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A useful way to test new ideas in matrix algebra, or to make conjectures, is to make calculations with matrices selected at random. Checking a property for a few matrices does not prove that the property holds in general, but it makes the property more believable. Also, if the property is actually false, you may discover this when you make a few calculations.

38. Use at least three pairs of random \(4 \times 4\) matrices Aand Bto test the equalities \({\left( {A + B} \right)^T} = {A^T} + {B^T}\) and \({\left( {AB} \right)^T} = {A^T}{B^T}\). (See Exercise 37.) Report your conclusions. (Note:Most matrix programs use \(A'\) for \({A^{\bf{T}}}\).

Short Answer

Expert verified

It is verified that\({\left( {A + B} \right)^T} = {A^T} + {B^T}\).

The equality \({\left( {AB} \right)^T} = {A^T}{B^T}\) is incorrect.

Step by step solution

01

MATLAB commands for matrix

To create a random matrix of order \(m \times m\) with random entries, the command \(rand\left( {m,m} \right)\) is used, and the entries are distributed between 0 and 1.

02

Verify the identity by using MATLAB

Test the equality of\({\left( {A + B} \right)^T} = {A^T} + {B^T}\).

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.4126e - 01}&{2.8747e - 03}&{5.9284e - 01}&{3.6762e - 01}\\{3.3928e - 01}&{9.2375e - 01}&{5.1778e - 01}&{2.7072e - 01}\\{1.8617e - 01}&{1.3218e - 01}&{5.4036e - 01}&{2.6490e - 01}\\{1.2837e - 01}&{4.2152e - 01}&{2.1465e - 01}&{4.7236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.481133}&{0.344567}&{0.050269}&{0.879742}\\{0.633319}&{0.630218}&{0.605862}&{0.784503}\\{0.927509}&{0.316194}&{0.850075}&{0.044092}\\{0.102503}&{0.850543}&{0.943759}&{0.455563}\end{aligned}} \right)\)

Now, run the command\({\left( {A + B} \right)^\prime }\).

\({\left( {A + B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{1.0224}&{0.9726}&{1.1137}&{0.2309}\\{0.3474}&{1.5540}&{0.4484}&{1.2721}\\{0.6431}&{1.1236}&{1.3904}&{1.1584}\\{1.2474}&{1.0552}&{0.3090}&{1.9279}\end{aligned}} \right)\)

Run the command \(A' + B'\).

\(A' + B' = \left( {\begin{aligned}{*{20}{c}}{1.0224}&{0.9726}&{1.1137}&{0.2309}\\{0.3474}&{1.5540}&{0.4484}&{1.2721}\\{0.6431}&{0.1236}&{1.3904}&{1.1584}\\{1.2474}&{1.0552}&{0.3090}&{0.9279}\end{aligned}} \right)\)

It is observed that\({\left( {A + B} \right)^\prime } = A' + B'\).

Hence, \({\left( {A + B} \right)^T} = {A^T} + {B^T}\) is verified.

03

Verify the identity by using MATLAB

Test the equality of\({\left( {A + B} \right)^T} = {A^T} + {B^T}\).

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.3126e - 01}&{2.7747e - 03}&{5.9284e - 01}&{3.5762e - 01}\\{3.2928e - 01}&{9.1375e - 01}&{5.0778e - 01}&{2.6072e - 01}\\{1.7617e - 01}&{1.2218e - 01}&{5.3036e - 01}&{2.5490e - 01}\\{1.1837e - 01}&{4.1152e - 01}&{2.0465e - 01}&{4.6236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.381133}&{0.244567}&{0.040269}&{0.779742}\\{0.533319}&{0.530218}&{0.505862}&{0.684503}\\{0.827509}&{0.216194}&{0.750075}&{0.034092}\\{0.002503}&{0.750543}&{0.843759}&{0.355563}\end{aligned}} \right)\)

Now, run the command \({\left( {A + B} \right)^\prime }\).

Now, run the command\({\left( {A + B} \right)^\prime }\).

\({\left( {A + B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{1.0124}&{0.8726}&{1.0137}&{0.1309}\\{0.2474}&{1.4540}&{0.3484}&{1.1721}\\{0.5431}&{1.0236}&{1.2904}&{1.0584}\\{1.1474}&{1.0452}&{0.2090}&{1.8279}\end{aligned}} \right)\)

Run the command \(A' + B'\).

