If-then statement

[Helen Chang <helen.chang@cognigencorp.com>]

Hi, All:

I am trying to modify this one standard expression to accomodate the
if-then statements. But I got syntax error after I did that. Below are
the codes

1.Standard expression:

form<-expression((1/v*ka)/(ka-ke)*(exp(-ke*(t-tlag))-exp(-ka*(t-tlag))))


2. The if-then expression:

  model1 <- if (0<=t<=tlag) {
  ((1/v*ka)/(ka-ke)*(exp(-ke*t)-exp(-ka*t)))}

   model2 <- else  {
  ((1/v*ka)/(ka-ke)*(exp(-ke*(t-tlag))-exp(-ka*(t-tlag))))}

  form<-c(expression(model1),expression(model2))

Any suggestion will be greatly appreciated.

Thank you.

Helen