optimize: add doc comments for Location fields

optimize/minimize.go

@@ -35,9 +35,22 @@ type Task struct {
 
 // Location represents a location in the optimization procedure.
 type Location struct {
+	// X is the function input for the location.
 	X []float64
+	// F is the result of evaluating the function at X.
 	F float64
+	// Gradient holds the first-order partial derivatives
+	// of the function at X.
+	// The length of Gradient must match the length of X
+	// or be zero. If the capacity of Gradient is less
+	// than the length of X, a new slice will be allocated.
 	Gradient []float64
+	// Hessian holds the second-order partial derivatives
+	// of the function at X.
+	// The dimensions of Hessian must match the length of X
+	// or Hessian must be nil or empty. If Hessian is nil
+	// a new mat.SymDense will be allocated, if it is empty
+	// it will be resized to match the length of X.
 	Hessian *mat.SymDense
 }