now an ordinaly vector A can multiply in three ways:
1.Multiply a scalar a :Aa;
2.Multiply another vector B, via the dot product:A.B;
3.Multiply another vector via the cross product:A*B.
Correspondingly ,there are three ways the operator B can act:
1.On a scalar function T: BT (the gradient):
2.On a vector function V,via the dot product:B.v(the divergence);
3.on a vector function v. via the cross product: B*v(the curl).
Wc have already discussed the gradient. In the following section we examine the other two vector derivatives : divergence and curl.