[mapReduce] improve the documentation on "reduce" operator

OPERATORS

@@ -99,8 +99,7 @@ Operator catalog:
    Cond2         ifthenelse      If then else
    Condc         ifthenc         If then constant
    Condc         ifnotthenc      If not then constant
-   MapReduce     reduce          Reduce input file variables for locations, where mask is non-zero.
-   MapReduce     unreduce        Unpack input fields to given grid description
+   MapReduce     reduce          Reduce input file variables to locations, where mask is non-zero.
 -------------------------------------------------------------
    Comparison
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doc/tex/mod/MapReduce

 @BeginModule
 @NewPage
 @Name      = MapReduce
-@Title     = Reduce grid to user-definde mask - unpack to target grid
+@Title     = Reduce fields to user-defined mask
 @Section   = Conditional selection
 @Class     = Conditional
 @Arguments = ifile ofile
-@Operators = reduce unreduce
+@Operators = reduce
 
 @BeginDescription
-This module contains operators for data reduction based on a user defined mask.
+This module holds an operator for data reduction based on a user defined mask.
+The output grid is unstructured and includes coordinate bounds.
 @EndDescription
 @EndModule
 
 
 @BeginOperator_reduce
 @Name      = reduce
-@Title     = Reduce input file variables for locations, where mask is non-zero.
+@Title     = Reduce input file variables to locations, where mask is non-zero.
              Horizontal grids of @file{mask} and @file{ifile} must be identical
 @Parameter = mask
 
-@BeginDescription
-Performs a transformation to an unstructured grid including coordinate bounds
-@EndDescription
 @EndOperator
 @BeginParameter
 @Item = mask
-STRING  Target mask
+STRING  file which holds the mask field
 @EndParameter
 
 @BeginExample

src/operator_help.h

@@ -740,23 +740,17 @@ static const char *CondcHelp[] = {
 
 static const char *MapReduceHelp[] = {
     "NAME",
-    "    reduce, unreduce - Reduce grid to user-definde mask - unpack to target grid",
+    "    reduce - Reduce fields to user-defined mask",
     "",
     "SYNOPSIS",
     "    reduce,mask  ifile ofile",
-    "    unreduce,grid  ifile ofile",
     "",
     "DESCRIPTION",
-    "    This module contains operators for data reduction based on a user defined mask.",
-    "",
-    "OPERATORS",
-    "    reduce    Reduce input file variables for locations, where mask is non-zero.",
-    "              Performs a transformation to an unstructured grid including coordinate bounds",
-    "    unreduce  Unpack input fields to given grid description",
-    "              Blowup the input fields towards given grid without changing the values",
+    "    This module holds an operator for data reduction based on a user defined mask.",
+    "    The output grid is unstructured and includes coordinate bounds.",
     "",
     "PARAMETER",
-    "    mask  STRING  Target mask",
+    "    mask  STRING  file which holds the mask field",
     NULL
 };