stub: Add sequence vectors.

* vector/stub.xml: Add sequence vectors.

core/vector/stub.xml

@@ -40,6 +40,16 @@
       <t:n-vector n="@current_n@" name="NVEC{@current_n@}"
                   value="0" />
     </t:for-each-n>
+
+
+    <section title="Sequence Vectors">
+      Sequence n-vectors are of length~$n$ and have a sequence of values
+        from~$0$ to~$n-1$.
+
+      <t:for-each-n start="1" end="10" step="1">
+        <t:n-vector n="@current_n@" name="NVEC{@current_n@}_SEQ" />
+      </t:for-each-n>
+    </section>
   </section>
 
 
@@ -66,14 +76,18 @@
       <param name="@n@"     desc="Number of vector elements" />
       <param name="@name@"  desc="Resulting vector constant name" />
 
-      <param name="@value@" desc="Value of elements (default n-1)">
-        <text>0</text>
-      </param>
+      <param name="@value@"
+             desc="Value of elements (optional; default n-1)" />
 
 
       <const name="@name@" desc="{@n@}-vector" set="vector">
         <t:for-each-n start="1" end="@n@" step="1">
-          <item value="@value@" desc="Vector value" />
+          <if name="@value@">
+            <item value="@value@" desc="Vector value" />
+          </if>
+          <unless name="@value@">
+            <item value="@current_n_dec@" desc="Vector value" />
+          </unless>
         </t:for-each-n>
       </const>
     </template>