fix default ncv and errors/warnings

base/linalg/arnoldi.jl

@@ -5,7 +5,7 @@ using .ARPACK
 eigs(A; args...) = eigs(A, I; args...)
 
 function eigs(A, B;
- nev::Integer=6, ncv::Integer=20, which::ASCIIString="LM",
+ nev::Integer=6, ncv::Integer=max(20,2*nev+1), which::ASCIIString="LM",
  tol=0.0, maxiter::Integer=1000, sigma=nothing, v0::Vector=zeros((0,)),
  ritzvec::Bool=true)
 
@@ -14,9 +14,19 @@ function eigs(A, B;
  T = eltype(A)
  iscmplx = T <: Complex
  isgeneral = B !== I
- sym = issym(A)
- (nev = min(nev, sym ? n - 1 : n - 2)) > 0 || throw(ArgumentError("nev must be at least one"))
- ncv = blas_int(min(max(2*nev + 2, ncv), n))
+ sym = issym(A) && !iscmplx
+ nevmax=sym ? n-1 : n-2
+ if nev > nevmax
+ nev = nevmax
+ warn("nev should be at most $nevmax")
+ end
+ nev > 0 || throw(ArgumentError("nev must be at least one"))
+ ncvmin = nev + (sym ? 1 : 2)
+ if ncv < ncvmin
+ warn("ncv should be at least $ncvmin")
+ ncv = ncvmin
+ end
+ ncv = blas_int(min(ncv, n))
  isgeneral && !isposdef(B) && throw(PosDefException(0))
  bmat = isgeneral ? "G" : "I"
  isshift = sigma !== nothing