\(A' + B' = \left( {\begin{aligned}{*{20}{c}}{1.0124}&{0.8726}&{1.0137}&{0.1309}\\{0.2474}&{1.4540}&{0.3484}&{1.1721}\\{0.5431}&{0.0236}&{1.2904}&{1.0584}\\{1.1474}&{1.0452}&{0.2090}&{0.8279}\end{aligned}} \right)\)

It is observed that\({\left( {A + B} \right)^\prime } = A' + B'\).

Hence, \({\left( {A + B} \right)^T} = {A^T} + {B^T}\) is verified.

04

Verify the identity by using MATLAB

Test the equality of\({\left( {A + B} \right)^T} = {A^T} + {B^T}\).

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.2126e - 01}&{2.6747e - 03}&{5.9284e - 01}&{3.4762e - 01}\\{3.1928e - 01}&{9.0375e - 01}&{5.0678e - 01}&{2.5072e - 01}\\{1.6617e - 01}&{1.1218e - 01}&{5.2036e - 01}&{2.4490e - 01}\\{1.0837e - 01}&{4.0152e - 01}&{2.0365e - 01}&{4.5236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.281133}&{0.144567}&{0.030269}&{0.679742}\\{0.433319}&{0.430218}&{0.405862}&{0.584503}\\{0.727509}&{0.116194}&{0.650075}&{0.024092}\\{0.001503}&{0.650543}&{0.743759}&{0.255563}\end{aligned}} \right)\)

Now, run the command\({\left( {A + B} \right)^\prime }\).

\({\left( {A + B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{1.0024}&{0.7726}&{1.0037}&{0.0309}\\{0.1474}&{1.3540}&{0.2484}&{1.0721}\\{0.4431}&{1.0136}&{1.1904}&{1.0484}\\{1.0474}&{1.0352}&{0.1090}&{1.7279}\end{aligned}} \right)\)

Run the command \(A' + B'\).

\(A' + B' = \left( {\begin{aligned}{*{20}{c}}{1.0024}&{0.7726}&{1.0037}&{0.0309}\\{0.1474}&{1.3540}&{0.2484}&{1.0721}\\{0.4431}&{0.0136}&{1.1904}&{1.0484}\\{1.0474}&{1.0352}&{0.1090}&{0.7279}\end{aligned}} \right)\)

It is observed that\({\left( {A + B} \right)^\prime } = A' + B'\).

Hence, \({\left( {A + B} \right)^T} = {A^T} + {B^T}\) is verified.

05

Verify the identity by using MATLAB

Test the equality of\({\left( {AB} \right)^T} = {A^T}{B^T}\).

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.2126e - 01}&{2.6747e - 03}&{5.9284e - 01}&{3.4762e - 01}\\{3.1928e - 01}&{9.0375e - 01}&{5.0678e - 01}&{2.5072e - 01}\\{1.6617e - 01}&{1.1218e - 01}&{5.2036e - 01}&{2.4490e - 01}\\{1.0837e - 01}&{4.0152e - 01}&{2.0365e - 01}&{4.5236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.281133}&{0.144567}&{0.030269}&{0.679742}\\{0.433319}&{0.430218}&{0.405862}&{0.584503}\\{0.727509}&{0.116194}&{0.650075}&{0.024092}\\{0.001503}&{0.650543}&{0.743759}&{0.255563}\end{aligned}} \right)\)

Now, run the command\({\left( {A*B} \right)^\prime }\).

\({\left( {A*B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{0.8498}&{1.2563}&{0.7016}&{0.5762}\\{0.6884}&{1.0930}&{0.5436}&{0.7795}\\{0.8799}&{1.2724}&{0.7988}&{0.8901}\\{0.6720}&{1.1693}&{0.4120}&{0.6683}\end{aligned}} \right)\)

Run the command \(A'*B'\).

\(A'*B' = \left( {\begin{aligned}{*{20}{c}}{1.0024}&{0.7726}&{1.0037}&{0.0309}\\{0.1474}&{1.3540}&{0.2484}&{1.0721}\\{0.4431}&{0.0136}&{1.1904}&{1.0484}\\{1.0474}&{1.0352}&{0.1090}&{0.7279}\end{aligned}} \right)\)

It is observed that\({\left( {A*B} \right)^\prime } \ne A'*B'\).

Hence, the equality \({\left( {AB} \right)^T} = {A^T}{B^T}\) is incorrect.

