Function to add a grid to an existing (barycentric) plot.

```
trigrid(x = seq(0.1, 0.9, by = 0.1), y = NULL, z = NULL,
lty = "dashed", col = "grey", ...)
```

x

Values along which to draw grid lines for first dimension
(or all dimensions if `y`

and `z`

omitted).
For NO grid lines in some dimensions just supply an `NA`

.

y

Grid lines for second dimension.

z

Grid lines for third dimension.

lty

Line type (see `par`

).

col

Line colour (see `par`

).

…

Further graphical parameters passed to `trilines`

.

Grid lines illustrate the set of points for which one of the dimensions is held constant; e.g. horizontal lines contain all points with a certain value y for the second dimension, connecting the two extreme points (0,y,1-y) and (1-y,y,0).

Grids may be designed more flexible than with `triplot`

's `grid`

option.

# NOT RUN { triplot(grid = FALSE) trigrid(c(1/3, 0.5)) # same grid for all 3 dimensions triplot(grid = c(1/3, 0.5)) # (same effect) triplot(grid = FALSE) # different grids for all dimensions: trigrid(x = 1/3, y = 0.5, z = seq(0.2, 0.8, by=0.2)) triplot(grid = FALSE) # grid for third dimension only: trigrid(x = NA, y = NA, z = c(0.1, 0.2, 0.4, 0.8)) # }