Function fold_highest_var 

pub fn fold_highest_var<A: Allocator, P: PackedField, Data: Deref<Target = [P]>>(
    alloc: &A,
    values: &FieldBuffer<P, Data>,
    scalar: P::Scalar,
) -> FieldVec<P, A>

Fixes the highest variable of a multilinear to a value, writing into memory from an allocator.

g(X_0, ..., X_{n-2}) = f(X_0, ..., X_{n-2}, r)

Each output coefficient interpolates the line through one pair of input coefficients. The input is left untouched.

Use this when the input is borrowed or must be preserved. Otherwise prefer the form that overwrites the input.

Preconditions

• the buffer must have at least one variable