I am fitting 3 parameter model to my response matrix and want to generate
item characterstic curve.
I want to specify file name to save item characterstic curve by passing it
as external parameter to the R batch script. The following is the code I
have written for this.

*R Script:*

library(ltm)
cmd_args = commandArgs();
for (arg in cmd_args) cat("  ", arg, "\n", sep="")
respmat <- read.table("C:\\rphp\\responsedata.txt")
fit3pl <- tpm(respmat)
cat("  ", arg, "\n", sep="")
b <- c("C:\\rphp\\",arg)
png(file=b, bg="transparent")
plot(fit3pl,items=c,lwd=3)
dev.off()
rm(respmat,fit3pl,b)
q()

Could you please help me in doing so? I get an error message when R executes
png().

Thanks and Regards,
Maulik

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