Clarify documentation on periodic table extrapolation

Modelica/Blocks/Tables.mo

@@ -156,7 +156,13 @@ extrapolation = 1: Hold the first or last value of the table,
                    (If smoothness is LinearSegments or ConstantSegments
                    this means to extrapolate linearly through the first/last
                    two table points.).
-              = 3: Periodically repeat the table data (periodical function).
+              = 3: Periodically repeat the table data (periodical function), 
+                   where the repetition period is table[end,1]-table[1,1].
+                   For u = table[end,1] the result is table[end,2]. However for the
+                   limit of u downwards to table[end,1] the result is table[<strong>1</strong>,2].
+                   This implies that for correct reproduction of a periodic function
+                   the first and last data values should be the same 
+                   (table[1,2] = table[end,2]).
               = 4: No extrapolation, i.e. extrapolation triggers an error
 </pre></blockquote></li>
 <li>If the table has only <strong>one row</strong>, the table value is returned,
@@ -427,7 +433,13 @@ extrapolation = 1: Hold the first or last value of the table,
                    (If smoothness is LinearSegments or ConstantSegments
                    this means to extrapolate linearly through the first/last
                    two table points.).
-              = 3: Periodically repeat the table data (periodical function).
+              = 3: Periodically repeat the table data (periodical function), 
+                   where the repetition period is table[end,1]-table[1,1].
+                   For u = table[end,1] the result is table[end,2]. However for the
+                   limit of u downwards to table[end,1] the result is table[<strong>1</strong>,2].
+                   This implies that for correct reproduction of a periodic function
+                   the first and last data values should be the same 
+                   (table[1,2] = table[end,2]).
               = 4: No extrapolation, i.e. extrapolation triggers an error
 </pre></blockquote></li>
 <li>If the table has only <strong>one row</strong>, the table value is returned,
@@ -634,7 +646,15 @@ extrapolation = 1: Hold the first or last values of the table,
                    (If smoothness is LinearSegments or ConstantSegments
                    this means to extrapolate linearly through the first/last
                    two table points.).
-              = 3: Periodically repeat the table data (periodical function).
+              = 3: Periodically repeat the table data (periodical function), 
+                   where the repetition period is table[end,1]-table[2,1] and 
+                   table[1,end]-table[1,2] for columns and rows respectively.
+                   Assuming u1 is one of the abscissa values: for u2 = table[1,end]
+                   the result is table[u1,end]. However for the lim of u2 downwards 
+                   to table[1,end] the result is table[u1,<strong>2</strong>].
+                   This implies that for correct reproduction of a periodic function 
+                   the first and last rows/columns should be the same
+                   (table[2,2:] = table[end,2:] and table[2:,2] = table[2:,end]).
               = 4: No extrapolation, i.e. extrapolation triggers an error
 </pre></blockquote></li>
 <li>If the table has only <strong>one element</strong>, the table value is returned,
@@ -832,7 +852,15 @@ extrapolation = 1: Hold the first or last values of the table,
                    (If smoothness is LinearSegments or ConstantSegments
                    this means to extrapolate linearly through the first/last
                    two table points.).
-              = 3: Periodically repeat the table data (periodical function).
+              = 3: Periodically repeat the table data (periodical function), 
+                   where the repetition period is table[end,1]-table[2,1] and 
+                   table[1,end]-table[1,2] for columns and rows respectively.
+                   Assuming u1 is one of the abscissa values: for u2 = table[1,end]
+                   the result is table[u1,end]. However for the lim of u2 downwards 
+                   to table[1,end] the result is table[u1,<strong>2</strong>].
+                   This implies that for correct reproduction of a periodic function 
+                   the first and last rows/columns should be the same
+                   (table[2,2:] = table[end,2:] and table[2:,2] = table[2:,end]).
               = 4: No extrapolation, i.e. extrapolation triggers an error
 </pre></blockquote></li>
 <li>If the table has only <strong>one element</strong>, the table value is returned,