Hi all, I want to draw n plots whose titles are "Main effect of X_i", i= 1, 2, ..., n, respectively. More specifically, I use: par(mfrow = c(n/2, 2)) for ( i in 1:n) { plot(1:J, y[i, 1: J], main = 'Main effect of X_i') } This gives me a series of plots with the common title with a letter i in it, not the consecutive numbers I want. Thanks in advance. Xinxin