Expose python expm1 function

Signed-off-by: Jason T. Brown <[email protected]>

Author: vpipkt

docs/src/main/tut/reference.md

@@ -547,7 +547,7 @@ _Python_:
 
 _SQL_: `rf_log1p`
 
-Performs natural logarithm of cell values plus one. Invers of @ref:[`expm1`](reference.md#expm1).
+Performs natural logarithm of cell values plus one. Inverse of @ref:[`expm1`](reference.md#expm1).
 
 ### Tile Statistics
 

pyrasterframes/python/pyrasterframes/rasterfunctions.py

@@ -243,7 +243,7 @@ def _(data_tile, mask_tile, mask_value):
     'exp': 'Performs cell-wise exponential',
     'exp2': 'Compute 2 to the power of cell values',
     'exp10': 'Compute 10 to the power of cell values',
-    'exp1m': 'Performs cell-wise exponential, then subtract one',
+    'expm1': 'Performs cell-wise exponential, then subtract one',
     'resample': 'Resample tile to different size based on scalar factor or tile whose dimension to match',
 
     # ------- JTS functions -------

pyrasterframes/python/tests/PyRasterFramesTests.py

@@ -101,6 +101,7 @@ def test_general(self):
             .withColumn('ascii', render_ascii(self.tileCol)) \
             .withColumn('log', log(self.tileCol)) \
             .withColumn('exp', exp(self.tileCol)) \
+            .withColumn('expm1', expm1(self.tileCol)) \
             .withColumn('round', round(self.tileCol))
 
         df.show()