Problem Statement

Build an   identity matrix   of a size known at run-time.

An identity matrix is a square matrix of size n × n, where the diagonal elements are all 1s (ones), and all the other elements are all 0s (zeroes).

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{\displaystyle I_{n}={\begin{bmatrix}1&0&0&\cdots &0\0&1&0&\cdots &0\0&0&1&\cdots &0\\vdots &\vdots &\vdots &\ddots &\vdots \0&0&0&\cdots &1\\end{bmatrix}}}

Let's start with the solution:

10 INPUT "Matrix size: ";size
20 GO SUB 200: REM Identity matrix
30 FOR r=1 TO size
40 FOR c=1 TO size
50 LET s$=CHR$ 13
60 IF c
70 PRINT i(r,c);s$;
80 NEXT c
90 NEXT r
100 STOP 
200 REM Identity matrix size
220 DIM i(size,size)
230 FOR i=1 TO size
240 LET i(i,i)=1
250 NEXT i
260 RETURN