Elementary random walk — Georg Nees, 1969

Dissertation 1969 · pp. 189 / 194

ALGOL 60

'PROCEDURE' ELIRR.,
'BEGIN'
  JA1.=P+JLI., JE1.=P+JRE.,
  JA2.=Q+JUN., JE2.=Q+JOB.,
  P1.=J1., Q1.=J2.,
  LEER(P1,Q1).,
  'FOR' M.=1 'STEP' 1 'UNTIL' N 'DO'
  'IF' T 'EQUAL' 0 'THEN'
  'BEGIN' LINE(J1,Y)., LINE(X,J2)
  'END'
  'ELSE' LINE(J1,J2).,
  'IF' T 'EQUAL' 0 'THEN'
  'BEGIN' LINE(P1,Y)., LINE(X,Q1)
  'END'
  'ELSE' LINE(P1,Q1)
'END' ELIRR.,

JI1.=JS1., JI2.=JS2.,
N.=20.,
JLI.=0., JRE.=20.,
JUN.=0., JOB.=20.,
T.=0.,
SERIE(20.0,20.0,8,6,ELIRR).,

This page · drawing kernel

JavaScript

JA1 = P + JLI; JE1 = P + JRE;
JA2 = Q + JUN; JE2 = Q + JOB;
const P1 = J1(), Q1 = J2();
LEER(P1, Q1);
for (let M = 1; M <= N; M++) {
  if (T === 0) {
    LINE(J1(), Y);  // horizontal
    LINE(X, J2());  // vertical
  } else LINE(J1(), J2());
}
if (T === 0) { LINE(P1, Y); LINE(X, Q1); }
else LINE(P1, Q1);
// Fig. 22: T=0, N=20, 8×6 cells of 20.

Approximate rendering. Section 3.2.2: ELIRR draws a closed random walk inside the frame rectangle whose bounds are those of J1 and J2 (P+JLI…P+JRE, Q+JUN…Q+JOB). With T = 0 (figure 22) the edges are axis-parallel: new abscissa first, then new ordinate; the close returns to the start. N = 20 gives K = 2·(N+1) corners. JS1 and JS2 are the usual values from p. 122, not those of the printed plate. The generators keep running — figure 23 follows without reseeding. The sheet stands portrait, as in the scan.