im = idealOfImageOfMap(p)
im = idealOfImageOfMap(phi)
Given a rational map $f : X \to Y \subset P^N$, idealOfImageOfMap returns the defining ideal of the image of $f$ in $P^N$. The rings provided implicitly in the inputs should be polynomial rings or quotients of polynomial rings. In particular, idealOfImageOfMap function returns an ideal defining a subset of the ambient projective space of the image. In the following example we consider the image of $P^1$ inside $P^1 \times P^1$.
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This function frequently just calls ker from Macaulay2. However, if the target of the ring map is a polynomial ring, then it first tries to verify whether the ring map is injective. This is done by computing the rank of an appropriate Jacobian matrix.
The object idealOfImageOfMap is a method function with options.