Merge branch 'find'

src/Find.jl

@@ -37,7 +37,14 @@ Find a volume which leads to the given pressure, energy, or bulk modulus based o
     an array or a tuple, of which only the maximum and minimum values will be used in the
     root-finding process.
 """
-findvolume(f, y, x0, method) = find_zero(v -> f(v) - y, x0, method)
+function findvolume(f, y, x0, method)
+    v0 = find_zero(v -> f(v) - y, x0, method)
+    if v0 < zero(v0)
+        error("the volume found is negative!")
+    else
+        return v0
+    end
+end # function findvolume
 function findvolume(f, y, x0)
     for T in [subtypes(AbstractBisection); subtypes(AbstractAlefeldPotraShi)]
         @info("Using method \"$T\"...")