Julia 101

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]
or
A = [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 commandB[7]returns 6.

The commandB[1] = 10 changes the first value in matrix B from 0 to 10. Similarly, the commandB[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.