4.3 Array Broadcasting

The following operations create arrays by repeating elements to fill an array of a specified size. These operations work for all input types T, including reals, integers, vectors, row vectors, matrices, or arrays.

T[] rep_array(T x, int n)
Return the n array with every entry assigned to x.

T[,] rep_array(T x, int m, int n)
Return the m by n array with every entry assigned to x.

T[,,] rep_array(T x, int k, int m, int n)
Return the k by m by n array with every entry assigned to x.

For example, rep_array(1.0,5) produces a real array (type real[]) of size 5 with all values set to 1.0. On the other hand, rep_array(1,5) produces an integer array (type int[]) of size 5 with all values set to 1. This distinction is important because it is not possible to assign an integer array to a real array. For example, the following example contrasts legal with illegal array creation and assignment

 real y[5];
 int x[5];
 
 x = rep_array(1,5);     // ok
 y = rep_array(1.0,5);   // ok
 
 x = rep_array(1.0,5);   // illegal
 y = rep_array(1,5);     // illegal
 
 x = y;                  // illegal
 y = x;                  // illegal

If the value being repeated v is a vector (i.e., T is vector), then rep_array(v,27) is a size 27 array consisting of 27 copies of the vector v.

 vector[5] v;
 vector[5] a[3];
 
 a = rep_array(v,3);  // fill a with copies of v
 a[2,4] = 9.0;        // v[4], a[1,4], a[2,4] unchanged

If the type T of x is itself an array type, then the result will be an array with one, two, or three added dimensions, depending on which of the rep_array functions is called. For instance, consider the following legal code snippet.

 real a[5,6];
 real b[3,4,5,6];
 
 b = rep_array(a,3,4); //  make (3 x 4) copies of a
 b[1,1,1,1] = 27.9;    //  a[1,1] unchanged

After the assignment to b, the value for b[j,k,m,n] is equal to a[m,n] where it is defined, for j in 1:3, k in 1:4, m in 1:5, and n in 1:6.