From 9874241bd85ab55742bad1740723796b97fc6883 Mon Sep 17 00:00:00 2001
From: Dan Howe <d.howe@wrl.unsw.edu.au>
Date: Mon, 10 Sep 2018 19:15:13 +1000
Subject: [PATCH] Add scaling_exponent() function

---
 scaling/froude.py    | 17 +++++++++++++++++
 tests/froude_test.py |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/scaling/froude.py b/scaling/froude.py
index ba017b2..2091ae6 100644
--- a/scaling/froude.py
+++ b/scaling/froude.py
@@ -95,3 +95,20 @@ def dimensions(unit):
             s += '{}^{:g} '.format(symbol, exponent)
 
     return s.strip()
+
+
+def scaling_exponent(unit):
+    """Convert prototype value(s) to model value(s) in specified units.
+
+    Args:
+        unit (str):  unit of quantity to be scaled
+
+    Returns:
+        scaling factor
+    """
+    # Calculate Froude scaling factor
+    scaling_exponent = (UREG(unit).dimensionality['[length]'] * LENGTH_EXPONENT
+                        + UREG(unit).dimensionality['[time]'] * TIME_EXPONENT +
+                        UREG(unit).dimensionality['[mass]'] * MASS_EXPONENT)
+
+    return scaling_exponent
diff --git a/tests/froude_test.py b/tests/froude_test.py
index de2b008..d5c713d 100644
--- a/tests/froude_test.py
+++ b/tests/froude_test.py
@@ -15,3 +15,8 @@ def test_unit_dimensions():
     assert froude.dimensions('kg') == 'M^1'
     assert froude.dimensions('s') == 'T^1'
     assert froude.dimensions('N') == 'L^1 M^1 T^-2'
+
+def test_scaling_exponent():
+    assert froude.scaling_exponent('m') == 1
+    assert froude.scaling_exponent('kg') == 3
+    assert froude.scaling_exponent('s') == 0.5