increase_arity: Increase arity of a spray object
In CharlotteJana/pdmppoly: Moment Approximation for Polynomial PDMPs

Description Usage Arguments Details Note Examples

Increase the arity of a spray object by adding new columns (with zeros) to the index matrix of the spray object.

1	increase_arity(S, position)

`S`	spray object that shall have a new arity
`position`	column indexes where to add new variables

The arity of a spray object defines the dimension of the polynomial. For example lone(1, 2) and lone(1, 5) look the same when printed to the console, but differ in their arity (2 or 5). This can be seen by using method print_spray_matrixform. Calculation with spray objects (sum, product etc.) is only possible if the spray objects havte the same arity. This is where function increase_arity comes into play. It can increase the arity of a polynomial/spray object by adding new variables. This means essentially inserting new columns with zeros in the index matrix of the spray object. The argument position defines the columnindex of these additinoal columns.

If S is the NULL polynomial without a given arity (this can arise for example by using method subs), the returned spray object will be the NULL polynomial with its arity given as the maximal entry in vector positions.

library(spray)
lone(1, 5) + lone(1, 2) # throws error
lone(1, 5) + increase_arity(lone(1, 2), 3:5)

print_spray_matrixform(homog(2, 3))
s <- increase_arity(homog(2, 3), 2) # insert variable in the middle
print_spray_matrixform(s)

p <- subs(product(1:4), dims = 2:3, x = c(-1, 2)) # substitute values
increase_arity(p, 2:3) # keep arity as before the substitution

q <- subs(lone(1,1), 1, 0) # NULL polynomial without arity
increase_arity(q, c(2, 5))