Page 381 - Excel for Scientists and Engineers: Numerical Methods

358 EXCEL: NUMERICAL METHODS

=50*RAND()

and
=35*RAND()
and the formula in C17 contains the custom function
=Inside($A$6:$A$14 ,$ B$6:$B$14 ,A1 7, B 1 7)
The formulas were filled down to fill 2000 cells. The formulas to calculate
the area are:
in cell D7: =COUNTA($C$I 7:$C$2016) (total number of points)
in cell E7: {=SUM(($C$17:$C$2016)*1)} (number of points inside polygon)
in cell E9: =E7/D7 (fraction of points inside)
in cell D11: =35*50 (area of the "box")
in cell El 1 : =E9*D11 (area of polygon)

To plot only the points that lie within the polygon, the formula
=IF($C17,A17,"")
in cell D17 and the formula
=I F( $C 1 7, B 1 7 ,"")
in cell El7 would seem to be suitable. These formulas, w.,en filleL down, yield
the spreadsheet shown in Figure 15-19. But null-string values are plotted as
zeros in a chart, so the chart doesn't turn out the way we want. Instead we use
the NA() worksheet function; cells containing #NA! values are not plotted.

=IF($CI 7,A17,NA())