# Linear Algebra in R, create and invert matrices

This is a simple test case of creating a random 2×2 matrix, performing its inversion, and multiplying them. We will also use MS Excel to check our computations
Create a 2×2 matrix

`> mNP <- matrix(rnorm(4),nrow=2,ncol=2)`

This command used the matrix() function . This first argument, the datasets, uses rnorm() function to generate 4 random variates, and the next two arguments explain that those are to be ordered in a matrix of 2 rows by 2 columns. Now let’s display the matrix

```> mNP [,1] [,2] [1,] 0.5644179 -0.4694577 [2,] 0.7707571 0.1500823```

Next, we use solve() function to invert the matrix, and display the output
``` > mNP_inv <- solve(mNP) > mNP_inv [,1] [,2] [1,] 0.3360953 1.051306 [2,] -1.7260381 1.263961```

Finally, we use the %*% operator to to the algebraic multiplication of the matrices and check if we arrive to I

```> mNP %*% mNP_inv [,1] [,2] [1,] 1 0 [2,] 0 1 > ```

If you would want to do the last operation in Excel, as a check, then let’s suppose that the first matrix sits in fields A1,B1,A2,B2 and the second one sits in fields D1,E1,D2,E2. Their multiplication product would be:
Top left, top right
`=A1*D1+B1*D2 =A1*E1+B1*E2`
Bottom left, bottom right
`=A2*D1+B2*D2 =A2*E1+B2*E2`

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