commit fb3fc691ab77748e13b4caf9b5b97f1761721670
Author: Dan Howe <d.howe@wrl.unsw.edu.au>
Date:   Thu Sep 6 17:14:38 2018 +1000

    Initial commit

diff --git a/scaling/froude.py b/scaling/froude.py
new file mode 100644
index 0000000..126a095
--- /dev/null
+++ b/scaling/froude.py
@@ -0,0 +1,73 @@
+import pint
+
+
+def _convert(x, length_scale_factor, from_unit, to_unit):
+
+    # Initialise unit definitions
+    ureg = pint.UnitRegistry()
+
+    # Calculate unit conversion factor
+    from_unit = ureg[from_unit]
+    to_unit = ureg[to_unit]
+    unit_conversion_factor = (1 * from_unit).to(to_unit).magnitude
+
+    # Define Froude scaling relationships
+    froude_l_exponent = 1
+    froude_t_exponent = 1 / 2
+    froude_m_exponent = 3
+
+    # Calculate Froude scaling factor
+    froude_scale_factor = length_scale_factor**(
+        from_unit.dimensionality['[length]'] * froude_l_exponent +
+        from_unit.dimensionality['[time]'] * froude_t_exponent +
+        from_unit.dimensionality['[mass]'] * froude_m_exponent)
+
+    # Scale time (dataframe only)
+    try:
+        x.index *= length_scale_factor**froude_t_exponent
+    except AttributeError:
+        pass
+
+    # Scale values
+    x *= froude_scale_factor
+
+    # Convert to output units
+    x *= unit_conversion_factor
+
+    return x
+
+
+def proto_to_model(x_proto, length_scale, from_unit, to_unit):
+    """Convert prototype value(s) to model value(s) in specified units.
+
+    Args:
+        x_proto:          prototype values (array_like, or pandas dataframe)
+        length_scale:     ratio between prototype and model dimensions (float)
+        from_unit (str):  unit of input value(s)
+        to_unit (str):    unit of output value(s)
+
+    Returns:
+        input values in model scale
+    """
+
+    length_scale_factor = 1 / length_scale
+
+    return _convert(x_model, length_scale_factor, from_unit, to_unit)
+
+
+def model_to_proto(x_model, length_scale, from_unit, to_unit):
+    """Convert model value(s) to prototype value(s) in specified units.
+
+    Args:
+        x_model:          model values (array_like, or pandas dataframe)
+        length_scale:     ratio between prototype and model dimensions (float)
+        from_unit (str):  unit of input value(s)
+        to_unit (str):    unit of output value(s)
+
+    Returns:
+        input values in prototype scale
+    """
+
+    length_scale_factor = length_scale
+
+    return _convert(x, length_scale_factor, from_unit, to_unit)