# plotEqn

##### Plot Linear Equations

Shows what matrices \(A, b\) look like as the system of linear equations, \(A x = b\) with two unknowns, x1, x2, by plotting a line for each equation.

##### Usage

```
plotEqn(A, b, vars, xlim = c(-4, 4), ylim, col = 1:nrow(A), lwd = 2,
lty = 1, axes = TRUE, labels = TRUE, solution = TRUE)
```

##### Arguments

- A
either the matrix of coefficients of a system of linear equations, or the matrix

`cbind(A,b)`

. The`A`

matrix must have two columns.- b
if supplied, the vector of constants on the right hand side of the equations, of length matching the number of rows of

`A`

.- vars
a numeric or character vector of names of the variables. If supplied, the length must be equal to the number of unknowns in the equations. The default is

`paste0("x", 1:ncol(A)`

.- xlim
horizontal axis limits for the first variable

- ylim
vertical axis limits for the second variable; if missing,

`ylim`

is calculated from the range of the set of equations over the`xlim`

.- col
scalar or vector of colors for the lines, recycled as necessary

- lwd
scalar or vector of line widths for the lines, recycled as necessary

- lty
scalar or vector of line types for the lines, recycled as necessary

- axes
logical; draw horizontal and vertical axes through (0,0)?

- labels
logical, or a vector of character labels for the equations; if

`TRUE`

, each equation is labeled using the character string resulting from`showEqn`

- solution
logical; should the solution points for pairs of equations be marked?

##### Value

nothing; used for the side effect of making a plot

##### References

Fox, J. and Friendly, M. (2016). "Visualizing Simultaneous Linear Equations, Geometric Vectors, and
Least-Squares Regression with the matlib Package for R". *useR Conference*, Stanford, CA, June 27 - June 30, 2016.

##### See Also

##### Examples

```
# NOT RUN {
# consistent equations
A<- matrix(c(1,2,3, -1, 2, 1),3,2)
b <- c(2,1,3)
showEqn(A, b)
plotEqn(A,b)
# inconsistent equations
b <- c(2,1,6)
showEqn(A, b)
plotEqn(A,b)
# }
```

*Documentation reproduced from package matlib, version 0.9.2, License: GPL (>= 2)*