Define a matrix : matrix

### 2.42.25 Define a matrix : `matrix`

`matrix` takes three arguments :

- two integers n and p.
- a function of two variables `j` and `k` which should return the value of aj,k, the element of row index `j` and column index `k` of the matrix to be build.

`matrix` returns the matrix A=(aj,k) (j=1..n and k=1..p) of dimension n × p.
Input :

`matrix(4,3,(j,k)->j+k)`

or first define the h function:

`h(j,k):=j+k`

then, input:

`matrix(4,3,h)`

Output :

`[[2,3,4],[3,4,5],[4,5,6],[5,6,7]]`

Note the argument order and the fact that the indices are counted starting from 1. If the last argument is not provided, it defaults to 0.