Divide by zero / bullseyes

[Jason Shafer]

Hi Folks,

I'm having problems plotting 1/quantity where the quantity is derived. In
this case, the derived quantity is temperature gradient:

'define grad1 = ((-ty/dy)+(tx/dx))'

I have no problem computing and plotting this. However, when I simply try to
plot 1/grad1 all I get are a handful of bullsyes and not the inverse of the
field! Any suggestions or help? I suspect it might have something to do with
dividing by zero where the field might be zero? Thanks!

Jay