# Julia 101

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Lesson 3.1: Manipulating Matrices

In Julia, we can define a matrix by typing in a list of numbers enclosed in square brackets.

`A = [0 1 2 3 4 5 6 7 8 9]`

Above statement returns a `1 by 10 Matrix.` A semicolon is used to add a new row in a matrix. The statement

`A = [0 1 2 3 4; 5 6 7 8 9]`

returns a `2 by 5 Matrix.` Matrix can also be define by writing each row on a seperate line. The statement

`A = [0 1 2 3 4;      5 6 7 8 9]orA = [0 1 2 3 4      5 6 7 8 9]`

still returns a `2 by 5 Matrix.`

Julia also allows us to define a matrix in terms of another matrix that has already been defined. For example, statements

`A = [0 1 2 3]B = [A 4 5 6]`

return `B = 0 1 2 3 4 5 6`

We can change or add additional elements to a matrix, by using an index number to specify a particular element. Like MATLAB, in Julia, indexing starts at 1, not 0, therefore command `B[1]`returns `0` and command`B[7]`returns `6.`

The command`B[1] = 10` changes the first value in matrix `B` from `0` to `10.` Similarly, the command`B[4] = 11` changes the fourth value in matrix `B` from `3` to `11.` After these commands, `B` is of the form:

`B = 10 1 2 11 4 5 6`

That’s all for now. In the next lesson, we will discuss how the colon`:` operator is used to define and modify matrices.