.0000
  4. Step 4 — Substitute the given values:

    nc=335.0nrn_{c} = \dfrac{335.0}{n_r}
  5. Step 5 — Evaluate:

    nc=33.5000n_{c} = 33.5000
  6. Step 6 — Check: returning n_c = 33.5000 to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
nc=33.5000n_{c} = 33.5000

Why the other options are there

  • 67.0000 — kept a factor of two that cancels in the correct rearrangement.
  • 16.7500 — dropped that same factor in the other direction.
  • 36.8500 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

Example 10
Entries in a relation (adjacency) matrix — solve for matrix entries (case 4) — Matrix of Relation (10)

a relation matrix linking survey stations to control points Given rows (elements of the first set) (n_r) = 9.0000; columns (elements of the second set) (n_c) = 4.0000, determine the matrix entries (E) in entries.

Given

  • rows(elementsofthefirstset)(nr)=9.0000rows (elements of the first set) (n_r) = 9.0000
  • columns(elementsofthesecondset)(nc)=4.0000columns (elements of the second set) (n_c) = 4.0000

Find

matrix entries (E), in entries

Start with the thinking

  • The governing relation printed in this handbook section is Entries in a relation (adjacency) matrix.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A relation between two finite sets is stored as a Boolean matrix of relation, so the storage cost is the entry count.

Step-by-step solution

  1. Step 1 — State the governing relation:

    E=nrncE = n_r n_c
  2. Step 2 — Rearrange symbolically for E:

    E=nrncE = n_r n_c
  3. Step 3 — List the givens: rows (elements of the first set) (n_r) = 9.0000, columns (elements of the second set) (n_c) = 4.0000.

  4. Step 4 — Substitute the given values:

    E=nrncE = n_r n_c
  5. Step 5 — Evaluate:

    E=36.0000 entriesE = 36.0000\ \text{entries}
  6. Step 6 — Check: returning E = 36.0000 entries to

    E=nrncE = n_r n_c

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=36.0000 entriesE = 36.0000\ \text{entries}

Why the other options are there

  • 72.0000 — kept a factor of two that cancels in the correct rearrangement.
  • 18.0000 — dropped that same factor in the other direction.
  • 39.6000 — rounded an intermediate value before the final step.

Reference: FE Handbook — Discrete Mathematics (Matrix of Relation)

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