For solve
you need to give your original matrix, but for chol2inv
you use precomputed cholesky decomposition:
set.seed(1)
a<-crossprod(matrix(rnorm(9),3,3))
a_chol<-chol(a)
solve(a)
[,1] [,2] [,3]
[1,] 1.34638151 -0.02957435 0.8010735
[2,] -0.02957435 0.32780020 -0.1786295
[3,] 0.80107345 -0.17862950 1.4533671
chol2inv(a_chol)
[,1] [,2] [,3]
[1,] 1.34638151 -0.02957435 0.8010735
[2,] -0.02957435 0.32780020 -0.1786295
[3,] 0.80107345 -0.17862950 1.4533671