06

Verify the identity by using MATLAB

Test the equality of\({\left( {AB} \right)^T} = {A^T}{B^T}\).

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.3126e - 01}&{2.7747e - 03}&{5.9284e - 01}&{3.5762e - 01}\\{3.2928e - 01}&{9.1375e - 01}&{5.0778e - 01}&{2.6072e - 01}\\{1.7617e - 01}&{1.2218e - 01}&{5.3036e - 01}&{2.5490e - 01}\\{1.1837e - 01}&{4.1152e - 01}&{2.0465e - 01}&{4.6236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.381133}&{0.244567}&{0.040269}&{0.779742}\\{0.533319}&{0.530218}&{0.505862}&{0.684503}\\{0.827509}&{0.216194}&{0.750075}&{0.034092}\\{0.002503}&{0.750543}&{0.843759}&{0.355563}\end{aligned}} \right)\)

Now, run the command\({\left( {A*B} \right)^\prime }\).

\({\left( {A*B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{0.7498}&{1.1563}&{0.6016}&{0.4762}\\{0.5884}&{1.0830}&{0.4436}&{0.6795}\\{0.7799}&{1.1724}&{0.6988}&{0.7901}\\{0.5720}&{1.0693}&{0.3120}&{0.5683}\end{aligned}} \right)\)

Run the command \(A'*B'\).

\(A'*B' = \left( {\begin{aligned}{*{20}{c}}{1.0014}&{0.6726}&{1.0027}&{0.0209}\\{0.0474}&{1.2540}&{0.1484}&{1.0621}\\{0.3431}&{0.0036}&{1.0904}&{1.0384}\\{1.0374}&{1.0252}&{0.0090}&{0.6279}\end{aligned}} \right)\)

It is observed that\({\left( {A*B} \right)^\prime } \ne A'*B'\).

Hence, the equality \({\left( {AB} \right)^T} = {A^T}{B^T}\) is incorrect.

07

Verify the identity by using MATLAB

Create a random matrix\(A\)by using MATLAB command as shown below:

\( > > A = rand\left( {4,4} \right)\)

The output of matrix A as shown below:

\({\rm{A}} = \left( {\begin{aligned}{*{20}{c}}{5.2126e - 01}&{2.6747e - 03}&{5.9284e - 01}&{3.4762e - 01}\\{3.1928e - 01}&{9.0375e - 01}&{5.0678e - 01}&{2.5072e - 01}\\{1.6617e - 01}&{1.1218e - 01}&{5.2036e - 01}&{2.4490e - 01}\\{1.0837e - 01}&{4.0152e - 01}&{2.0365e - 01}&{4.5236e - 01}\end{aligned}} \right)\)

Create a random matrix B by using MATLAB command as shown below:

\( > > B = rand\left( {4,4} \right)\)

The output of matrix B as shown below:

\({\rm{B}} = \left( {\begin{aligned}{*{20}{c}}{0.281133}&{0.144567}&{0.030269}&{0.679742}\\{0.433319}&{0.430218}&{0.405862}&{0.584503}\\{0.727509}&{0.116194}&{0.650075}&{0.024092}\\{0.001503}&{0.650543}&{0.743759}&{0.255563}\end{aligned}} \right)\)

Now, run the command\({\left( {A*B} \right)^\prime }\).

\({\left( {A*B} \right)^\prime } = \left( {\begin{aligned}{*{20}{c}}{0.6498}&{1.0563}&{0.5016}&{0.3762}\\{0.4884}&{1.0730}&{0.3436}&{0.5795}\\{0.6799}&{1.0724}&{0.5988}&{0.6901}\\{0.4720}&{1.0593}&{0.2120}&{0.4683}\end{aligned}} \right)\)

Run the command \(A'*B'\).

\(A'*B' = \left( {\begin{aligned}{*{20}{c}}{1.0004}&{0.5726}&{1.0017}&{0.0109}\\{0.0374}&{1.1540}&{0.0484}&{1.0521}\\{0.2431}&{0.0026}&{1.0804}&{1.0284}\\{1.0274}&{1.0152}&{0.0080}&{0.5279}\end{aligned}} \right)\)

It is observed that\({\left( {A*B} \right)^\prime } \ne A'*B'\).

Hence, the equality\({\left( {AB} \right)^T} = {A^T}{B^T}\)is incorrect.

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