[R] add regression equation to panel.lm

[Maria Dulce Subida]

Dear all,

I created a scatterplot matrix with the scatterplot and linear 
regression line in the upper panel, the density histogram in the 
diagonal panel and the values of the Pearson coefficient, probability 
and number of observations used, in the lower panel. Please see the 
script above.
Now I would like to add the regression equation to the upper panel. I 
thought it would be something simple, but I was not able to figure it 
out. Any ideas, please?

Thanks a lot!

Dulce

________________

library(car)
library(psych)

panel.cor <- function(x, y, method="pearson", digits=2,...) {

     points(x,y,type="n");
     usr <- par("usr"); on.exit(par(usr))
     par(usr = c(0, 1, 0, 1));
     correl <- cor.test(x,y, method=method, use="complete.obs");
     sum.row <- rowSums(cbind(x,y));
     conta.n <- length(sum.row[!is.na(sum.row)]);
     n=conta.n;
     r=correl$estimate;
     pval=correl$p.value;
     color="black";
     fontface=1;
     if (pval<0.05) fontface=2;
     txt <- format(r,digits=2)
     pval <- format(pval,digits=2)
     txt <- paste("r= ", txt, "\np=",pval, "\nn=", n, sep="")
     text(0.5, 0.5, txt,col=color, font=fontface)
}

panel.diag<-function(x, ...)
{
     usr <- par("usr"); on.exit(par(usr))
    par(usr = c(usr[1:2], 0, 1.5) )
     h <- hist(x, plot = FALSE)
     breaks <- h$breaks; nB <- length(breaks)
   y <- h$counts; y <- y/max(y)
     rect(breaks[-nB], 0, breaks[-1], y, col="grey", ...)
    d <- density(x,na.rm=TRUE,bw="nrd",adjust=1.2)
     d$y <- d$y/max(d$y)
    lines(d)
}

pairs (~ x + y + z + q, data=my_data, main = "my_data", na.action = 
"na.pass",
diag.panel=panel.diag, upper.panel=panel.lm, col.lm="grey", 
lower.panel=panel.cor,
pch=20, cex=0.5, cex.labels=1, font.labels=2, lwd=0.5)