By joining a table onto itself, you can look at expressions of values
from the same column but different records. For example, suppose you
want to plot the derivative of column
NE where you have NE as a function of
RADIUS and TIME, and TIME is evenly spaced with an
increment of 0.01 seconds. You would join this table with itself, such
that the rows are offset. To do this, first go back to the top menu
(\0) and select two copies of the table: PT GP8840
GP8840;. Then select the JOIN option and define the join as
(A.TIME-0.01=B.TIME)AND(A.RADIUS=B.RADIUS). Now for the y
axis, you can specify (A.NE-B.NE)/(A.TIME-B.TIME) as in
Figure 7.
\* Options are:
1) Y < (A.NE-B.NE)/(A.TIME-B.TIME) >
2) X < TIME >
3) Constraints < RADIUS=70 (TIME>2.8)AND(TIME<3.4) >
4) Symbols < >
5) Graph ranges <Y:0.00E+00,0.00E+00,LIN><X:0.00E+00,0.00E+00,LIN>
6) G+ Graph Plus <Auto-scale_Y:min=T,max=T><Auto-scale_X:min=T,max=T>
7) Key for dynamic cursor option <A.NE>
8) Join <(A.TIME-0.01=B.TIME)AND(A.RADIUS=B.RADIUS)>
...
A join of (A.TIME-0.02=B.TIME)AND(A.RADIUS=B.RADIUS), i.e., over
two records, would result in a smoother derivative. By defining
(A.NE-B.NE)/(A.TIME-B.TIME) as DNEDT in an expression table,
you can succintly use the derivative in other expressions.
Figure 7: Plot a derivative by joining a table with itself