support multiplication of DVTI by a constant

src/fields.jl

@@ -188,6 +188,11 @@ function Base.(:+)(f1::DVTI, f2::DVTI)
     return DVTI(f1.data + f2.data)
 end
 
+""" Multiply DCTI field with a constant ``c``. """
+function Base.(:*){T<:Real}(c::T, field::DVTI)
+    return DVTI(c*field.data)
+end
+
 function Base.vec(field::DVTI)
     return [field.data...;]
 end