14.2.4 Creating a matrix with a formula or function
Use a function or a formula to specify the elements of a
matrix with the makemat
or matrix command.
-
makemat takes three arguments:
-
f, a function of two variables j and
k which returns the value of aj,k, the element at
row index j and column index k of the resulting
matrix.
- n and p, two positive integers.
- makemat(f,n,p) returns the n× p matrix
A=[ajk] with ajk=f(j,k) for j=1…,n and k=1,…,p.
The matrix command can be used similarly, but note that the
arguments are given in a different order and the indices start at 1.
(See Section 14.4.2 for other uses of matrix.)
-
matrix takes two mandatory arguments and one optional
argument:
-
n and p, two integers.
- Optionally, f, a function of two variables j and
k which should return the value of aj,k, the element at
row index j and column index k of the resulting
matrix.
- matrix(n,p) returns the n× p matrix consisting of
all zeros.
- matrix(n,p,f) returns the n× p matrix
A=[ajk] with ajk=f(j,k) for j=1,…,n and k=1,…,p.
Examples
or:
h(j,k):=j+k:;
makemat(h,4,3) |
Note that the indices are counted starting from 0.
or:
h(j,k):=j+k:;
matrix(4,3,h) |