From 4baf521834e33c45aca32bb69fe7290a418a6660 Mon Sep 17 00:00:00 2001
From: Rik Huijzer <t.h.huijzer@rug.nl>
Date: Mon, 20 Dec 2021 11:37:16 +0100
Subject: [PATCH] Point to cov if not positive definite (#746)

---
 src/reliability.jl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/reliability.jl b/src/reliability.jl
index aebb94b29..e9abb58b3 100644
--- a/src/reliability.jl
+++ b/src/reliability.jl
@@ -51,7 +51,11 @@ item 4: 0.7826
 ```
 """
 function cronbachalpha(covmatrix::AbstractMatrix{<:Real})
-    isposdef(covmatrix) || throw(ArgumentError("Covariance matrix must be positive definite."))
+    if !isposdef(covmatrix)
+        throw(ArgumentError("Covariance matrix must be positive definite. " *
+                            "Maybe you passed the data matrix instead of its covariance matrix? " *
+                            "If so, call `cronbachalpha(cov(...))` instead."))
+    end
     k = size(covmatrix, 2)
     k > 1  || throw(ArgumentError("Covariance matrix must have more than one column."))
     v = vec(sum(covmatrix, dims=1))